Beyond Order: Random, Aperiodic, and Hyperuniform Photonic Materials: introduction to the special issue Negro, L. D. A. L., C. A. O. Hui, M. Filoche, S. A. Schulz, S. Vignolini, and D. S. Wiersma Optical Materials Express 14, no. 5, 12931294 (2024)
Résumé: The editors introduce the feature issue on “Beyond Order: Random, Aperiodic, and Hyperuniform Photonic Materials,” which includes nine articles.


Spatial coherence in strongly scattering media Pierrat, R., R. Elaloufi, J.J. Greffet, and R. Carminati Journal of the Optical Society of America A 22, no. 11, 2329 (2005)


Photon diffusion coefficient in scattering and absorbing media Pierrat, R., J.J. Greffet, and R. Carminati Journal of the Optical Society of America A 23, no. 5, 1106 (2006)


Light propagation in multilayered scattering media beyond the diffusive regime Elaloufi, R., S. Arridge, R. Pierrat, and R. Carminati Applied Optics 46, no. 13, 2528 (2007)


Threshold of random lasers in the incoherent transport regime Pierrat, R., and R. Carminati Physical Review A 76, no. 2 (2007)


The influence of the scattering anisotropy parameter on diffuse reflection of light Pierrat, R., N. B. Braham, L. F. RojasOchoa, R. Carminati, and F. Scheffold Optics Communications 281, no. 1, 1822 (2008)


Transport equation for the time correlation function of scattered field in dynamic turbid media Pierrat, R. Journal of the Optical Society of America A 25, no. 11, 2840 (2008)


Enhancement of radiation trapping for quasiresonant scatterers at low temperature Pierrat, R., B. Grémaud, and D. Delande Physical Review A 80, no. 1 (2009)


Asymmetrical wakes over anisotropic bathymetries Euvé, L.P., A. Maurel, P. Petitjeans, and V. Pagneux Journal of Fluid Mechanics 984 (2024)
Résumé: The study investigates the impact of a vertically layered bathymetry, consisting of submerged vertical plates, on a ship wake through theoretical analysis and experimental realization. For subwavelength distances between the plates, the analysis relies on a homogenized model that provides an effective, anisotropic, dispersion relation for the propagation of water waves. Our findings reveal that a highly asymmetric wake can be achieved, with the degree of asymmetry contingent upon the ship propagation direction in relation to the plate orientation. This anisotropy is characterized with respect to water depth and to ship length using the dimensionless depth and hull Froude numbers. Laboratory experiments align closely with theoretical predictions, confirming that the asymmetry of the wake can indeed be managed through manipulation of bathymetric conditions.


Multiple scattering theory in one dimensional space and time dependent disorder: average field [Invited] Selvestrel, A., J. Rocha, R. Carminati, and R. Pierrat Optical Materials Express 14, no. 3, 801815 (2024)
Résumé: We theoretically study the propagation of light in onedimensional space and timedependent disorder. The disorder is described by a fluctuating permittivity ε(x, t) exhibiting shortrange correlations in space and time, without cross correlation between them. Depending on the illumination conditions, we show that the intensity of the average field decays exponentially in space or in time, with characteristic length or time defining the scattering meanfree path ℓs and the scattering meanfree time τs. In the weak scattering regime, we provide explicit expressions for ℓs and τs, that are checked against rigorous numerical simulations.


Light in correlated disordered media Vynck, K., R. Pierrat, R. Carminati, L. S. FroufePérez, F. Scheffold, R. Sapienza, S. Vignolini, and J. J. Sáenz Reviews of Modern Physics 95, no. 4 (2023)


Characterization of ejecta in shock experiments with multiple light scattering Don Jayamanne, J. A., J. R. Burie, O. Durand, R. Pierrat, and R. Carminati Journal of Applied Physics 135, no. 7 (2024)
Résumé: Upon impact, the free surface of a solid metal may eject a cloud of fast and fine particles. Photon Doppler Velocimetry (PDV) is one of the optical diagnostics used to characterize these ejecta. Although the technique provides a direct way to estimate the particle velocities in the single scattering regime, it has been shown that multiple scattering cannot be neglected in real ejecta. Here, we derive a model for PDV measurements starting from the first principles of wave scattering. We establish rigorously the relationship between the specific intensity and the measured signal, as well as the Radiative Transport Equation (RTE) that describes the evolution of the specific intensity upon scattering and absorption in dynamic ejecta, including the effects of inelastic scattering and inhomogeneities in the optical properties. We also establish rigorously the connection between the Monte Carlo scheme used for numerical simulations and the solution to the RTE. Using numerical simulations, we demonstrate the crucial contribution of multiple scattering to PDV spectrograms as well as the effect of statistical inhomogeneities in particle size distribution. These results could substantially impact the analysis of ejecta by PDV.


Backscattering reduction in a sharply bent water wave channel Kucher, S., A. Koźluk, P. Petitjeans, A. Maurel, and V. Pagneux Physical Review B 108, no. 21 (2023)
Résumé: We study theoretically and experimentally how to reduce the backscattering of water waves in a channel with multiple turns. We show that it is possible not only to cancel backscattering but also to achieve a remarkable transmission in such geometries. In order to avoid the reflection that naturally arises at each turn of the waveguide, an anisotropic metamaterial made of closely spaced thin vertical plates is used. The efficiency of the metamaterial arrangement depends only slightly on the frequency of the incident wave, as long as its wavelength is much larger than the periodicity of the array. This phenomenon is applies not only to water wave channels but also to any type of waves with Neumann boundary conditions.


Realizationdependent model of hopping transport in disordered media Thayil, A., and M. Filoche Applied Physics Letters 123, no. 25 (2023)


Perfect Resonant Absorption of Guided Water Waves by AutlerTownes Splitting Euvé, L. P., K. Pham, R. Porter, P. Petitjeans, V. Pagneux, and A. Maurel Physical review letters 131, no. 20, 204002 (2023)
Résumé: The control of guided water wave propagation based on the AutlerTownes splitting resonance concept is demonstrated experimentally, numerically, and theoretically. Complete wave absorption is achieved using an asymmetric pointlike scatterer made of two closely spaced resonant side channels connected to a guide and designed so that its energy leakage is in perfect balance with the inherent viscous losses in the system. We demonstrate that the nature of the resonators and guide junction completely controls the positions of the wave numbers at the reflection and transmission zeros on the real axis; the asymmetry of the resonators completely controls their positions on the imaginary axis. Thus, by adjusting these two independent parameters, we obtain a zero reflection and transmission.


Photon diffusion in space and time in a secondordernonlinear disordered medium Samanta, R., R. Pierrat, R. Carminati, and S. Mujumdar Physical Review A 108, no. 5 (2023)
Résumé: We report experimental and theoretical investigations of photon diffusion in a secondordernonlinear disordered medium under conditions of strong nonlinearity. Experimentally, photons at the fundamental wavelength (λ=1064nm) are launched into the structure in the form of a cylindrical pellet, and the secondharmonic (λ=532nm) photons are temporally analyzed in transmission. For comparison, separate experiments are carried out with incident green light at λ=532nm. We observe that the secondharmonic light peaks earlier compared to the incident green photons. Next, the sideways spatial scattering of the fundamental as well as secondharmonic photons is recorded. The spatial diffusion profiles of secondharmonic photons are seen to peak deeper inside the medium in comparison to both the fundamental and incident green photons. In order to give more physical insights into the experimental results, a theoretical model is derived from first principles. It is based on the coupling of transport equations. Solved numerically using a Monte Carlo algorithm and experimentally estimated transport parameters at both wavelengths, it shows excellent semiquantitative agreement with the experiments for both fundamental and secondharmonic light.


Optimization of plasmonic metasurfaces: A homogenizationbased design Lebbe, N., K. Pham, and A. Maurel Journal of Computational Physics 495 (2023)
Résumé: This article deals with the optimization of resonant plasmonic metasurfaces through their surfacehomogenized counterpart. The derivation of effective transition conditions that takes into account the spatially varying geometries is done using locally periodic surface homogenization. The resulting model reduces the numerical cost of simulating these metasurfaces, thus allowing to find their design using adjointbased optimization methods. This new algorithm is presented in details, together with various numerical examples to asses its validity and compare its performance with the classical design based on local phase matching.


Carrier localization in IIInitride versus conventional IIIV semiconductors: A study on the effects of alloy disorder using landscape theory and the Schrödinger equation Tsai, T.Y., K. S. Qwah, J.P. Banon, M. Filoche, C. Weisbuch, Y.R. Wu, and J. S. Speck Physical Review Applied 20, 044069 (2023)


Subwavelength pulse focusing and perfect absorption in the Maxwell fisheye Lefebvre, G., M. Dubois, Y. Achaoui, R. K. Ing, M. Fink, S. Guenneau, and P. Sebbah Applied Physics Letters 123, no. 13 (2023)
Résumé: Maxwell's fisheye is a paradigm for an absolute optical instrument with a refractive index deduced from the stereographic projection of a sphere on a plane. We investigate experimentally the dynamics of flexural waves in a thin plate with a thickness varying according to the Maxwell fisheye index profile and a clamped boundary. We demonstrate subwavelength focusing and temporal pulse compression at the image point. This is achieved by introducing a sink emitting a cancelling signal optimally shaped using a timereversal procedure. Perfect absorption and outward going wave cancellation at the focus point are demonstrated. The time evolution of the kinetic energy stored inside the cavity reveals that the sink absorbs energy out of the plate ten times faster than the natural decay rate.


On the role of viscoelasticity in mucociliary clearance: a hydrodynamic continuum approach Choudhury, A., M. Filoche, N. M. Ribe, N. Grenier, and G. Dietze Journal of Fluid Mechanics 971, A33 (2023)
Résumé: We present numerical and analytical predictions of mucociliary clearance based on the continuum description of a viscoelastic mucus film, where momentum transfer from the beating cilia is represented via a Navierslip boundary condition introduced by Bottier et al. (PLoS Comput. Biol., vol. 13, issue 7, 2017a, e1005552). Mucus viscoelasticity is represented via the OldroydB model, where the relaxation time and the viscosity ratio have been fitted to experimental data for the storage and loss moduli of different types of real mucus, ranging from healthy to diseased conditions. We solve numerically the fully nonlinear governing equations for inertialess flow, and develop analytical solutions via asymptotic expansion in two limits: (i) weak viscoelasticity, i.e. low Deborah number; (ii) low cilia beat amplitude (CBA). All our approaches predict a drop in the mucus flow rate in relation to the Newtonian reference value, as the cilia beat frequency is increased. This relative drop increases with decreasing CBA and slip length. In diseased conditions, e.g. mucus properties characteristic of cystic fibrosis, the drop reaches 30%
in the physiological frequency range. In the case of healthy mucus, no significant drop is observed, even at very high frequency. This contrasts with the deterioration of microorganism propulsion predicted by the lowamplitude theory of Lauga (Phys. Fluids, vol. 19, issue 8, 2007, 083104), and is due to the larger beat amplitude and slip length associated with mucociliary clearance. In the physiological range of the cilia beat frequency, the lowamplitude prediction is accurate for both healthy and diseased conditions. Finally, we find that shearthinning, modelled via a multimode Giesekus model, does not significantly alter our weakly viscoelastic and lowamplitude predictions based on the OldroydB model.


Degree of polarization of light scattered from correlated surface and bulk disorders Banon, J. P., I. Simonsen, and R. Carminati Optics Express 31, no. 17, 2802628039 (2023)
Résumé: Using a single scattering theory, we derive the expression of the degree of polarization of the light scattered from a layer exhibiting both surface and volume scattering. The expression puts forward the intimate connection between the degree of polarization and the statistical correlation between surface and volume disorders. It also permits a quantitative analysis of depolarization for uncorrelated, partially correlated and perfectly correlated disorders. We show that measuring the degree of polarization could allow one to assess the surfacevolume correlation function, and that, reciprocally, the degree of polarization could be engineered by an appropriate design of the correlation function.


Revisiting effective acoustic propagation in labyrinthine metasurfaces Hagström, J. Z., K. Pham, and A. Maurel Wave Motion 122, 103196 (2023)
Résumé: We revisit the modelling of labyrinthine metasurfaces with space coiling design. To do so, we use homogenization theory which allows us to replace the actual structure by a slab filled with an effective, homogeneous and anisotropic, medium. The effective medium is highly anisotropic as the propagation is allowed in one direction only and its effective refractive index is obtained unambiguously thanks to the resolution of a static cellproblem. The result is compared to a classical, twostep, model which follows the intuitive idea that a coiled labyrinth and a slot being its uncoiled version behave the same. Beyond the approximation of such statement (the evanescent fields triggered at the turning regions of the labyrinth are neglected), we stress the difficulty in defining unambiguously the length of the uncoiled labyrinth.


How spacetime modulations modify spoof surface plasmons and scattering properties in acoustic metagratings Pham, K., and A. Maurel Physical Review B 108, no. 2 (2023)
Résumé: We analyze the propagation of acoustic waves in a spacetime (ST) modulated grating moving at constant velocity and surrounded by air. By means of asymptotic techniques, we derive in the subwavelength regime a homogenized nonreciprocal model in which the grating is replaced by an equivalent bianisotropic slab at the boundaries of which effective jump conditions apply, that encapsulate the effect of the evanescent fields. This effective framework allows to characterize analytically the properties of ST modulated metagratings in terms of scattering properties and guided wave dispersion. First we derive the closedform dispersion relation of spoof surface plasmon polaritons (SPPs) and show the appearance of multiple redshifted or blueshifted branches due to the ST modulation. Next, we provide in the radiative region closedform expressions for the Brewster angle and FabryPérot resonances and show how the ST modulation heavily modifies the complex spectra. Finally, we illustrate the potential of such a system to achieve negative refraction or perfect transparency by playing on the modulation. Throughout the study, our analysis is validated by comparison with direct numerical simulations.


Low and highenergy localization landscapes for tightbinding Hamiltonians in twodimensional lattices RazoLópez, L. A., G. J. Aubry, M. Filoche, and F. Mortessagne Physical Review Research 5, no. 2 (2023)
Résumé: Localization of electronic wave functions in modern twodimensional (2D) materials such as graphene can impact drastically their transport and magnetic properties. The recent localization landscape (LL) theory has brought many tools and theoretical results to understand such localization phenomena in the continuous setting, but with very few extensions so far to the discrete realm or to tightbinding Hamiltonians. In this paper, we show how this approach can be extended to almost all known 2D lattices and propose a systematic way of designing LL even for higher dimensions. We demonstrate in detail how this LL theory works and predicts accurately not only the locations, but also the energies of localized eigenfunctions in the low and highenergy regimes for the honeycomb and hexagonal lattices, making it a highly promising tool for investigating the role of disorder in these materials.


Negative refraction of water waves by hyperbolic metamaterials Euvé, L. P., K. Pham, and A. Maurel Journal of Fluid Mechanics 961 (2023)
Résumé: We study the propagation of water waves in a threedimensional device alternating open canals and resonant canals with subwavelength resonances. The dispersion of water waves in such a medium is obtained by analysing the full threedimensional problem and combining BlochFloquet analysis with an asymptotic technique. We obtain the closed forms of the dispersions for resonant canals containing one or two resonators, which depend on only two functions associated with symmetric and antisymmetric modes, and on a geometric parameter analogous to the hopping parameter in topological systems. The analysis of the complete band structure reveals frequency ranges alternating between elliptical and hyperbolic dispersions; in particular, the hyperbolic regime gives rise to a negative effective water depth with a consequent negative refraction. Throughout the course of our study, our theoretical results are validated by comparison with numerical calculations of the full threedimensional problem.


Second Order Homogenization of Subwavelength Stratified Media Including Finite Size Effect Marigo, J.J., and A. Maurel SIAM Journal on Applied Mathematics 77, no. 2, 721743 (2017)


Effective Dynamic Properties of a Row of Elastic Inclusions: The Case of Scalar Shear Waves Marigo, J.J., A. Maurel, K. Pham, and A. Sbitti Journal of Elasticity 128, no. 2, 265289 (2017)


Revisiting the anisotropy of metamaterials for water waves Maurel, A., J.J. Marigo, P. Cobelli, P. Petitjeans, and V. Pagneux Physical Review B 96, no. 13 (2017)


Light scattering by periodic rough surfaces: equivalent jump conditions Gallas, B., A. Maurel, J.J. Marigo, and A. Ourir Journal of the Optical Society of America A 34, no. 12, 2181 (2017)


Effective boundary condition for the reflection of shear waves at the periodic rough boundary of an elastic body Maurel, A., J.J. Marigo, and K. Pham Vietnam Journal of Mechanics 40, no. 4, 303323 (2018)


Scattering of acoustic waves by a nonlinear resonant bubbly screen Pham, K., J.F. Mercier, D. Fuster, J.J. Marigo, and A. Maurel Journal of Fluid Mechanics 906 (2020)


The interplay between Fano and Fabry–Pérot resonances in dualperiod metagratings Zhou Hagström, J., A. Maurel, and K. Pham Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2255 (2021)


Stable GSTC Formulation for Maxwell’s Equations Lebbe, N., K. Pham, and A. Maurel IEEE Transactions on Antennas and Propagation 70, no. 8, 68256840 (2022)


Modeling of fullfield optical coherence tomography in scattering media Tricoli, U., and R. Carminati Journal of the Optical Society of America A 36, no. 11, C122 (2019)


Mathematical Analysis of Plasmonic Nanoparticles: The Scalar Case Ammari, H., P. Millien, M. Ruiz, and H. Zhang Archive for Rational Mechanics and Analysis 224, no. 2, 597658 (2017)


Shape and size dependence of dipolar plasmonic resonance of nanoparticles Ammari, H., and P. Millien Journal de Mathématiques Pures et Appliquées 129, 242265 (2019)


Subwavelength resonant dielectric nanoparticles with high refractive indices Ammari, H., A. Dabrowski, B. Fitzpatrick, P. Millien, and M. Sini Mathematical Methods in the Applied Sciences 42, no. 18, 65676579 (2019)


Mathematical modelling of plasmonic strain sensors Ammari, H., P. Millien, and A. L. Vanel Journal of Inverse and Illposed Problems 30, no. 1, 117126 (2020)


Perturbation of the scattering resonances of an open cavity by small particles. Part I: the transverse magnetic polarization case Ammari, H., A. Dabrowski, B. Fitzpatrick, and P. Millien Zeitschrift für angewandte Mathematik und Physik 71, no. 4 (2020)


Stability for Finite Element Discretization of Some Inverse Parameter Problems from Internal Data: Application to Elastography Bretin, E., P. Millien, and L. Seppecher SIAM Journal on Imaging Sciences 16, no. 1, 340367 (2023)


Perturbations of the scattering resonances of an open cavity by small particles: Part II—the transverse electric polarization case Ammari, H., A. Dabrowski, B. Fitzpatrick, and P. Millien Zeitschrift für angewandte Mathematik und Physik 72, no. 2 (2021)


Modal approximation for plasmonic resonators in the time domain: the scalar case Baldassari, L., P. Millien, and A. L. Vanel Partial Differential Equations and Applications 2, no. 4 (2021)


Localization landscape for interacting Bose gases in onedimensional speckle potentials Stellin, F., M. Filoche, and F. Dias Physical Review A 107, no. 4 (2023)
Résumé: While the properties and the shape of the ground state of a gas of ultracold bosons are well understood in harmonic potentials, they remain for a large part unknown in the case of random potentials. Here we use localizationlandscape (LL) theory to study the properties of the solutions to the GrossPitaevskii equation (GPE) in onedimensional (1D) speckle potentials. In the cases of attractive interactions, we find that the LL allows one to predict the position of the localization center of the ground state (GS) of the GPE. For weakly repulsive interactions, we point out that the GS of the quasi1D GPE can be understood as a superposition of a finite number
of singleparticle states, which can be computed by exploiting the LL. For intermediate repulsive interactions, we introduce a ThomasFermilike approach for the GS which holds in the smoothing regime, well beyond the usual approximation involving the original potential. Moreover, we show that, in the Lifshitz glass regime, the particle
density and the chemical potential can be well estimated by the LL. Our approach can be applied to any positivevalued random potential endowed with finiterange correlations and can be generalized to higherdimensional systems.


Homogenized transition conditions for plasmonic metasurfaces Lebbe, N., A. Maurel, and K. Pham Physical Review B 107, no. 8 (2023)
Résumé: The present study aims to model the optical response of plasmonic metasurfaces made of a periodic arrangement of metallic particles with arbitrary shape and subwavelength dimensions. By combining homogenization with quasistatic plasmonic eigenmode expansion, the metasurface is replaced by a zerothickness interface associated with frequencydependent effective susceptibilities. The resulting discontinuities of the fields are responsible for strong interaction with the incoming light at the resonances when the complex permittivity of the metal passes close to the real permittivity of an eigenmode. Our modeling provides a physical picture of resonances in plasmonic metasurfaces, and it allows for a huge decrease in the numerical cost of their computations. In addition, comparisons with direct numerics in two dimensions evidence its predictive force at any incidence, particle shape, and arrangement.


Superlocalisation of a pointlike emitter in a resonant environment: Correction of the mirage effect Baldassari, L., P. Millien, and A. L. Vanel Inverse Problems and Imaging 17, no. 2, 490506 (2023)
Résumé: In this paper, we show that it is possible to overcome one of the fundamental limitations of superresolution microscopy: the necessity to be in an optically homogeneous environment. Using recent modal approximation results from [10, 7], we show, as a proof of concept, that it is possible to recover the position of a single pointlike emitter in a known resonant environment from farfield measurements, with a precision two orders of magnitude below the classical Rayleigh limit. The procedure does not involve solving any partial differential equation, is computationally light (optimisation in Rd with d of the order of 10) and is therefore suited for the recovery of a very large number of single emitters.


Coherent backscattering of entangled photon pairs Safadi, M., O. Lib, H. C. Lin, C. W. Hsu, A. Goetschy, and Y. Bromberg Nature Physics (2023)
Résumé: Correlations between entangled photons are a key ingredient for testing fundamental aspects of quantum mechanics and an invaluable resource for quantum technologies. However, scattering from a dynamic medium typically scrambles and averages out such correlations. Here we show that multiply scattered entangled photons reflected from a dynamic complex medium remain partially correlated. In experiments and fullwave simulations we observe enhanced correlations, within an angular range determined by the transport mean free path, which prevail over disorder averaging. Theoretical analysis reveals that this enhancement arises from the interference between scattering trajectories, in which the photons leave the sample and are then virtually reinjected back into it. These paths are the quantum counterpart of the paths that lead to the coherent backscattering of classical light. This work points to opportunities for entanglement transport despite dynamic multiple scattering in complex systems.


The Electronic Disorder Landscape of Mixed Halide Perovskites Liu, Y., J. P. Banon, K. Frohna, Y. H. Chiang, G. TumenUlzii, S. D. Stranks, M. Filoche, and R. H. Friend ACS Energy Letters 8, no. 1, 250258 (2023)
Résumé: Band gap tunability of lead mixed halide perovskites makes them promising candidates for various applications in optoelectronics. Here we use the localization landscape theory to reveal that the static disorder due to iodide:bromide compositional alloying contributes at most 3 meV to the Urbach energy. Our modeling reveals that the reason for this small contribution is due to the small effective masses in perovskites, resulting in a natural length scale of around 20 nm for the “effective confining potential” for electrons and holes, with shortrange potential fluctuations smoothed out. The increase in Urbach energy across the compositional range agrees well with our optical absorption measurements. We model systems of sizes up to 80 nm in three dimensions, allowing us to accurately reproduce the experimentally observed absorption spectra of perovskites with halide segregation. Our results suggest that we should look beyond static contribution and focus on the dynamic temperature dependent contribution to the Urbach energy.


Reconstructing the Spatial Distribution of the Relative Shear Modulus in Quasistatic Ultrasound Elastography: Plane Stress Analysis Seppecher, L., E. Bretin, P. Millien, L. Petrusca, and E. Brusseau Ultrasound in Medicine and Biology (2023)
Résumé: Quasistatic ultrasound elastography (QSUE) is an imaging technique that mainly provides axial strain maps of tissues when the latter are subjected to compression. In this article, a method for reconstructing the relative shear modulus distribution within a linear elastic and isotropic medium, in QSUE, is introduced. More specifically, the plane stress inverse problem is considered. The proposed method is based on the variational formulation of the equilibrium equations and on the choice of adapted discretization spaces, and only requires displacement fields in the analyzed media to be determined. Results from plane stress and 3D numerical simulations, as well as from phantom experiments, showed that the method is able to reconstruct the different regions within a medium, with shear modulus contrasts that unambiguously reveal whether inclusions are stiffer or softer than the surrounding material. More specifically, for the plane stress simulations, inclusiontobackground modulus ratios were found to be very accurately estimated, with an error lower than 3%. For the 3D simulations, for which the plane stress conditions are no longer satisfied, these ratios were, as expected, less accurate, with an error that remained lower than 10% for two of the three cases analyzed but was around 34% for the last case. Concerning the phantom experiments, a comparison with a shear wave elastography technique from a clinical ultrasound scanner was also made. Overall, the inclusiontobackground shear modulus ratios obtained with our approach were found to be closer to those given by the phantom manufacturer than the ratios provided by the clinical system.


Speckle Decorrelation in Fundamental and SecondHarmonic Light Scattered from Nonlinear Disorder Samanta, R., R. Pierrat, R. Carminati, and S. Mujumdar Physical Review Applied 18, no. 5 (2022)
Résumé: Speckle patterns generated in a disordered medium carry a lot of information despite the apparent complete randomness in the intensity pattern. When the medium possesses ?(2) nonlinearity, the speckle is sensitive to the phase of the incident fundamental light, as well as the light generated within. Here, we examine the speckle decorrelation in the fundamental and secondharmonic transmitted light as a function of the varying power in the fundamental beam. At low incident powers, the speckle patterns produced by successive pulses exhibit strong correlations, which decrease with increasing power. The average correlation in the secondharmonic speckle decays faster than in the fundamental speckle. Next, we construct a theoretical model, backed up by numerical computations, to obtain deeper physical insights into the faster decorrelations in the secondharmonic light. While providing excellent qualitative agreement with the experiments, the model sheds light on the contribution of two effects in the correlations, namely, the generation of secondharmonic light and the propagation thereof.


Negative refraction in a singlephase flexural metamaterial with hyperbolic dispersion Marigo, J. J., A. Maurel, and K. Pham Journal of the Mechanics and Physics of Solids 170 (2023)
Résumé: We analyze the band structure of a singlephase metamaterial involving lowfrequency flexural resonances by combining asymptotic homogenization and Bloch–Floquet analysis. We provide the closedform expression of the dispersion relation in the whole Brillouin zone. The dispersion relation involves two effective, frequencydependent, mass densities associated with symmetric and antisymmetric flexural resonances of the beams at the microscopic scale. We demonstrate that our simple locallyresonant structure produces at lowfrequency bandgaps and, in the hyperbolic regions of the dispersion diagram, negative refraction. Our findings are validated by direct numerical calculations.


Diffraction grating with varying slit width: Quasiperiodic homogenization and its numerical implementation Pham, K., N. Lebbe, and A. Maurel Journal of Computational Physics 473, 111727 (2023)
Résumé: We study the diffraction of acoustic waves by thin grating with varying slit width. Using quasiperiodic homogenization, we derive an effective model in which the grating is replaced by effective jump conditions with effective parameters varying along the equivalent interface. The numerical implementations of the actual problem and of its homogenized counterpart are achieved using multimodal methods for a periodic grating with a macroperiod containing many slits with varying widths. The ability of the effective grating to reproduce the scattering properties of the actual one is inspected and discussed.


Pseudogap and Anderson localization of light in correlated disordered media Monsarrat, R., R. Pierrat, A. Tourin, and A. Goetschy Physical Review Research 4, no. 3 (2022)
Résumé: Among the remarkable scattering properties of correlated disordered materials, the origin of pseudogaps and the formation of localized states are some of the most puzzling features. Fundamental differences between scalar and vector waves in both these aspects make their comprehension even more problematic. Here we present an indepth and comprehensive analysis of the ordertodisorder transition in 2D resonant systems. We show with exact ab initio numerical simulations in finitesize hyperuniform media that localization of 2D vector waves can occur in the presence of correlated disorder, in a regime of moderate density of scatterers. On the contrary, no signature of localization is found for white noise disorder. This is in striking contrast with scalar waves, which localize at high density whatever the amount of correlation. For correlated materials, localization is associated with the formation of pseudogap in the density of states. We develop two complementary models to explain these observations. The first one uses an effective photonic crystaltype framework and the second relies on a diagrammatic treatment of the multiple scattering sequences. We provide explicit theoretical evaluations of the density of states and localization length in good agreement with numerical simulations. In this way, we identify the microscopic processes at the origin of pseudogap formation and clarify the role of the density of states for wave localization in resonant correlated media. The generality of our framework makes possible to apply our predictions for a large variety of scattering systems including dielectric structures with high quality factor, cold atoms, artificial atoms, as well as microwave resonators.


Coherent enhancement of optical remission in diffusive media Bender, N., A. Goetschy, C. W. Hsu, H. Yilmaz, P. J. Palacios, A. Yamilov, and H. Cao Proceedings of the National Academy of Sciences of the United States of America 119, no. 41 (2022)
Résumé: Remitted waves are used for sensing and imaging in diverse diffusive media from the Earth's crust to the human brain. Separating the source and detector increases the penetration depth of light, but the signal strength decreases rapidly, leading to a poor signaltonoise ratio. Here, we show, experimentally and numerically, that wavefront shaping a laser beam incident on a diffusive sample enables an enhancement of remission by an order of magnitude at depths of up to 10 transport mean free paths. We develop a theoretical model which predicts the maximal remission enhancement. Our analysis reveals a significant improvement in the sensitivity of remitted waves to local changes of absorption deep inside diffusive media. This work illustrates the potential of coherent wavefront control for noninvasive diffuse wave imaging applications, such as diffuse optical tomography and functional nearinfrared spectroscopy.


Diffraction grating with spacetime modulation Pham, K., and A. Maurel Journal of Computational Physics 469, 111528 (2022)
Résumé: We present a theoretical and numerical analysis of the diffraction of acoustic waves by spacetime modulated gratings with rigidtype modulations. This is done by deriving the form of the modes which are exact, uncoupled, solutions of the problem in the unbounded regions, inside and outside the grating. The dispersion of the modes is studied as a function of the ratio of the modulation speed to the speed of sound which shows that each spatial diffraction order is associated with a single temporal diffraction order. For a grating of finite extend, the solution is obtained as a superposition of these modes, which couple at the grating interfaces. This provides a numerical, multimodal, method when considering a truncated version of the solution. We provide analysis of the solutions in the harmonic and in the transient regimes.


Coalescence of Andersonlocalized modes at an exceptional point in 2D random media Bachelard, N., A. Schumer, B. Kumar, C. Garay, J. Arlandis, R. Touzani, and P. Sebbah Optics Express 30, no. 11, 1809818107 (2022)
Résumé: In nonHermitian settings, the particular position at which two eigenstates coalesce in the complex plane under a variation of a physical parameter is called an exceptional point. An open disordered system is a special class of nonHermitian system, where the degree of scattering directly controls the confinement of the modes. Herein a nonperturbative theory is proposed which describes the evolution of modes when the permittivity distribution of a 2D open dielectric system is modified, thereby facilitating to steer individual eigenstates to such a nonHermitian degeneracy. The method is used to predict the position of such an exceptional point between two Andersonlocalized states in a disordered scattering medium. We observe that the accuracy of the prediction depends on the number of localized states accounted for. Such an exceptional point is experimentally accessible in practically relevant disordered photonic systems.


Nonlinear Waves Passing over Rectangular Obstacles: Multimodal Method and Experimental Validation Monsalve, E., A. Maurel, V. Pagneux, and P. Petitjeans Fluids 7, no. 5, 145 (2022)
Résumé: We report a theoretical and experimental investigation of the propagation of nonlinear waves passing over a submerged rectangular step. A multimodal method allows calculating the firstand secondorder reflected and transmitted waves. In particular, at the second order, the propagation of free and bound waves is theoretically presented. A detailed analysis of the convergence of the secondorder problem shows that a finite truncation of the series of evanescent bound waves is necessary to obtain a smooth and convergent solution. The computed coefficients of the first and second harmonics are experimentally validated via a complete spacetimeresolved measurements of the wave propagation, which permits us to verify the relative amplitude, phase and spatial interference (beating) of the free and bound waves at the second order. This result can be useful in future multimodal models since it not only keeps the accuracy of the model with the inclusion of the first part of the evanescent bound terms (being also the dominants) but also ensures the convergence of the multimodal computation with an error that decreases as a function of the number of modes.


Purcell effect with extended sources: the role of the cross density of states Carminati, R., and M. Gurioli Optics Express 30, no. 10, 1617416183 (2022)
Résumé: We analyze the change in the spontaneous decay rate, or Purcell effect, of an extended quantum emitter in a structured photonic environment. Based on a simple theory, we show that the cross density of states is the central quantity driving interferences in the emission process. Using numerical simulations in realistic photonic cavity geometries, we demonstrate that a structured cross density of states can induce subradiance or superradiance, and change substantially the emission spectrum. Interestingly, the spectral lineshape of the Purcell effect of an extended source cannot be predicted from the sole knowledge of the spectral dependence of the local density of states.


Modeling AutlerTownes splitting and acoustically induced transparency in a waveguide loaded with resonant channels Porter, R., K. Pham, and A. Maurel Physical Review B 105, no. 13 (2022)
Résumé: We study acoustic wave propagation in a waveguide loaded with two resonant sidebranch channels. In the lowfrequency regime, onedimensional models are derived in which the effect of the channels are reduced to jump conditions across the junction. When the separation distance is on the scale of the wavelength, which is the case that is usually considered, the jump conditions involve a single channel and acoustically induced transparency occurs due to outofphase interferences between the two junctions. In contrast, when the separation distance is subwavelength, a single junction has to be considered and the jump conditions account for the evanescent field coupling the two channels. Such channel pairs can scatter as a dipole, resulting in perfect transmission due to AutlerTownes splitting. We show that combining the two mechanisms offers additional degrees of freedom to control the transmission spectra.


Spacetimeresolved measurements of the effect of pinned contact line on the dispersion relation of water waves Monsalve, E., A. Maurel, V. Pagneux, and P. Petitjeans Physical Review Fluids 7, no. 1 (2022)
Résumé: We report on an experimental investigation of the propagation of gravitycapillary waves in a narrow channel with a pinned contact line. By using Fourier transform profilometry we measure the static curved meniscus as well as the surface perturbation. By varying the channel width, between 7 and 15 times the capillary length, we show how edge constraints modify the surface curvature and therefore the dispersion relation. From the spacetimeresolved field, we obtain a decomposition of the linear mode onto transverse modes satisfying the condition of pinned contact line. This approach, in which we complement the theoretical model with experimental analysis, allows computations of wave numbers and natural frequencies with a robust statistics. We verify experimentally the convergence of the model and the pertinence of the linear approximation. In addition, we analyze the relative contribution of the experimentally measured static meniscus. An excellent agreement between the computed natural frequencies and the forcing frequency confirms the contribution of the actual spacetimeresolved measured surface. These experimental results are an accurate estimation of the influence of the additional restoring force exerted by the pinned contact line on the deformed surface which increases the wave celerity. The local character of this effect is evidenced by the decrease of the shift of the dispersion relation as a function of the channel width.


Depthtargeted energy delivery deep inside scattering media Bender, N., A. Yamilov, A. Goetschy, H. Yılmaz, C. W. Hsu, and H. Cao Nature Physics (2022)


Propagation of scalar waves in dense disordered media exhibiting short and longrange correlations Rohfritsch, A., J. M. Conoir, T. ValierBrasier, R. Pierrat, and R. Marchiano Physical Review E 104, no. 6 (2021)
Résumé: Correlated disorder is at the heart of numerous challenging problematics in physics. In this work we focus on the propagation of acoustic coherent waves in twodimensional dense disordered media exhibiting long and shortrange structural correlations. The media are obtained by inserting elastic cylinders randomly in a stealth hyperuniform medium itself made up of cylinders. The properties of the coherent wave is studied using an original numerical software. In order to understand and discuss the complex physical phenomena occurring in the different media, we also make use of effective media models derived from the quasicrystalline approximation and the theory of Fikioris and Waterman that provides an explicit expression of the effective wave numbers. Our study shows a very good agreement between numerical and homogenization models up to very high concentrations of scatterers. This study shows that media with both short and longrange correlations are of strong interest to design materials with original properties.


Modal approximation for strictly convex plasmonic resonators in the time domain: The Maxwell's equations Ammari, H., P. Millien, and A. L. Vanel Journal of Differential Equations 309, 676703 (2022)
Résumé: We study the possible expansion of the electromagnetic field scattered by a strictly convex metallic nanoparticle with dispersive material parameters placed in a homogeneous medium in a lowfrequency regime as a sum of modes oscillating at complex frequencies (diverging at infinity), known in the physics literature as the quasinormal modes expansion. We show that such an expansion is valid in the static regime and that we can approximate the electric field with a finite number of modes. We then use perturbative spectral theory to show the existence, in a certain regime, of plasmonic resonances as poles of the resolvent for Maxwell's equations with nonzero frequency. We show that, in the time domain, the electric field can be written as a sum of modes oscillating at complex frequencies. We introduce renormalised quantities that do not diverge exponentially at infinity.


Effective Model for Elastic Waves in a Substrate Supporting an Array of Plates/Beams with Flexural and Longitudinal Resonances Marigo, J. J., K. Pham, A. Maurel, and S. Guenneau Journal of Elasticity 146, no. 1, 143177 (2021)
Résumé: In a previous study (Marigo et al. in J. Mech. Phys. Solids 143:104029, 2020) we have studied the effect of a periodic array of subwavelength plates or beams over a semiinfinite elastic ground on the propagation of waves hitting the interface. The study was restricted to the low frequency regime where only flexural resonances take place. Here, we present a generalization to higher frequencies which allows us to account for both flexural and longitudinal resonances and to evaluate their interplay. An effective model is obtained using asymptotic analysis and homogenization techniques, which can be expressed in terms of the ground alone with an effective dynamic (frequencydependent) boundary conditions of the Robin’s type. For an inplane wave at oblique incidence, the scattered displacement fields and the reflection coefficients are obtained in closed forms and their effectiveness to reproduce the actual scattering is inspected by comparison with direct numerics in a twodimensional setting.


Full characterization of the transmission properties of a multiplane light converter Boucher, P., A. Goetschy, G. Sorelli, M. Walschaers, and N. Treps Physical Review Research 3, no. 2 (2021)
Résumé: Multiplane light conversion (MPLC) allows to perform arbitrary transformations on a finite set of spatial modes with no theoretical restriction to the quality of the transformation. Even though the number of shaped modes is in general small, the number of modes transmitted by an MPLC system is extremely large. In this paper, we aim to characterize the transmission properties of a multiplane light converter inside and outside the designmodes subspace. We report the construction of the full transmission matrix of such systems. By performing singular value decompositions, we individuate ways to evaluate their efficiency in performing the design transformation. Moreover, we develop an analytical random matrix model that suggests that in the regime of a large number of shaped modes an MPLC system behaves like a random scattering medium with limited number of controlled channels.


Universal Statistics of Waves in a Random TimeVarying Medium Carminati, R., H. Chen, R. Pierrat, and B. Shapiro Physical Review Letters 127, no. 9 (2021)
Résumé: We study the propagation of waves in a medium in which the wave velocity fluctuates randomly in time. We prove that at long times, the statistical distribution of the wave energy is lognormal, with the average energy growing exponentially. For weak disorder, another regime preexists at shorter times, in which the energy follows a negative exponential distribution, with an average value growing linearly with time. The theory is in perfect agreement with numerical simulations, and applies to different kinds of waves. The existence of such universal statistics bridges the fields of wave propagation in timedisordered and spacedisordered media.


Localized modes revealed in random lasers Kumar, B., R. Homri, Priyanka, S. K. Maurya, M. Lebental, and P. Sebbah Optica 8, no. 8, 10331039 (2021)
Résumé: In sufficiently strong scattering media, light transport is suppressed and modes are exponentially localized. Andersonlike localized states have long been recognized as potential candidates for highQ optical modes for lowthreshold, costeffective random lasers. Operating in this regime remains, however, a challenge since Anderson localization is difficult to achieve in optics, and nonlinear mode interaction compromises its observation. Here, we exhibit individually each lasing mode of a lowdimension solidstate random laser by applying a nonuniform optical gain. By undoing gain competition and crosssaturation, we demonstrate that all lasing modes are spatially localized.We find that selective excitation significantly reduces the lasing threshold, while lasing efficiency is greatly improved. We show further how their spatial locations are critical to boost laser power efficiency. By efficiently suppressing the spatial hole burning effect, we can turn on the optimally outcoupled random lasing modes. Our demonstration opens the road to the exploration of linear and nonlinear mode interactions in the presence of gain, as well as disorderengineering for laser applications.


Time domain modelling of a Helmholtz resonator analogue for water waves Euvé, L. P., K. Pham, P. Petitjeans, V. Pagneux, and A. Maurel Journal of Fluid Mechanics 920 (2021)
Résumé: In the context of water waves, we consider a resonator with deep subwavelength resonance, analogue to the Helmholtz resonator in acoustics. In the shallow water regime, using asymptotic analysis, a onedimensional model is derived in which the effect of the resonator is reduced to effective transmission conditions. These conditions clearly highlight two contributions. The first is associated with the dock on its own and it is responsible for a jump of the potential at the free surface. The second is due to the resonant cavity and it is responsible for a jump in the horizontal velocity. It involves as well the uniform amplitude within the resonant cavity with a transient dynamics explicitly given by the equation of a damped oscillator forced by the incident waves. The onedimensional model is validated in the harmonic regime by comparison to direct twodimensional numerics. It is shown to reproduce accurately the scattering coefficients and the amplitude within the resonator; interestingly, this remains broadly true for finite water depths. We further inspect the spatiotemporal behaviour of different types of wave packets interacting with the resonating and radiating cavity.


Control of the swell by an array of helmholtz resonators Euvé, L. P., N. Piesniewska, A. Maurel, K. Pham, P. Petitjeans, and V. Pagneux Crystals 11, no. 5, 520 (2021)
Résumé: We present a theoretical and experimental study of a resonator of the Helmholtz type for the control of the swell. An experimental demonstration of the shielding effect by a belt made of evenly distributed resonators is given. We then provide indepth analysis of the Fano resonance resulting from the interference between the dock scattering (the background) and the resonant cavity scattering. This is done thanks to spacetime resolved experiments which provides the complexvalued scattering coefficients and amplitude within the resonator. We provide a onedimensional model derived in the shallow water regime owing to asymptotic analysis. The model contains the two ingredients of the Fano resonance and allows us to exhibit the damping due to leakage. When adding heuristically the damping due to losses, it reproduces the main features of the resonance observed experimentally.


Quantitative Temperature Measurements in Gold Nanorods Using Digital Holography Lalisse, A., A. A. Mohtar, M. C. Nguyen, R. Carminati, J. Plain, and G. Tessier ACS Applied Materials and Interfaces (2021)
Résumé: © Temperature characterization and quantification at the nanoscale remain core challenges in applications based on photoinduced heating of nanoparticles. Here, we propose a new approach to obtain quantitative temperature measurements on individual nanoparticles by combining modulated photothermal stimulation and heterodyne digital holography. From fullfield reconstructed holograms, the temperature is determined with a precision of 0.3 K via a simple approach without requiring any calibration or fitting parameters. As an application, the dependence of temperature on the aspect ratio of gold nanoparticles is investigated. A good agreement with numerical simulation is observed.


A stable, unified model for resonant Faraday cages Delourme, B., E. Lunéville, J. J. Marigo, A. Maurel, J. F. Mercier, and K. Pham Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2245 (2021)
Résumé: © 2021 The Author(s). We study some effective transmission conditions able to reproduce the effect of a periodic array of Dirichlet wires on wave propagation, in particular when the array delimits an acoustic Faraday cage able to resonate. In the study of Hewett & Hewitt (2016 Proc. R. Soc. A 472, 20160062 (doi:10.1098/rspa.2016.0062)) different transmission conditions emerge from the asymptotic analysis whose validity depends on the frequency, specifically the distance to a resonance frequency of the cage. In practice, dealing with such conditions is difficult, especially if the problem is set in the time domain. In the present study, we demonstrate the validity of a simpler unified model derived in Marigo & Maurel (2016 Proc. R. Soc. A 472, 20160068 (doi:10.1098/rspa.2016.0068)), where unified means valid whatever the distance to the resonance frequencies. The effectiveness of the model is discussed in the harmonic regime owing to explicit solutions. It is also exemplified in the time domain, where a formulation guaranteeing the stability of the numerical scheme has been implemented.


Revisiting imperfect interface laws for twodimensional elastodynamics Pham, K., A. Maurel, and J. J. Marigo Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 477, no. 2245 (2021)
Résumé: © 2021 The Authors. We study the interaction of inplane elastic waves with imperfect interfaces composed of a periodic array of voids or cracks. An effective model is derived from highorder asymptotic analysis based on twoscale homogenization and matched asymptotic technique. In twodimensional elasticity, we obtain jump conditions set on the inplane displacements and normal stresses; the jumps involve in addition effective parameters provided by static, elementary problems being the equivalents of the cell problems in classical twoscale homogenization. The derivation of the model is conducted in the transient regime and its stability is guarantied by the positiveness of the effective interfacial energy. Spring models are envisioned as particular cases. It is shown that masslessspring models are recovered in the limit of small void thicknesses and collinear cracks. By contrast, the use of massspring model is justified at normal incidence, otherwise unjustified. We provide quantitative validations of our model and comparison with spring models by means of comparison with direct numerical calculations in the harmonic regime.


Quantitative Measurement of the Thermal Contact Resistance between a Glass Microsphere and a Plate Doumouro, J., E. Perros, A. Dodu, N. Rahbany, D. Leprat, V. Krachmalnicoff, R. Carminati, W. Poirier, and Y. De Wilde Physical Review Applied 15, no. 1 (2021)
Résumé: © 2021 American Physical Society. Accurate measurements of the thermal resistance between microobjects made of insulating materials are complex because of their small size, low conductivity, and the presence of various illdefined gaps. We address this issue using a modified scanning thermal microscope operating in vacuum and in air. The sphereplate geometry is considered. Under controlled heating power, we measure the temperature on top of a glass microsphere glued to the probe as it approaches a glass plate at room temperature with nanometer accuracy. In vacuum, a jump is observed at contact. From this jump in temperature and the modeling of the thermal resistance of a sphere, the sphereplate contact resistance RK=(1.4±0.18)×107KW1 and effective radius r=36±4 nm are obtained. In air, the temperature on top of the sphere shows a decrease starting from a sphereplate distance of 200μm. A jump is also observed at contact, with a reduced amplitude. The sphereplate coupling out of contact can be described by the resistance shape factor of a sphere in front of a plate in air, placed in a circuit involving a series and a parallel resistance that are determined by fitting the approach curve. The contact resistance in air RK  =(1.2±0.46)×107KW1 is then estimated from the temperature jump. The method is quantitative without requiring any tedious multiplescale numerical simulation, and is versatile to describe the coupling between microobjects from large distances to contact in various environments.


A direct linear inversion for discontinuous elastic parameters recovery from internal displacement information only Ammari, H., E. Bretin, P. Millien, and L. Seppecher Numerische Mathematik 147, no. 1, 189226 (2021)
Résumé: © 2021, The Author(s), under exclusive licence to SpringerVerlag GmbH, DE part of Springer Nature. The aim of this paper is to present and analyze a new direct method for solving the linear elasticity inverse problem. Given measurements of some displacement fields inside a medium, we show that a stable reconstruction of elastic parameters is possible, even for discontinuous parameters and without boundary information. We provide a general approach based on the weak definition of the stiffnesstoforce operator which conduces to see the problem as a linear system. We prove that in the case of shear modulus reconstruction, we have an L2 stability with only one measurement under minimal smoothness assumptions. This stability result is obtained through the proof that the linear operator to invert has closed range. We then describe a direct discretization which provides stable reconstructions of both isotropic and anisotropic stiffness tensors.


Observations of symmetryinduced topological mode steering in a reconfigurable elastic plate Tang, K., M. Makwana, R. V. Craster, and P. Sebbah Physical Review B 102, no. 21 (2020)
Résumé: © 2020 American Physical Society. We experimentally investigate the valleyHall effect for interfacial edge states, highlighting the importance of the modal patterns between geometrically distinct regions within a structured elastic plate. These experiments, for vibration, are at a scale where detailed measurements are taken throughout the system and not just at the input/output ports; this exposes the coupling between geometrically distinct modes that underlie the differences between wave transport around gentle and sharp bends.


Perfect depolarization in single scattering of light from uncorrelated surface and volume disorder Banon, J.P., I. Simonsen, and R. Carminati Optics Letters 45, no. 23, 6354 (2020)
Résumé: © 2020 Optical Society of America We demonstrate that single scattering of ppolarized waves from uncorrelated surface and volume disorder can lead to perfect depolarization. The degree of polarization vanishes in specific scattering directions that can be characterized based on simple geometric arguments. Depolarization results from a different polarization response of each source of disorder, which provides a clear physical interpretation of the depolarization mechanism.


Effective Resonant Model and Simulations in the TimeDomain of Wave Scattering from a Periodic Row of HighlyContrasted Inclusions Touboul, M., K. Pham, A. Maurel, J. J. Marigo, B. Lombard, and C. Bellis Journal of Elasticity 142, no. 1, 5382 (2020)
Résumé: © 2020, Springer Nature B.V. The timedomain propagation of scalar waves across a periodic row of inclusions is considered in 2D. As the typical wavelength within the background medium is assumed to be much larger than the spacing between inclusions and the row width, the physical configuration considered is in the lowfrequency homogenization regime. Furthermore, a high contrast between one of the constitutive moduli of the inclusions and of the background medium is also assumed. So the wavelength within the inclusions is of the order of their typical size, which can further induce local resonances within the microstructure. In Pham et al. (J. Mech. Phys. Solids 106:80–94, 2017), twoscale homogenization techniques and matchedasymptotic expansions have been employed to derive, in the harmonic regime, effective jump conditions on an equivalent interface. This homogenized model is frequencydependent due to the resonant behavior of the inclusions. In this context, the present article aims at investigating, directly in the timedomain, the scattering of waves by such a periodic row of resonant scatterers. Its effective behavior is first derived in the timedomain and some energy properties of the resulting homogenized model are analyzed. Timedomain numerical simulations are then performed to illustrate the main features of the effective interface model obtained and to assess its relevance in comparison with fullfield simulations.


Absorption of scalar waves in correlated disordered media and its maximization using stealth hyperuniformity Sheremet, A., R. Pierrat, and R. Carminati Physical Review A 101, no. 5, 053829 (2020)


Effective model for elastic waves propagating in a substrate supporting a dense array of plates/beams with flexural resonances Marigo, J.J., K. Pham, A. Maurel, and S. Guenneau Journal of the Mechanics and Physics of Solids 143 (2020)
Résumé: © 2020 We consider the effect of an array of plates or beams over a semiinfinite elastic ground on the propagation of elastic waves hitting the interface. The plates/beams are slender bodies with flexural resonances at low frequencies able to perturb significantly the propagation of waves in the ground. An effective model is obtained using asymptotic analysis and homogenization techniques, which can be expressed in terms of the ground alone with effective dynamic (frequencydependent) boundary conditions of the Robin's type. For an incident plane wave at oblique incidence, the displacement fields and the reflection coefficients are obtained in closed forms and their validity is inspected by comparison with direct numerics in a twodimensional setting.
Motsclés: Asymptotic analysis; Elastic waves; Metamaterials; Metasurfaces; Multimodal method


Origin of transparency in scattering biomimetic collagen materials Salameh, C., F. Salviat, E. Bessot, M. Lama, J.M. Chassot, E. Moulongui, Y. Wang, M. Robin, A. Bardouil, M. Selmane, F. Artzner, A. Marcellan, C. Sanchez, M.M. GiraudGuille, M. Faustini, R. Carminati, and N. Nassif Proceedings of the National Academy of Sciences of the United States of America 117, no. 22, 1194711953 (2020)
Résumé: Living tissues, heterogeneous at the microscale, usually scatter light. Strong scattering is responsible for the whiteness of bones, teeth, and brain and is known to limit severely the performances of biomedical optical imaging. Transparency is also found within collagenbased extracellular tissues such as decalcified ivory, fish scales, or cornea. However, its physical origin is still poorly understood. Here, we unveil the presence of a gap of transparency in scattering fibrillar collagen matrices within a narrow range of concentration in the phase diagram. This precholesteric phase presents a threedimensional (3D) orientational order biomimetic of that in natural tissues. By quantitatively studying the relation between the 3D fibrillar network and the optical and mechanical properties of the macroscopic matrices, we show that transparency results from structural partial order inhibiting light scattering, while preserving mechanical stability, stiffness, and nonlinearity. The striking similarities between synthetic and natural materials provide insights for better understanding the occurring transparency.
Motsclés: collagen; mechanical properties; photonic materials; selfassembly; transparency


Single scattering of polarized light by correlated surface and volume disorder Banon, J.P., I. Simonsen, and R. Carminati Physical Review A 101, no. 5 (2020)
Résumé: © 2020 American Physical Society. We study light scattering by systems combining randomly rough surface and volume dielectric fluctuations. We introduce a general model including correlations between surface and volume disorders, and we study the scattering properties within a singlescattering approach. We identify different regimes of surface and volume dominated scattering depending on length scales characterizing the surface and volume disorders. For uncorrelated disorders, we discuss the polarization response of each source of disorder, and show how polarimetric measurements can be used to separate the surface and volume contributions in the total measured diffusely scattered intensity. For correlated systems, we identify two configurations of volume disorder which, respectively, couple weakly or strongly to surface scattering via surfacevolume cross correlations. We illustrate these effects on different configurations exhibiting interference patterns in the diffusely scattered intensity, which may be of interest for the characterization of complex systems or for the design of optical components by engineering the degree of surfacevolume correlations.


Influence of the Local Scattering Environment on the Localization Precision of Single Particles Bouchet, D., R. Carminati, and A. P. Mosk Physical Review Letters 124, no. 13, 133903 (2020)
Résumé: We study the fundamental limit on the localization precision for a subwavelength scatterer embedded in a strongly scattering environment, using the external degrees of freedom provided by wavefront shaping. For a weakly scattering target, the localization precision improves with the value of the local density of states at the target position. For a strongly scattering target, the localization precision depends on the dressed polarizability that includes the backaction of the environment. This numerical study provides new insights for the control of the information content of scattered light by wavefront shaping, with potential applications in sensing, imaging, and nanoscale engineering.


Hybridized love waves in a guiding layer supporting an array of plates with decorative endings Pham, K., A. Maurel, S. Félix, and S. Guenneau Materials 13, no. 7, 1632 (2020)
Résumé: © 2020 by the authors. This study follows from Maurel et al., Phys. Rev. B 98, 134311 (2018), where we reported on direct numerical observations of outofplane shear surface waves propagating along an array of plates atop a guiding layer, as a model for a forest of trees. We derived closed form dispersion relations using the homogenization procedure and investigated the effect of heterogeneities at the top of the plates (the foliage of trees). Here, we extend the study to the derivation of a homogenized model accounting for heterogeneities at both endings of the plates. The derivation is presented in the time domain, which allows for an energetic analysis of the effective problem. The effect of these heterogeneous endings on the properties of the surface waves is inspected for hard heterogeneities. It is shown that top heterogeneities affect the resonances of the plates, hence modifying the cutoff frequencies of a wave mathematically similar to the socalled Spoof Plasmon Polariton (SPP) wave, while the bottom heterogeneities affect the behavior of the layer, hence modifying the dispersion relation of the Love waves. The complete system simply mixes these two ingredients, resulting in hybrid surface waves accurately described by our model.
Motsclés: Elastic energy; Elastic metasurface; Homogenization; Metamaterial; Time domain analysis


Measuring cell displacements in opaque tissues: dynamic light scattering in the multiple scattering regime Brunel, B., V. Levy, A. Millet, M. E. Dolega, A. Delon, R. Pierrat, and G. Cappello Biomedical Optics Express 11, no. 4, 2277 (2020)


Multimodal method for the scattering by an array of plates connected to an elastic halfspace Maurel, A., and K. Pham Journal of the Acoustical Society of America 146, no. 6, 44024412 (2019)
Résumé: © 2019 Acoustical Society of America. An accurate and numerically inexpensive method is presented to calculate the reflection of inplane waves at the free surface of an elastic substrate supporting a periodic array of plates. The method is based on the expansions of the elastic fields on the pseudoperiodic modes in the substrate and on the Lamb modes in the plates. These expansions involve unknown amplitudes which are determined by simple matrix inversion when accounting for the boundary conditions at the surface of the substrate and at the free edges of the plates. Exemplifying results are reported in a wide range of frequency covering two resonances of the plates which are analyzed: a flexural resonance of slender bodies and the quasiresonance of the socalled edge mode. The convergence of the method is inspected quantitatively; it is shown that it is good in view of the fact that the stress is singular at the corners of the plates in contact with the substrate. In particular, the scattering coefficients converge as 1/N s 3/2 with N s the truncation of the expansions.


Optimizing Light Storage in Scattering Media with the DwellTime Operator Durand, M., S. M. Popoff, R. Carminati, and A. Goetschy Physical Review Letters 123, no. 24 (2019)
Résumé: © 2019 American Physical Society. We prove that optimal control of light energy storage in disordered media can be reached by wave front shaping. For this purpose, we build an operator for dwell times from the scattering matrix and characterize its full eigenvalue distribution both numerically and analytically in the diffusive regime, where the thickness L of the medium is much larger than the mean free path â.,". We show that the distribution has a finite support with a maximal dwell time larger than the most likely value by a factor (L/â.,")2≫1. This reveals that the highest dwelltime eigenstates deposit more energy than the open channels of the medium. Finally, we show that the dwelltime operator can be used to store energy in resonant targets buried in complex media, without any need for guide stars.


Perfect Brewster transmission through ultrathin perforated films Pham, K., A. Maurel, J. F. Mercier, S. Félix, M. L. Cordero, and C. Horvath Wave Motion 93 (2020)
Résumé: © 2019 We address the perfect transmission of a plane acoustic wave at oblique incidence on a perforated, sound penetrable or rigid, film in twodimensions. It is shown that the Brewster incidence θ∗ realizing socalled extraordinary transmission due to matched impedances varies significantly when the thickness e of the film decreases. For thick films, i.e. ke≫1 with k the incident wavenumber, the classical effective medium model provides an accurate prediction of the Brewster angle independent of e (this Brewster angle is denoted θB). However, for thinner films with ke<1, θ∗ becomes dependent of e and it deviates from θB. To properly describe this shift, an interface model is used (Marigo et al., 2017) which accurately reproduces the spectra of ultrathin to relatively thick perforated films. Depending on the contrasts in the material properties of the film and of the surrounding matrix, decreasing the film thickness can produce an increase or a decrease of θ∗; it can also produce the disappearance of a perfect transmission or to the contrary its appearance.


Angular Memory Effect of Transmission Eigenchannels Yllmaz, H., C. W. Hsu, A. Goetschy, S. Bittner, S. Rotter, A. Yamilov, and H. Cao Physical Review Letters 123, no. 20 (2019)
Résumé: © 2019 American Physical Society. The optical memory effect has emerged as a powerful tool for imaging through multiplescattering media; however, the finite angular range of the memory effect limits the field of view. Here, we demonstrate experimentally that selective coupling of incident light into a hightransmission channel increases the angular memoryeffect range. This enhancement is attributed to the robustness of the hightransmission channels against perturbations such as sample tilt or wave front tilt. Our work shows that the hightransmission channels provide an enhanced field of view for memoryeffectbased imaging through diffusive media.


Scattering of gravity waves by a periodically structured ridge of finite extent Maurel, A., K. Pham, and J. J. Marigo Journal of Fluid Mechanics 871, 350376 (2019)
Résumé: © 2019 Cambridge University Press. We study the propagation of water waves over a ridge structured at the subwavelength scale using homogenization techniques able to account for its finite extent. The calculations are conducted in the time domain considering the full threedimensional problem to capture the effects of the evanescent field in the water channel over the structured ridge and at its boundaries. This provides an effective twodimensional wave equation which is a classical result but also nonintuitive transmission conditions between the region of the ridge and the surrounding regions of constant immersion depth. Numerical results provide evidence that the scattering properties of a structured ridge can be strongly influenced by the evanescent fields, a fact which is accurately captured by the homogenized model.
Motsclés: shallow water flows; surface gravity waves; wavestructure interactions


Blind ghost imaging PaniaguaDiaz, A. M., I. Starshynov, N. Fayard, A. Goetschy, R. Pierrat, R. Carminati, and J. Bertolotti Optica 6, no. 4, 460464 (2019)
Résumé: © 2019 Optical Society of America. Ghost imaging is an unconventional optical imaging technique that reconstructs the shape of an object by combining the measurement of two signals: one that interacted with the object, but without any spatial information; the other containing spatial information, but that never interacted with the object. Here we demonstrate that ghost imaging can be performed without ever knowing the patterns that illuminate the object, by instead using patterns correlated with them, no matter how weakly. As an experimental proof, we reconstruct the image of an object hidden behind a scattering layer using only the reflected light, which never interacts with the object.


Enhanced resonance of sparse arrays of Helmholtz resonators  Application to perfect absorption Maurel, A., J. F. Mercier, K. Pham, J. J. Marigo, and A. Ourir Journal of the Acoustical Society of America 145, no. 4, 25522560 (2019)
Résumé: © 2019 Acoustical Society of America. The influence of the spacing on the resonance of a periodic arrangement of Helmholtz resonators is inspected. An effective problem is used which accurately captures the properties of the resonant array within a large range of frequencies, and whose simplified version leaves an impedance condition. It is shown that the strength of the resonance is enhanced when the array becomes sparser. This degree of freedom on the radiative damping is of particular interest since it does not affect the resonance frequency nor the damping due to losses within each resonator; in addition, it does not affect the total thickness of the array. It is shown that it can be used for the design of a perfect absorbing wall.


Coherent light propagation through cold atomic clouds beyond the independent scattering approximation Kwong, C. C., D. Wilkowski, D. Delande, and R. Pierrat Physical Review A 99, no. 4 (2019)
Résumé: © 2019 American Physical Society. We calculate the relative permittivity of a cold atomic gas under weak probe illumination, up to second order in the density. Within the framework of a diagrammatic representation method, we identify all the secondorder diagrams that enter into the description of the relative permittivity for coherent light transmission. These diagrams originate from pairwise position correlation and recurrent scattering. Using coupled dipole equations, we numerically simulate the coherent transmission with scalar and vector waves and find good agreement with the perturbative calculations. We applied this perturbative expansion approach to a classical gas at rest, but the method is extendable to thermal gas with finite atomic motion and to quantum gases where nontrivial pair correlations can be naturally included.


Enhanced absorption of waves in stealth hyperuniform disordered media Bigourdan, F., R. Pierrat, and R. Carminati Optics Express 27, no. 6, 86668682 (2019)
Résumé: © 2019 Optical Society of America We study the propagation of waves in a set of absorbing subwavelength scatterers positioned on a stealth hyperuniform point pattern. We show that spatial correlations in the disorder substantially enhance absorption compared to a fully disordered structure with the same density of scatterers. The nonresonant nature of the mechanism provides broad angular and spectral robustness. These results demonstrate the possibility to design lowdensity materials with blackbodylike absorption.


Terahertz and Visible Probing of Particles Suspended in Air Prophete, C., H. Sik, E. Kling, R. Carminati, and J. De Rosny IEEE Transactions on Terahertz Science and Technology 9, no. 2, 120125 (2019)
Résumé: © 20112012 IEEE. The attenuation of air suspended particles is measured with a terahertz (THz) timedomain spectrometer. Simultaneously, the attenuation at a wavelength of 650 nm is probed with a laser diode. On the one hand, this dual measurement allows a direct assessment of the visibility evolution in the THz range compared to the visible range. On the other hand, this setup provides an estimation of the scattering strength and the density of particles. Using the Mie theory, the method is successfully applied to experimentally characterize the refractive index of sand grains and glass beads. The refractive indexes of sand grains and glass beads, average over the acquisitions, are 1.67 and 2.54, respectively. The estimation of the scattering properties of sand grains is crucial to evaluate the performance of THz systems to image through brownout clouds that are created by helicopter rotors when landing in arid areas.
Motsclés: Propagation; refractive index; terahertz (THz) scattering; THz timedomain spectroscopy (THzTDS)


Quantum dipole emitters in structured environments: A scattering approach: Tutorial Bouchet, D., and R. Carminati Journal of the Optical Society of America A: Optics and Image Science, and Vision 36, no. 2, 186195 (2019)
Résumé: © 2019 Optical Society of America. We provide a simple semiclassical formalism to describe the coupling between one or several quantum emitters and a structured environment. Describing the emitter by an electric polarizability, and the surrounding medium by a Green function, we show that an intuitive scattering picture allows one to derive a coupling equation from which the eigenfrequencies of the coupled system can be extracted. The model covers a variety of regimes observed in light–matter interaction, including weak and strong coupling, coherent collective interactions, and incoherent energy transfer. It provides a unified description of many processes, showing that different interaction regimes are actually rooted on the same ground. It can also serve as a basis for the development of more refined models in a full quantum electrodynamics framework.


Cross density of states and mode connectivity: Probing wave localization in complex media CanaguierDurand, A., R. Pierrat, and R. Carminati Physical Review A 99, no. 1 (2019)
Résumé: © 2019 American Physical Society. We introduce the mode connectivity as a measure of the number of eigenmodes of a wave equation connecting two points at a given frequency. Based on numerical simulations of scattering of electromagnetic waves in disordered media, we show that the connectivity discriminates between the diffusive and the Anderson localized regimes. For practical measurements, the connectivity is encoded in the secondorder coherence function characterizing the intensity emitted by two incoherent classical or quantum dipole sources. The analysis applies to all processes in which spatially localized modes build up, and to all kinds of waves.


Perfect absorption of water waves by linear or nonlinear critical coupling Monsalve, E., A. Maurel, P. Petitjeans, and V. Pagneux Applied Physics Letters 114, no. 1 (2019)
Résumé: © 2019 Author(s). We report on experiments of perfect absorption for surface gravity waves impinging a wall structured by a subwavelength resonator. By tuning the geometry of the resonator, a balance is achieved between the radiation damping and the intrinsic viscous damping, resulting in perfect absorption by critical coupling. Besides, it is shown that the resistance of the resonator, hence the intrinsic damping, can be controlled by the wave amplitude, which provides a way for perfect absorption tuned by nonlinear mechanisms. The perfect absorber that we propose, without moving parts or added material, is simple and robust and presents a deeply subwavelength ratio wavelength/thickness of 18.


Conversion of Love waves in a forest of trees Maurel, A., J. J. Marigo, K. Pham, and S. Guenneau Physical Review B 98, no. 13 (2018)
Résumé: © 2018 American Physical Society. We inspect the propagation of shear polarized surface waves akin to Love waves through a forest of trees of the same height atop a guiding layer on a soil substrate. An asymptotic analysis shows that the forest behaves like an infinitely anisotropic wedge with effective boundary conditions. We discover that the foliage of trees brings a radical change in the nature of the dispersion relation of these surface waves, which behave like spoof plasmons in the limit of a vanishing guiding layer, and like Love waves in the limit of trees with a vanishing height. When we consider a forest with trees of increasing or decreasing height, this hybrid "spoof Love wave" is either trapped within the trees or converted into a downward propagating bulk (shear) wave. These mechanisms of wave trapping and wave conversion appear to be robust with respect to perturbations of height or position of trees in the metawedge and with respect to threedimensional effects such as regarding a potential change of elastic wave polarization.


Sensitivity of a dielectric layered structure on a scale below the periodicity: A fully local homogenized model Maurel, A., and J. J. Marigo Physical Review B 98, no. 2 (2018)
Résumé: © 2018 American Physical Society. We inspect the unusual scattering properties reported recently for structures alternating dielectric layers of subwavelength thicknesses near the critical angle for total reflection. In TE polarization, the unusual scattering properties are captured by an effective model with an accuracy less than 1% up to kd∼0.1. It is shown that the propagation is simply dispersive with local dispersion while the boundary layer effects are captured through a nonintuitive transmission condition. The resulting model involves two parameters depending only on the characteristics of the multilayer and which are given in closed forms. Besides, we show that a discrete description of the spectrum using the layer thickness d as unit of measure misses the complexity of the continuous spectrum exhibiting strong variations within the scale d. This ultrasensitivity to variations below d is attributable to strong boundary layer effects and, for large structures, to a cooperation between the boundaries and the phase accumulation within the structure.


Modeling of an active terahertz imaging system in brownout conditions Prophète, C., R. Pierrat, H. Sik, E. Kling, R. Carminati, and J. De Rosny Applied Optics 57, no. 21, 60176026 (2018)
Résumé: © 2018 Optical Society of America. We present a theoretical evaluation of a subterahertz (subTHz) system to image through a scattering medium composed of scatterers of sizes close to the wavelength. We specifically study the case of sand grain clouds created by helicopter rotor airflow during landing in arid areas. The different powers received by one pixel of a matrix made of subTHz sensors are identified. Photometric and antennabased sensors are considered. Besides the thermal contribution to the noise, we focus our attention on the radiation backscattered by the brownout. It appears that a configuration where the source and the camera are distant is the most promising configuration and is realistic for embedded systems.


Photon echoes in strongly scattering media: A diagrammatic approach Pierrat, R., R. Carminati, and J. L. Le Gouët Physical Review A 97, no. 6 (2018)
Résumé: © 2018 American Physical Society. We study photon echo generation in disordered media with the help of multiple scattering theory based on diagrammatic approach and numerical simulations. We show that a strong correlation exists between the driving fields at the origin of the echo and the echo beam. Opening the way to a better understanding of nonlinear wave propagation in complex materials, this work supports recent experimental results with applications to the measurement of the optical dipole lifetime T2 in powders.


NonGaussian Correlations between Reflected and Transmitted Intensity Patterns Emerging from Opaque Disordered Media Starshynov, I., A. M. PaniaguaDiaz, N. Fayard, A. Goetschy, R. Pierrat, R. Carminati, and J. Bertolotti Physical Review X 8, no. 2 (2018)
Résumé: © 2018 authors. Published by the American Physical Society. The propagation of monochromatic light through a scattering medium produces speckle patterns in reflection and transmission, and the apparent randomness of these patterns prevents direct imaging through thick turbid media. Yet, since elastic multiple scattering is fundamentally a linear and deterministic process, information is not lost but distributed among many degrees of freedom that can be resolved and manipulated. Here, we demonstrate experimentally that the reflected and transmitted speckle patterns are robustly correlated, and we unravel all the complex and unexpected features of this fundamentally nonGaussian and longrange correlation. In particular, we show that it is preserved even for opaque media with thickness much larger than the scattering mean free path, proving that information survives the multiple scattering process and can be recovered. The existence of correlations between the two sides of a scattering medium opens up new possibilities for the control of transmitted light without any feedback from the target side, but using only information gathered from the reflected speckle.


Backscattering reduction for resonating obstacle in waterwave channel Bobinski, T., A. Maurel, P. Petitjeans, and V. Pagneux Journal of Fluid Mechanics 845, R4 (2018)
Résumé: © 2018 Cambridge University Press. We consider the propagation of water waves in a waveguide with a surfacepiercing circular cylinder. A plane wave interacting with the cylinder leads to a Fano resonance resulting in strong scattering with a large reflection coefficient. Using a smoothly varying bathymetry whose shape is optimized, we show both numerically and experimentally that broadband and robust backscattering reduction can be obtained below the first cutoff frequency.
Motsclés: surface gravity waves; wave scattering; waves/freesurface flows


OneShot Measurement of the ThreeDimensional Electromagnetic Field Scattered by a Subwavelength Aperture Tip Coupled to the Environment Rahbany, N., I. Izeddin, V. Krachmalnicoff, R. Carminati, G. Tessier, and Y. De Wilde ACS Photonics 5, no. 4, 15391545 (2018)
Résumé: © 2018 American Chemical Society. Nearfield scanning optical microscopy (NSOM) achieves subwavelength resolution by bringing a nanosized probe close to the surface of the sample. This extends the spectrum of spatial frequencies that can be detected with respect to a diffraction limited microscope. The interaction of the probe with the sample is expected to affect its radiation to the far field in a way that is often hard to predict. Here we address this question by proposing a general method based on fullfield offaxis digital holography microscopy which enables to study in detail the farfield radiation from a NSOM probe as a function of its environment. A first application is demonstrated by performing a threedimensional (3D) tomographic reconstruction of light scattered from the subwavelength aperture tip of a NSOM, in free space or coupled to transparent and plasmonic media. A single holographic image recorded in one shot in the far field contains information on both the amplitude and the phase of the scattered light. This is sufficient to reverse numerically the propagation of the electromagnetic field all the way to the aperture tip. Finite Difference Time Domain (FDTD) simulations are performed to compare the experimental results with a superposition of magnetic and electric dipole radiation.


Mutual Information between Reflected and Transmitted Speckle Images Fayard, N., A. Goetschy, R. Pierrat, and R. Carminati Physical Review Letters 120, no. 7 (2018)
Résumé: © 2018 American Physical Society. We study theoretically the mutual information between reflected and transmitted speckle patterns produced by wave scattering from disordered media. The mutual information between the two speckle images recorded on an array of N detection points (pixels) takes the form of longrange intensity correlation loops that we evaluate explicitly as a function of the disorder strength and the Thouless number g. Our analysis, supported by extensive numerical simulations, reveals a competing effect of crosssample and surface spatial correlations. An optimal distance between pixels is proven to exist that enhances the mutual information by a factor Ng compared to the singlepixel scenario.


Influence of the neck shape for Helmholtz resonators Mercier, J. F., J. J. Marigo, and A. Maurel Journal of the Acoustical Society of America 142, no. 6, 37033714 (2017)
Résumé: © 2017 Acoustical Society of America. The resonance of a Helmholtz resonator is studied with a focus on the influence of the neck shape. This is done using a homogenization approach developed for an array of resonators, and the resonance of an array is discussed when compared to that of a single resonator. The homogenization makes a parameter B appear which determines unambiguously the resonance frequency of any neck. As expected, this parameter depends on the length and on the minimum opening of the neck, and it is shown to depend also on the surface of air inside the neck. Once these three geometrical parameters are known, B has an additional but weak dependence on the neck shape, with explicit bounds.


Determination of the bottom deformation from space and timeresolved water wave measurements Cobelli, P. J., P. Petitjeans, A. Maurel, and V. Pagneux Journal of Fluid Mechanics 835, 301326 (2018)
Résumé: © 2017 Cambridge University Press. In this paper we study both theoretically and experimentally the inverse problem of indirectly measuring the shape of a localized bottom deformation with a noninstantaneous time evolution, from either an instantaneous global state (spacebased inversion) or a local timehistory record (timebased inversion) of the freesurface evolution. Firstly, the mathematical inversion problem is explicitly defined and uniqueness of its solution is established. We then show that this problem is illposed in the sense of Hadamard, rendering its solution unstable. In order to overcome this difficulty, we introduce a regularization scheme as well as a strategy for choosing the optimal value of the associated regularization parameter. We then conduct a series of laboratory experiments in which an axisymmetric threedimensional bottom deformation of controlled shape and time evolution is imposed on a layer of water of constant depth, initially at rest. The detailed evolution of the airliquid interface is measured by means of a freesurface profilometry technique providing space and timeresolved data. Based on these experimental data and employing our regularization scheme, we are able to show that it is indeed possible to reconstruct the seabed profile responsible for the linear freesurface dynamics either by space or timebased inversions. Furthermore, we discuss the different relative advantages of each type of reconstruction, their associated errors and the limitations of the inverse determination.
Motsclés: surface gravity waves; waves/freesurface flows


Optimizing Hyperuniformity in SelfAssembled Bidisperse Emulsions Ricouvier, J., R. Pierrat, R. Carminati, P. Tabeling, and P. Yazhgur Physical Review Letters 119, no. 20 (2017)
Résumé: © 2017 American Physical Society. We study long range density fluctuations (hyperuniformity) in twodimensional jammed packings of bidisperse droplets. Taking advantage of microfluidics, we systematically span a large range of size and concentration ratios of the two droplet populations. We identify various defects increasing long range density fluctuations mainly due to organization of local particle environment. By choosing an appropriate bidispersity, we fabricate materials with a high level of hyperuniformity. Interesting transparency properties of these optimized materials are established based on numerical simulations.


Observation of mean path length invariance in lightscattering media Savo, R., R. Pierrat, U. Najar, R. Carminati, S. Rotter, and S. Gigan Science 358, no. 6364, 765768 (2017)
Résumé: © 2017, American Association for the Advancement of Science. All rights reserved. The microstructure of a medium strongly influences how light propagates through it. The amount of disorder it contains determines whether the medium is transparent or opaque. Theory predicts that exciting such a medium homogeneously and isotropically makes some of its optical properties depend only on the medium’s outer geometry. Here, we report an optical experiment demonstrating that the mean path length of light is invariant with respect to the microstructure of the medium it scatters through. Using colloidal solutions with varying concentration and particle size, the invariance of the mean path length is observed over nearly two orders of magnitude in scattering strength. Our results can be extended to a wide range of systems—however ordered, correlated, or disordered—and apply to all wavescattering problems.


Effect of microstructural elongation on backscattered field: Intensity measurement and multiple scattering estimation with a linear transducer array Baelde, A., J. Laurent, P. Millien, R. Coulette, W. B. Khalifa, F. Jenson, F. Sun, M. Fink, and C. Prada Ultrasonics 82, 379389 (2018)
Résumé: © 2017 Elsevier B.V. The effect of microstructural elongation on ultrasonic backscattered fields was studied. Two methods for determining the elongation direction of macrozones in titanium alloys, using the anisotropic spatial coherence of the backscattered field, are presented. Both methods use a phased array attached on a rotative holder that records the array response matrix at several angles. Two titanium alloys were investigated: TA6V and Ti17. TA6V exhibited a strong macrozone elongation, whereas Ti17 macrozones were found equiaxial. The first method is based on the measurement of backscattered intensity in function of the probe angle relative to the macrozones elongation direction. An angular dependence of backscattered intensity is observed in presence of elongated scatterers, and their elongation direction is collinear with the probe direction corresponding to a minimal intensity. This variability is linked to both piezoelectric shape and the backscattered field spatial properties. The second method is based on the measurement of the relative proportion of single to multiple scattering in a diffusive media, using a simplified version of the single scattering filter developed in Aubry and Derode (2009). It allows the measurement of the level of multiple scattering: both titanium alloys exhibited strong multiple scattering. The elongation direction was determined as the direction of minimal multiple scattering. Furthermore, these results were confirmed by the measurement of the coherent backscattering cone on both samples.


Manipulating light at subwavelength scale by exploiting defectguided spoof plasmon modes Ourir, A., A. Maurel, S. Félix, J. F. Mercier, and M. Fink Physical Review B 96, no. 12 (2017)
Résumé: © 2017 American Physical Society. We study the defectguided modes supported by a set of metallic rods structured at the subwavelength scale. Following the idea of photonic crystal waveguide, we show that spoof plasmon surface waves can be manipulated at subwavelength scale. We demonstrate that these waves can propagate without leakage along a row of rods having a different length than the surrounding medium and we provide the corresponding dispersion relation. The principle of this subwavelength colored guide is validated experimentally. This allows us to propose the design of a wavelength demultiplexer whose efficiency is illustrated in the microwave regime.


Structure and dynamics of multicellular assemblies measured by coherent light scattering Brunel, B., C. Blanch, A. Gourrier, V. Petrolli, A. Delon, J. F. Joanny, R. Carminati, R. Pierrat, and G. Cappello New Journal of Physics 19, no. 7 (2017)
Résumé: © 2017 IOP Publishing Ltd and Deutsche Physikalische Gesellschaft. Determining the structure and the internal dynamics of tissues is essential to understand their functional organization. Microscopy allows for monitoring positions and trajectories of every single cell. Those data are useful to extract statistical observables, such as intercellular distance, tissue symm etry and anisotropy, and cell motility. However, this procedure requires a large and supervised computational effort. In addition, due to the large crosssection of cells, the light scattering limits the use of microscopy to relatively thin samples. As an alternative approach, we propose to take advantage of light scattering and to analyze the dynamical diffraction pattern produced by a living tissue illuminated with coherent light. In this article, we illustrate with a few examples that supracellular structures produce an exploitable diffraction signal. From the diffraction signal, we deduce the mean distance between cells, the anisotropy of the supracellular organization and, from its fluctuations, the mean speed of moving cells. This easy to implement technique considerably reduces analysis time, allowing real time monitoring.
Motsclés: coherent optics; dynamic light scattering; multicellular structures


Unveiling Extreme Anisotropy in Elastic Structured Media Lefebvre, G., T. Antonakakis, Y. Achaoui, R. V. Craster, S. Guenneau, and P. Sebbah Physical Review Letters 118, no. 25 (2017)


Two scale homogenization of a row of locally resonant inclusions  the case of antiplane shear waves Pham, K., A. Maurel, and J. J. Marigo Journal of the Mechanics and Physics of Solids 106, 8094 (2017)
Résumé: © 2017We present a homogenization model for a single row of locally resonant inclusions. The resonances, of the Mie type, result from a high contrast in the shear modulus between the inclusions and the elastic matrix. The presented homogenization model is based on a matched asymptotic expansion technique; it slightly differs from the classical homogenization which applies for thick arrays with many rows of inclusions (and thick means large compared to the wavelength in the matrix). Instead of the effective bulk parameters found in the classical homogenization, we end up with interface parameters entering in jump conditions for the displacement and for the normal stress; among these parameters, one is frequency dependent and encapsulates the resonant behavior of the inclusions. Our homogenized model is validated by comparison with results of full wave calculations. It is shown to be efficient in the low frequency domain and accurately describes the effects of the losses in the soft inclusions.


Quantum revival for elastic waves in thin plate Dubois, M., G. Lefebvre, and P. Sebbah European Physical Journal: Special Topics 226, no. 7, 15931601 (2017)
Résumé: © 2017, The Author(s).Quantum revival is described as the timeperiodic reconstruction of a wave packet initially localized in space and time. This effect is expected in finitesize systems which exhibit commensurable discrete spectrum such as the infinite quantum well. Here, we report on the experimental observation of full and fractional quantum revival for classical waves in a two dimensional cavity. We consider flexural waves propagating in thin plates, as their quadratic dispersion at low frequencies mimics the dispersion relation of quantum systems governed by Schrödinger equation. Timedependent excitation and measurement are performed at ultrasonic frequencies and reveal a periodic reconstruction of the initial elastic wave packet.


Spatial correlations of the spontaneous decay rate as a probe of dense and correlated disordered materials Leseur, O., R. Pierrat, and R. Carminati European Physical Journal: Special Topics 226, no. 7, 14231432 (2017)
Résumé: © 2017, The Author(s).We study theoretically and numerically a new kind of spatial correlation for waves in disordered media. We define CΓ as the correlation function of the fluorescent decay rate of an emitter at two different positions inside the medium. We show that the amplitude and the width of CΓ provide decoupled information on the structural correlation of the disordered medium and on the local environment of the emitter. This result may stimulate the emergence of new imaging and sensing modalities in complex media.


Correlationenhanced control of wave focusing in disordered media Hsu, C. W., S. F. Liew, A. Goetschy, H. Cao, and A. Douglas Stone Nature Physics 13, no. 5, 497502 (2017)
Résumé: A fundamental challenge in physics is controlling the propagation of waves in disordered media despite strong scattering from inhomogeneities. Spatial light modulators enable one to synthesize (shape) the incident wavefront, optimizing the multipath interference to achieve a specific behaviour such as focusing light to a target region. However, the extent of achievable control is not known when the target region is much larger than the wavelength and contains many speckles. Here we show that for targets containing more than g speckles, where g is the dimensionless conductance, the extent of transmission control is substantially enhanced by the longrange mesoscopic correlations among the speckles. Using a filtered random matrix ensemble appropriate for coherent diffusion in open geometries, we predict the full distributions of transmission eigenvalues as well as universal scaling laws for statistical properties, in excellent agreement with our experiment. This work provides a general framework for describing wavefrontshaping experiments in disordered systems.


Causality, Nonlocality, and Negative Refraction Forcella, D., C. Prada, and R. Carminati Physical Review Letters 118, no. 13 (2017)
Résumé: © 2017 American Physical Society. American Physical Society.The importance of spatial nonlocality in the description of negative refraction in electromagnetic materials has been put forward recently. We develop a theory of negative refraction in homogeneous and isotropic media, based on first principles, and that includes nonlocality in its full generality. The theory shows that both dissipation and spatial nonlocality are necessary conditions for the existence of negative refraction. It also provides a sufficient condition in materials with weak spatial nonlocality. These fundamental results should have broad implications in the theoretical and practical analyses of negative refraction of electromagnetic and other kinds of waves.


Correlated blinking of fluorescent emitters mediated by single plasmons Bouchet, D., E. Lhuillier, S. Ithurria, A. Gulinatti, I. Rech, R. Carminati, Y. De Wilde, and V. Krachmalnicoff Physical Review A  Atomic, Molecular, and Optical Physics 95, no. 3 (2017)
Résumé: © 2017 American Physical Society.We observe timecorrelated emission between a single CdSe/CdS/ZnS quantum dot exhibiting singlephoton statistics and a fluorescent nanobead located micrometers apart. This is accomplished by coupling both emitters to a silver nanowire. Single plasmons are created on the latter from the quantum dot, and transfer energy to excite in turn the fluorescent nanobead. We demonstrate that the molecules inside the bead show the same blinking behavior as the quantum dot.


Temperature of a nanoparticle above a substrate under radiative heating and cooling Kallel, H., R. Carminati, and K. Joulain Physical Review B  Condensed Matter and Materials Physics 95, no. 11 (2017)
Résumé: © 2017 American Physical Society.Controlling the temperature in architectures involving nanoparticles and substrates is a key issue for applications involving micro and nanoscale heat transfer. We study the thermal behavior of a single nanoparticle interacting with a flat substrate under external monochromatic illumination, and with thermal radiation as the unique heat loss channel. We develop a model to compute the temperature of the nanoparticle, based on an effective dipolepolarizability approach. Using numerical simulations, we thoroughly investigate the impacts of various parameters affecting the nanoparticle temperature, such as the nanoparticletosubstrate gap distance, the incident light wavelength and polarization, or the material resonances. This study provides a tool for the thermal characterization and design of micro or nanoscale systems coupling substrates with nanoparticles or optical antennas.


LightMediated Cascaded Locking of Multiple NanoOptomechanical Oscillators GilSantos, E., M. Labousse, C. Baker, A. Goetschy, W. Hease, C. Gomez, A. Lemaître, G. Leo, C. Ciuti, and I. Favero Physical Review Letters 118, no. 6 (2017)
Résumé: © 2017 American Physical Society.Collective phenomena emerging from nonlinear interactions between multiple oscillators, such as synchronization and frequency locking, find applications in a wide variety of fields. Optomechanical resonators, which are intrinsically nonlinear, combine the scientific assets of mechanical devices with the possibility of long distance controlled interactions enabled by traveling light. Here we demonstrate lightmediated frequency locking of three distant nanooptomechanical oscillators positioned in a cascaded configuration. The oscillators, integrated on a chip along a common coupling waveguide, are optically driven with a single laser and oscillate at gigahertz frequency. Despite an initial mechanical frequency disorder of hundreds of kilohertz, the guided light locks them all with a clear transition in the optical output. The experimental results are described by Langevin equations, paving the way to scalable cascaded optomechanical configurations.


Numerical modeling of the acoustic wave propagation across a homogenized rigid microstructure in the time domain Lombard, B., A. Maurel, and J. J. Marigo Journal of Computational Physics 335, 558577 (2017)
Résumé: © 2017 Elsevier Inc.Homogenization of a thin microstructure yields effective jump conditions that incorporate the geometrical features of the scatterers. These jump conditions apply across a thin but nonzero thickness interface whose interior is disregarded. This paper aims (i) to propose a numerical method able to handle the jump conditions in order to simulate the homogenized problem in the time domain, (ii) to inspect the validity of the homogenized problem when compared to the real one. For this purpose, we adapt the Explicit Simplified Interface Method originally developed for standard jump conditions across a zerothickness interface. Doing so allows us to handle arbitraryshaped interfaces on a Cartesian grid with the same efficiency and accuracy of the numerical scheme than those obtained in a homogeneous medium. Numerical experiments are performed to test the properties of the numerical method and to inspect the validity of the homogenization problem.
Motsclés: ADER scheme; Effective jump conditions; Homogenization; Immersed interface method; Timedomain wave propagation


Twoscale homogenization to determine effective parameters of thin metallicstructured films Marigo, J.J., and A. Maurel Proceedings Of The Royal Society AMathematical Physical And Engineering Sciences 472, no. 2192 (2016)
Motsclés: homogenization; thin film; matched asymptotic expansion; metamaterial


Critical investigation of calculation methods for the elastic velocities in anisotropic ice polycrystals Maurel, A., J. F. Mercier, and M. Montagnat Cryosphere 10, no. 6, 30633070 (2016)
Résumé: © Author(s) 2016.Crystallographic texture (or fabric) evolution with depth along ice cores can be evaluated using borehole sonic logging measurements. These measurements provide the velocities of elastic waves that depend on the ice polycrystal anisotropy, and they can further be related to the ice texture. To do so, elastic velocities need to be inverted from a modeling approach that relate elastic velocities to ice texture. So far, two different approaches can be found. A classical model is based on the effective medium theory; the velocities are derived from elastic wave propagation in a homogeneous medium characterized by an average elasticity tensor. Alternatively, a velocity averaging approach was used in the glaciology community that averages the velocities from a given population of single crystals with different orientations. In this paper, we show that the velocity averaging method is erroneous in the present context. This is demonstrated for the case of waves propagating along the clustering direction of a highly textured polycrystal, characterized by crystallographic c axes oriented along a single maximum (cluster). In this case, two different shear wave velocities are obtained while a unique velocity is theoretically expected. While making use of this velocity averaging method, reference work by Bennett (1968) does not end with such an unphysical result. We show that this is due to the use of erroneous expressions for the shear wave velocities in a single crystal, as the starting point of the averaging process. Because of the weak elastic anisotropy of ice single crystal, the inversion of the measured velocities requires accurate modeling approaches. We demonstrate here that the inversion method based on the effective medium theory provides physically based results and should therefore be favored.


Radiative transfer of acoustic waves in continuous complex media: Beyond the Helmholtz equation Baydoun, I., D. Baresch, R. Pierrat, and A. Derode Physical Review E 94, no. 5 (2016)


Multiple scattering of polarized light in disordered media exhibiting shortrange structural correlations Vynck, K., R. Pierrat, and R. Carminati Physical Review A 94, no. 3 (2016)


Homogenization models for thin rigid structured surfaces and films Marigo, J.J., and A. Maurel Journal Of The Acoustical Society Of America 140, no. 1, 260273 (2016)


Reshaping electromagnetic emissions with metasubstrate based on spoof plasmons Gao, Y., A. Maurel, and A. Ourir Progress In Electromagnetics Research C 65, 175182 (2016)
Résumé: © 2016, Electromagnetics Academy. All rights reserved.We investigate the efficiency of a metasurface supporting spoof plasmons to control the electromagnetic emission of a radiating element. The threedimensional metasurface is made of an array of metallic grounded rods, and it is used as the substrate of a printed antenna. Such a substrate provides a transmission band at low frequencies, corresponding to spoof plasmon propagation, and a total electromagnetic band gap above the cutoff frequency. We show how an efficient and directive emission with low sidelobe levels and backward radiation can be obtained when the operating frequency of the antenna is considered in the band gap. The role of the spoof plasmons is further demonstrated by tuning the transmission band at the operating frequency. The proposed metasubstrate is an original and efficient alternative to reshape the emission of electromagnetic sources.


Highdensity hyperuniform materials can be transparent Leseur, O., R. Pierrat, and R. Carminati Optica 3, no. 7, 763767 (2016)


One Single Static Measurement Predicts Wave Localization in Complex Structures Lefebvre, G., A. Gondel, M. Dubois, M. Atlan, F. Feppon, A. Labbe, C. Gillot, A. Garelli, M. Ernoult, S. Mayboroda, M. Filoche, and P. Sebbah Physical Review Letters 117, no. 7 (2016)


Improved multimodal method for the acoustic propagation in waveguides with a wall impedance and a uniform flow Mercier, J.F., and A. Maurel Proceedings Of The Royal Society AMathematical Physical And Engineering Sciences 472, no. 2190 (2016)
Motsclés: time harmonic; modal methods; acoustics in flows; multiple scattering


Nearfield to farfield characterization of speckle patterns generated by disordered nanomaterials Parigi, V., E. Perros, G. Binard, C. Bourdillon, A. Maitre, R. Carminati, V. Krachmalnicoff, and Y. De Wilde Optics Express 24, no. 7, 70197027 (2016)


Coherent Control of Photocurrent in a Strongly Scattering Photoelectrochemical System Liew, S. F., S. M. Popoff, S. W. Sheehan, A. Goetschy, C. A. Schmuttenmaer, A. D. Stone, and H. Cao Acs Photonics 3, no. 3, 449455 (2016)
Motsclés: photoelectrochemical; dyesensitized solar cells; wavefront shaping; multiple scattering; multimode interference


Quantum coherence of light emitted by two singlephoton sources in a structured environment CanaguierDurand, A., and R. Carminati Physical Review A  Atomic, Molecular, and Optical Physics 93, no. 3 (2016)
Résumé: © 2016 American Physical Society. We develop a theoretical framework for the analysis of the quantum coherence of light emitted by two independent singlephoton sources in an arbitrary environment. The theory provides design rules for the control of the degree of quantum coherence in terms of classical quantities widely used in nanophotonics. As an important example, we derive generalized conditions to generate superradiant and subradiant states of the emitters and demonstrate the ability of a structured environment to induce longrange quantum coherence. These results should have broad applications in quantum nanophotonics and for the sensing of fluorescent sources in complex environments.


LongRange PlasmonAssisted Energy Transfer between Fluorescent Emitters Bouchet, D., D. Cao, R. Carminati, Y. De Wilde, and V. Krachmalnicoff Physical Review Letters 116, no. 3 (2016)


Directional source of water waves by a crystal of surfacepiercing cylinders Chekroun, M., A. Maurel, V. Pagneux, and P. Petitjeans Comptes Rendus Mecanique 343, no. 12, 689699 (2015)
Motsclés: Metamaterial; Water waves; Periodic crystal


Effective birefringence to analyze sound transmission through a layer with subwavelength slits Maurel, A., S. Felix, J.F. Mercier, and A. Ourir Comptes Rendus Mecanique 343, no. 12, 612621 (2015)
Motsclés: Metamaterial; Spoof plasmon; Homogenization; Acoustic array


Thermal emission by a subwavelength aperture Joulain, K., Y. Ezzahri, and R. Carminati Journal of Quantitative Spectroscopy and Radiative Transfer 173, 16 (2016)
Résumé: © 2015 Elsevier Ltd. We calculate, by means of fluctuational electrodynamics, the thermal emission of an aperture separating from the outside, vacuum or a material at temperature T. We show that thermal emission is very different whether the aperture size is large or small compared to the thermal wavelength. Subwavelength apertures separating vacuum from the outside have their thermal emission strongly decreased compared to classical blackbodies which have an aperture much larger than the wavelength. A simple expression of their emissivity can be calculated and their total emissive power scales as T8 instead of T4 for large apertures. Thermal emission of disk of materials with a size comparable to the wavelength is also discussed. It is shown in particular that emissivity of such a disk is increased when the material can support surface waves such as phonon polaritons.
Motsclés: Fluctuational electrodynamics; Nanoscale Thermal emission; Phononpolaritons


Competition and Coexistence of Raman and Random Lasing in Silica/TitaniaBased Solid Foams Gaikwad, P., N. Bachelard, P. Sebbah, R. Backov, and R. A. L. Vallee Advanced Optical Materials 3, no. 11, 16401651 (2015)


Cooperative Emission of a Pulse Train in an Optically Thick Scattering Medium Kwong, C. C., T. Yang, D. Delande, R. Pierrat, and D. Wilkowski Physical Review Letters 115, no. 22 (2015)
Résumé: © 2015 American Physical Society. An optically thick cold atomic cloud emits a coherent flash of light in the forward direction when the phase of an incident probe field is abruptly changed. Because of cooperativity, the duration of this phenomena can be much shorter than the excited lifetime of a single atom. Repeating periodically the abrupt phase jump, we generate a train of pulses with short repetition time, high intensity contrast, and high efficiency. In this regime, the emission is fully governed by cooperativity even if the cloud is dilute.


Broadband Coherent Enhancement of Transmission and Absorption in Disordered Media Hsu, C. W., A. Goetschy, Y. Bromberg, A. D. Stone, and H. Cao Physical Review Letters 115, no. 22 (2015)
Résumé: © 2015 American Physical Society. Spatial modulation of the incident wave front has become a powerful method for controlling the diffusive transport of light in disordered media; however, such interferencebased control is intrinsically sensitive to frequency detuning. Here, we show analytically and numerically that certain wave fronts can exhibit strongly enhanced total transmission or absorption across bandwidths that are orders of magnitude broader than the spectral correlation width of the speckles. Such broadband enhancement is possible due to longrange correlations in coherent diffusion, which cause the spectral degrees of freedom to scale as the square root of the bandwidth rather than the bandwidth itself.


Empirical mode decomposition profilometry: smallscale capabilities and comparison to Fourier transform profilometry Lagubeau, G., P. Cobelli, T. Bobinski, A. Maurel, V. Pagneux, and P. Petitjeans Applied Optics 54, no. 32, 94099414 (2015)


Multiple scattering of elastic waves by pinned dislocation segments in a continuum Churochkin, D., F. Barra, F. Lund, A. Maurel, and V. Pagneux Wave Motion 60, 220230 (2016)
Résumé: © 2015 Elsevier B.V. The coherent propagation of elastic waves in a solid filled with a random distribution of pinned dislocation segments is studied to all orders in perturbation theory. It is shown that, within the independent scattering approximation, the perturbation series that generates the mass operator is a geometric series that can thus be formally summed. A divergent quantity is shown to be renormalizable to zero at low frequencies. At higher frequencies said quantity can be expressed in terms of a cutoff with dimensions of length, related to the dislocation length, and physical quantities can be computed in terms of two parameters, to be determined by experiment. The approach used in this problem is compared and contrasted with the scattering of de Broglie waves by deltafunction potentials as described by the Schrödinger equation.
Motsclés: Dislocations; Elastic waves; Multiple scattering; Renormalization


Scattering mean free path in continuous complex media: Beyond the Helmholtz equation Baydoun, I., D. Baresch, R. Pierrat, and A. Derode Physical Review E  Statistical, Nonlinear, and Soft Matter Physics 92, no. 3 (2015)
Résumé: © 2015 American Physical Society. We present theoretical calculations of the ensembleaveraged (or effective or coherent) wave field propagating in a heterogeneous medium considered as one realization of a random process. In the literature, it is usually assumed that heterogeneity can be accounted for by a random scalar function of the space coordinates, termed the potential. Physically, this amounts to replacing the constant wave speed in Helmholtz' equation by a spacedependent speed. In the case of acoustic waves, we show that this approach leads to incorrect results for the scattering mean free path, no matter how weak the fluctuations. The detailed calculation of the coherent wave field must take into account both a scalar and an operator part in the random potential. When both terms have identical amplitudes, the correct value for the scattering mean free paths is shown to be more than 4 times smaller (13/3, precisely) in the lowfrequency limit, whatever the shape of the correlation function. Based on the diagrammatic approach of multiple scattering, theoretical results are obtained for the selfenergy and mean free path within Bourret's and onshell approximations. They are confirmed by numerical experiments.


Intensity correlations between reflected and transmitted speckle patterns Fayard, N., A. Cazé, R. Pierrat, and R. Carminati Physical Review A  Atomic, Molecular, and Optical Physics 92, no. 3 (2015)
Résumé: © 2015 American Physical Society. ©2015 American Physical Society. We study theoretically the spatial correlations between the intensities measured at the input and output planes of a disordered scattering medium. We show that at large optical thicknesses, a longrange spatial correlation persists and takes negative values. For small optical thicknesses, shortrange and longrange correlations coexist, with relative weights that depend on the optical thickness. These results may have direct implications for the control of wave transmission through complex media by wavefront shaping, thus finding applications in sensing, imaging, and information transfer.


Tuning the wavelength of spoof plasmons by adjusting the impedance contrast in an array of penetrable inclusions Cordero, M. L., A. Maurel, J. F. Mercier, S. Félix, and F. Barra Applied Physics Letters 107, no. 8 (2015)
Résumé: © 2015 AIP Publishing LLC. While spoof plasmons have been proposed in periodic arrays of soundhard inclusions, we show that they also exist when inclusions are penetrable. Moreover, we show that their wavelength can be tuned by the impedance mismatch between the inclusion material and the surrounding medium, beyond the usual effect of filling fraction in the array. It is demonstrated that soundsoft materials increase the efficiency in the generation of subwavelength plasmons, with much lower wavelengths than soundhard materials and than a homogeneous slab. An application to the generation of acoustic spoof plasmons by an ultra compact array of air/polydimethylsiloxane inclusions in water is proposed with plasmon wavelength tunable up to deep subwavelength scales.


The Use of Ultrasound to Measure Dislocation Density Barra, F., R. EspinozaGonzalez, H. Fernandez, F. Lund, A. Maurel, and V. Pagneux Jom 67, no. 8, 18561863 (2015)


Experimental demonstration of epsilonnearzero water waves focusing Bobinski, T., A. Eddi, P. Petitjeans, A. Maurel, and V. Pagneux Applied Physics Letters 107, no. 1 (2015)
Résumé: © 2015 AIP Publishing LLC. We explore an εnearzero analogue for water waves using deep water and shallow water domains to obtain different phase velocities. Being inherently non linear, water waves permit to inspect focusing of harmonically generated waves. Experimental measurements show cascade of focal spots up to the fourth harmonic, allowing sub wavelength focusing with respect to the first harmonic wavelength.


Subwavelength focusing in bubbly media using broadband time reversal Lanoy, M., R. Pierrat, F. Lemoult, M. Fink, V. Leroy, and A. Tourin Physical Review B 91, no. 22 (2015)


Modal method for the 2D wave propagation in heterogeneous anisotropic media Maurel, A., J.F. Mercier, and S. Felix Journal Of The Optical Society Of America AOptics Image Science And Vision 32, no. 5, 979990 (2015)


Breakthroughs in photonics 2014: Random lasers Sebbah, P., and R. Carminati IEEE Photonics Journal 7, no. 3 (2015)
Résumé: © 2015 IEEE. Multiple scattering of light in a disordered medium with gain may provide for the necessary feedback to achieve lasing action without an optical cavity. In addition to the fundamental interest raised by this regime of lightmatter interaction in open cavity, the relatively simple design of these socalled "random lasers" and the possibility to control their emission open perspective of new applications in domains not yet covered by conventional lasers.
Motsclés: Laser; random media


Propagation of elastic waves through textured polycrystals: application to ice Maurel, A., F. Lund, and M. Montagnat Proceedings Of The Royal Society AMathematical Physical And Engineering Sciences 471, no. 2177 (2015)
Motsclés: effective medium; elastic wave propagation; polycrystal; ice


Linear and nonlinear Rabi oscillations of a twolevel system resonantly coupled to an Andersonlocalized mode Bachelard, N., R. Carminati, P. Sebbah, and C. Vanneste Physical Review A 91, no. 4 (2015)


Wave propagation in a waveguide containing restrictions with circular arc shape Félix, S., A. Maurel, and J. F. Mercier Journal of the Acoustical Society of America 137, no. 3, 12741281 (2015)
Résumé: © 2015 Acoustical Society of America. A multimodal method is used to analyze the wave propagation in waveguides containing restrictions (or corrugations) with circular arc shapes. This is done using a geometrical transformation which transforms the waveguide with complex geometry in the real space to a straight waveguide in the transformed space, or virtual space. In this virtual space, the Helmholtz equation has a modified structure which encapsulates the complexity of the geometry. It is solved using an improved modal method, which was proposed in a paper by A. Maurel, J.F. Mercier, and S. Félix [Proc. R. Soc. A 470, 20130743 (2014)], that increases the accuracy and convergence of usual multimodal formulations. Results show the possibility to solve the wave propagation in a waveguide with a high density of circular arc shaped scatterers.


Disorder persistent transparency within the bandgap of a periodic array of acoustic Helmholtz resonators Richoux, O., A. Maurel, and V. Pagneux Journal of Applied Physics 117, no. 10 (2015)
Résumé: © 2015 AIP Publishing LLC. In this paper, the influence of disorder on 1D periodic lattice of resonant scatterers is inspected. These latter have multiple resonance frequencies which produce band gaps in the transmission spectrum. One peculiarity of the presented system is that it is chosen with a nearly perfect overlap between the Bragg and the second hybridization band gaps. In the case of a perfectly ordered lattice, and around this overlap, this produces a narrow transparency band within a large second bandgap. As expected, the effect of the disorder is generally to increase the width of the band gaps. Nevertheless, the transparency band appears to be robust with respect to an increase in the disorder. In this paper, we study this effect by means of experimental investigations and numerical simulations.


Mapping the radiative and the apparent nonradiative local density of states in the near field of a metallic nanoantenna Cao, D., A. Cazé, M. Calabrese, R. Pierrat, N. Bardou, S. Collin, R. Carminati, V. Krachmalnicoff, and Y. De Wilde ACS Photonics 2, no. 2, 189193 (2015)
Résumé: © 2015 American Chemical Society. We present a novel method to extract the various contributions to the photonic local density of states from nearfield fluorescence maps. The approach is based on the simultaneous mapping of the fluorescence intensity and decay rate and on the rigorous application of the reciprocity theorem. It allows us to separate the contributions of the radiative and the apparent nonradiative local density of states to the change in the decay rate. The apparent nonradiative contribution accounts for losses due to radiation out of the detection solid angle and to absorption in the environment. Data analysis relies on a new analytical calculation, and does not require the use of numerical simulations. One of the most relevant applications of the method is the characterization of nanostructures aimed at maximizing the number of photons emitted in the detection solid angle, which is a crucial issue in modern nanophotonics.
Motsclés: fluorescence microscopy; local density of states; nearfield scanning probe; plasmonic nanoantennas; radiative decay rate; reciprocity theorem


Electromagnetic field correlations in threedimensional speckles Dogariu, A. C., and R. Carminati Physics Reports 559, 129 (2015)
Résumé: © 2015. We describe recent developments in the characterization of threedimensional speckle fields produced by scattering of electromagnetic waves. In many practical situations the description of such fields requires approaches going beyond the Gaussian statistics approximation. Quantitative measures of spatial coherence and polarization can be defined from the fieldfield correlation matrix, known as the crossspectral density matrix in coherence theory. The complex degree of mutual polarization provides a measure of the similarity between polarization states at two different points. The degree of spatial coherence describes spatial coherence and averages out the polarization properties. We discuss their behavior in speckle fields produced by multiple scattering in disordered materials. A number of nonuniversal properties arise, that are related to the internal microscopic structure of the scattering medium. Nonuniversality affects observables quantities, such as spatial correlations in speckle patterns measured in the near field of the medium surface, statistics of the local density of states or the depolarization of the exciting electromagnetic field due to scattering. Specific microscopic scales are necessary to describe the nonuniversal behaviors, that characterize the scaledependent morphology of the scattering medium.
Motsclés: Coherence; Polarization; Random fields; Speckle


Experiments on Maxwell's fisheye dynamics in elastic plates Lefebvre, G., M. Dubois, R. Beauvais, Y. Achaoui, R. K. Ing, S. Guenneau, and P. Sebbah Applied Physics Letters 106, no. 2 (2015)


Improved multimodal methods for the acoustic propagation in waveguides with finite wall impedance Félix, S., A. Maurel, and J. F. Mercier Wave Motion 54, 110 (2015)
Résumé: © 2014 Elsevier B.V. We address the problem of acoustic propagation in waveguides with wall impedance, or Robin, boundary condition. Two improved multimodal methods are developed to remedy the problem of the low convergence of the series in the standard modal approach. In the first improved method, the series is enriched with an additional mode, which is thought to be able to restore the right boundary condition. The second improved method consists in a reformulation of the expansions able to restore the right boundary conditions for any truncation, similar to polynomial subtraction technique. Surprisingly, the first improved method is found to be the most efficient. Notably, the convergence of the scattering properties is increased from N1 in the standard modal method to N3 in the reformulation and N5 in the formulation with a supplementary mode. The improved methods are shown to be of particular interest when surface waves are generated near the impedance wall.
Motsclés: Boundary modes; Modal method; Robin condition; Waveguides


Speckle fluctuations resolve the interdistance between incoherent point sources in complex media Carminati, R., G. A. Cwilich, L. S. FroufePérez, and J. J. Sáenz Physical Review A  Atomic, Molecular, and Optical Physics 91, no. 2 (2015)
Résumé: © 2015 American Physical Society. We study the fluctuations of the light emitted by two identical incoherent point sources in a disordered environment. The intensityintensity correlation function and the speckle contrast, obtained after proper temporal and configurational averaging, encode the relative distance between the two sources. This suggests the intriguing possibility that intensity measurements at only one point in a speckle pattern produced by two incoherent sources can provide information about the relative distance between the sources, with a precision that is not limited by diffraction. The theory also suggests an alternative approach to the Green'sfunction retrieval technique, where the correlations of the isotropic ambient noise detected by two receivers are replaced by a measurement at a single point of the noise due to two fluctuating incoherent sources.


Probing twodimensional Anderson localization without statistics Leseur, O., R. Pierrat, J. J. Sáenz, and R. Carminati Physical Review A  Atomic, Molecular, and Optical Physics 90, no. 5 (2014)
Résumé: © 2014 American Physical Society. We investigate the possibility of using the independence of the transmitted speckle pattern on the illumination condition as a signature of Anderson localization in a single configuration of a twodimensional and open disordered medium. The analysis is based on exact numerical simulations of multiple light scattering. We introduce a similarity function that we propose as a reliable observable to probe Anderson localization without requiring any statistical averaging over an ensemble.


Cooperative emission of a coherent superflash of light Kwong, C. C., T. Yang, M. S. Pramod, K. Pandey, D. Delande, R. Pierrat, and D. Wilkowski Physical Review Letters 113, no. 22 (2014)
Résumé: © 2014 American Physical Society. We investigate the transient coherent transmission of light through an optically thick cold strontium gas. We observe a coherent superflash just after an abrupt probe extinction, with peak intensity more than three times the incident one. We show that this coherent superflash is a direct signature of the cooperative forward emission of the atoms. By engineering fast transient phenomena on the incident field, we give a clear and simple picture of the physical mechanisms at play.


Invariance property of wave scattering through disordered media Pierrat, R., P. Ambichl, S. Gigan, A. Haber, R. Carminati, and S. Rotter Proceedings of the National Academy of Sciences of the United States of America 111, no. 50, 1776517770 (2014)
Résumé: A fundamental insight in the theory of diffusive random walks is that the mean length of trajectories traversing a finite open system is independent of the details of the diffusion process. Instead, the mean trajectory length depends only on the system's boundary geometry and is thus unaffected by the value of the mean free path. Here we show that this result is rooted on a much deeper level than that of a random walk, which allows us to extend the reach of this universal invariance property beyond the diffusion approximation. Specifically, we demonstrate that an equivalent invariance relation also holds for the scattering of waves in resonant structures as well as in ballistic, chaotic or in Anderson localized systems. Our work unifies a number of specific observations made in quite diverse fields of science ranging from the movement of ants to nuclear scattering theory. Potential experimental realizations using light fields in disordered media are discussed.
Motsclés: Diffusion; Disordered media; Random walk; Time delay; Wave scattering


Electromagnetic density of states in complex plasmonic systems Carminati, R., A. Cazé, D. Cao, F. Peragut, V. Krachmalnicoff, R. Pierrat, and Y. De Wilde Surface Science Reports 70, no. 1, 141 (2015)
Résumé: © 2014 Elsevier B.V. All rights reserved. Nanostructured materials offer the possibility to tailor lightmatter interaction at scales below the wavelength. Metallic nanostructures benefit from the excitation of surface plasmons that permit light concentration at ultrasmall length scales and ultrafast time scales. The local density of states (LDOS) is a central concept that drives basic processes of lightmatter interaction such as spontaneous emission, thermal emission and absorption. We introduce theoretically the concept of LDOS, emphasizing the specificities of plasmonics. We connect the LDOS to real observables in nanophotonics, and show how the concept can be generalized to account for spatial coherence. We describe recent methods developed to probe or map the LDOS in complex nanostructures ranging from nanoantennas to disordered metal surfaces, based on dynamic fluorescence measurements or on the detection of thermal radiation.
Motsclés: Cross density of states; Local density of states; Plasmonics; Spatial coherence; Spontaneous emission; Thermal radiation


Timedriven superoscillations with negative refraction Dubois, M. A., E. Bossy, S. Enoch, S. Guenneau, G. Lerosey, and P. Sebbah Physical Review Letters 114, no. 1 (2015)
Résumé: © 2015 American Physical Society. The flatlens concept based on negative refraction proposed by Veselago in 1968 has been mostly investigated in the monochromatic regime. It was recently recognized that time development of the superlensing effect discovered in 2000 by Pendry is yet to be assessed and may spring surprises: Timedependent illumination could improve the spatial resolution of the focusing. We investigate dynamics of flexural wave focusing by a 45°tilted square lattice of circular holes drilled in a duralumin plate. Timeresolved experiments reveal that the focused image shrinks with time below the diffraction limit, with a lateral resolution increasing from 0.8λ to 0.35λ, whereas focusing under harmonic excitation remains diffraction limited. Modal analysis reveals the role in pulse reconstruction of radiating lens resonances, which repeatedly selfsynchronize at the focal spot to shape a superoscillating field.


Local control of the excitation of surface plasmon polaritons by nearfield magnetooptical Kerr effect Vincent, R., H. Marinchio, J. J. Saenz, and R. Carminati Physical Review B 90, no. 24 (2014)


Generalized method for retrieving effective parameters of anisotropic metamaterials Castanie, A., J.F. Mercier, S. Felix, and A. Maurel Optics Express 22, no. 24, 2993729953 (2014)


Signatures of Levy flights with annealed disorder Baudouin, Q., R. Pierrat, A. Eloy, E. J. NunesPereira, P.A. Cuniasse, N. Mercadier, and R. Kaiser Physical Review E 90, no. 5 (2014)


Disorder as a Playground for the Coexistence of Optical Nonlinear Effects: Competition between Random Lasing and Stimulated Raman Scattering in Complex Porous Materials Bachelard, N., P. Gaikwad, R. Backov, P. Sebbah, and R. A. L. Vallee Acs Photonics 1, no. 11, 12061211 (2014)
Motsclés: random lasers; Raman lasers; nonlinear effects; porous materials


Local transformation leading to an efficient Fourier modal method for perfectly conducting gratings Felix, S., A. Maurel, and J.F. Mercier Journal Of The Optical Society Of America AOptics Image Science And Vision 31, no. 10, 22492255 (2014)


Mapping and Quantifying Electric and Magnetic Dipole Luminescence at the Nanoscale Aigouy, L., A. Caze, P. Gredin, M. Mortier, and R. Carminati Physical Review Letters 113, no. 7 (2014)


Adaptive pumping for spectral control of random lasers Bachelard, N., S. Gigan, X. Noblin, and P. Sebbah Nature Physics 10, no. 6, 426431 (2014)


Extraordinary transmission through subwavelength dielectric gratings in the microwave range Akarid, A., A. Ourir, A. Maurel, S. Felix, and J.F. Mercier Optics Letters 39, no. 13, 37523755 (2014)


Analysis of coherence properties of partially polarized light in 3D and application to disordered media Refregier, P., V. Wasik, K. Vynck, and R. Carminati Optics Letters 39, no. 8, 23622365 (2014)


Partially Pumped Random Lasers Andreasen, J., N. Bachelard, S. B. N. Bhaktha, H. Cao, P. Sebbah, and C. Vanneste International Journal Of Modern Physics B 28, no. 5 (2014)
Motsclés: Random lasers; laser pumping; multiple scattering


Wood's anomalies for arrays of dielectric scatterers Maurel, A., S. Felix, J.F. Mercier, A. Ourir, and Z. E. Djeffal 9 (2014)
Résumé: The Rayleigh Wood anomalies refer to an unexpected repartition of the electromagnetic energy between the several interference orders of the light emerging from a grating. Since Hessel and Oliner (Appl. Opt. 4, 12751297 (1965)), several studies have been dedicated to this problem, focusing mainly on the case of metallic gratings. In this paper, we derive explicit expressions of the reflection coefficients in the case of dielectric gratings using a perturbative approach. This is done in a multimodal description of the field combined with the use of the admittance matrix, analog to the socalled electromagnetic impedance. Comparisons with direct numerical calculations show a good agreement with our analytical prediction.


Magnetooptical Kerr effect in resonant subwavelength nanowire gratings Marinchio, H., R. Carminati, A. GarcíaMartín, and J. J. Sáenz New Journal of Physics 16, no. 1, 015007015007 (2014)
Résumé: Periodic arrays of nanorods can present a resonant response at specific geometric conditions. We use a multiple scattering approach to analyze the optical response of subwavelength nanowire gratings made of arbitrary anisotropic materials. When the rods are made of magnetooptical dielectrics we show that there is a complex interplay between the geometric resonances of the grating and the magnetooptical Kerr effects (MOKE) response. As we will show, for a given polarization of the incident light, a resonant magnetooptical response can be obtained by tuning the incidence angle and grating parameters to operate near the resonance condition for the opposite polarization. Our results could be important to understand and optimize MOKE structures and devices based on resonant subwavelength gratings and could open new perspectives in sensing applications.


Wave propagation through penetrable scatterers in a waveguide and through a penetrable grating Maurel, A., J.F. Mercier, and S. Félix The Journal of the Acoustical Society of America 135, 165174 (2014)
Résumé: A multimodal method based on the admittance matrix is used to analyze wave propagation through scatterers of arbitrary shape. Two cases are considered: a waveguide containing scatterers, and the scattering of a plane wave at oblique incidence to an infinite periodic row of scatterers. In both cases, the problem reduces to a system of two sets of firstorder differential equations for the modal components of the wavefield, similar to the system obtained in the rigorous coupled wave analysis. The system can be solved numerically using the admittance matrix, which leads to a stable numerical method, the basic properties of which are discussed (convergence, reciprocity, energy conservation). Alternatively, the admittance matrix can be used to get analytical results in the weak scattering approximation. This is done using the plane wave approximation, leading to a generalized version of the Webster equation and using a perturbative method to analyze the Wood anomalies and Fano resonances.


Polarization and spatial coherence of electromagnetic waves in uncorrelated disordered media Vynck, K., R. Pierrat, and R. Carminati Physical Review A 89, no. 1, 013842 (2014)
Résumé: Spatial field correlation functions represent a key quantity for the description of mesoscopic phenomena in disordered media and the optical characterization of complex materials. Yet many aspects related to the vector nature of light waves have not been investigated so far. We study theoretically the polarization and coherence properties of electromagnetic waves produced by a dipole source in a threedimensional uncorrelated disordered medium. The spatial field correlation matrix is calculated analytically using a multiplescattering theory for polarized light. This allows us to provide a formal description of the light depolarization process in terms of “polarization eigenchannels” and to derive analytical formulas for the spatial coherence of multiply scattered light.


Experimental realization of a waterwave metamaterial shifter Berraquero, C. P., A. Maurel, P. Petitjeans, and V. Pagneux Physical Review E  Statistical, Nonlinear, and Soft Matter Physics 88, no. 5 (2013)
Résumé: We demonstrate by quantitative experimental measurements that metamaterials with anisotropic properties can be used in the context of water waves to produce a reflectionless bent waveguide. The anisotropic medium consists in a bathymetry with subwavelength layered structure that shifts the wave in the direction of the waveguide bending (10, 20, and 30 ). The waveguide filled with such metamaterial is tested experimentally and compared to a reference empty bent waveguide. The experimental method used to characterize the wave field allows for spacetime resolved measurements of water elevation. Results show the efficiency of the shifter. Modal treatment of the experimental data confirms that the metamaterial prevents higher modes from being excited in the waveguide. © 2013 American Physical Society.


Flat lens for pulse focusing of elastic waves in thin plates Dubois, M., M. Farhat, E. Bossy, S. Enoch, S. Guenneau, and P. Sebbah Applied Physics Letters 103, no. 7, 071915 (2013)
Résumé: The ability of lefthanded materials to overcome the diffraction limit was first considered as one of the most exciting and challenging outcomes of the negative refraction concept. Flat lens focusing of elastic waves is, however, a challenge. We demonstrate broadband focusing of elastic waves at 10 kHz carrier frequency, below the first stop band, in a 45°tilted square array of circular air holes perforated in a Duraluminium thin plate. By adjusting the relative thickness of the outer plate we achieve largeangle negative refraction with diffractionlimited lateral resolution. We find good agreement with a simple beamlattice model and finitedifference timedomain simulations. © 2013 AIP Publishing LLC.
Motsclés: Circular airholes; Diffraction limited; Diffraction limits; Finite difference time domain simulations; Lateral resolution; Left handed materials; Negative refractions; Relative thickness; Diffraction; Focusing; Light refraction; Refraction; Elastic waves


Underwater depth reconstruction by local water wave measurements Przadka, A., P. Petitjeans, V. Pagneux, A. Maurel, and R. K. Ing Applied Physics Letters 103, no. 14 (2013)
Résumé: We present an experimental study of underwater depth reconstruction obtained by a method based on the Bessel series expansion of the solutions of the 2D linear water wave equation. This is achieved by measuring capillarygravity waves using a contactless spacetime resolved Fourier Transform Profilometry method. The ability of the method is exemplified for several type of bathymetry in laboratory experiments. © 2013 AIP Publishing LLC.


Surface plasmons: A probe for graphene electronics Carminati, R. Nature Nanotechnology (2013)


Enhanced transmission through gratings: Structural and geometrical effects Maurel, A., S. Félix, and J.F. Mercier Physical Review B  Condensed Matter and Materials Physics 88, no. 11 (2013)
Résumé: Homogenization theory is used to derive the effective properties of gratings with complex subwavelength structures. Going beyond the effect of the filling fraction, geometrical effects are analyzed using a twostep homogenization process. An explicit expression for the transmission spectrum is derived, able to predict the FabryPerot resonances and the Brewster angle realizing broadband extraordinary transmission. With the same filling fraction, one expects from this analytical expression that gratings with different geometries may display very different transmission properties. This sensitivity to the microstructure geometry is exemplified in the case of gratings made of hard material and made of dielectric material. The analytical results are shown to be within a few percentage points as compared to fullwave numerical simulations, paving the way for transmission properties tuned by structural and geometrical manipulations. © 2013 American Physical Society.


Strong coupling to twodimensional Anderson localized modes Cazé, A., R. Pierrat, and R. Carminati Physical Review Letters 111, no. 5 (2013)
Résumé: We use a scattering formalism to derive a condition of strong coupling between a resonant scatterer and an Anderson localized mode for electromagnetic waves in two dimensions. The strong coupling regime is demonstrated based on exact numerical simulations, in perfect agreement with theory. The strong coupling threshold can be expressed in terms of the Thouless conductance and the Purcell factor. This connects key concepts in transport theory and cavity quantum electrodynamics, and provides a practical tool for the design or analysis of experiments. © 2013 American Physical Society.


Acoustic propagation in nonuniform waveguides: Revisiting Webster equation using evanescent boundary modes Mercier, J.F., and A. Maurel Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 469, no. 2156 (2013)
Résumé: The scattering of an acoustic wave propagating in a nonuniform waveguide is inspected by revisiting improved multimodal methods in which the introduction of additional modes, socalled boundary modes, allows to better satisfy the Neumann boundary conditions at the varying walls. In this paper, we show that the additional modes can be identified as evanescent modes. Although nonphysical, these modes are able to tackle the evanescent part of the field omitted by the truncation and are able to restore the right boundary condition at the walls. In the lowfrequency regime, the system can be solved analytically, and the solution for an incident plane wave including one or two boundary modes is shown to be an improvement of the usual Webster equation. © 2013 The Author(s) Published by the Royal Society. All rights reserved.
Motsclés: Boundary modes; Modal method; Nonuniform waveguide; Scalar waves; Webster equation; Boundary modes; Modal method; Nonuniform; Scalar waves; Webster equation; Boundary conditions; Waveguides


Tunneling of electromagnetic energy in multiple connected leads using ∈nearzero materials Ourir, A., A. Maurel, and V. Pagneux Optics Letters 38, no. 12, 20922094 (2013)
Résumé: A realization of a reflectionless power splitter is proposed by use of a metamaterial junction. To design the junction, the electromagnetic wave transmission in multiple connected leads is investigated theoretically and numerically. A closed analytical form is derived for the scattering matrix of any geometry of the interconnected leads. We show that the use of a junction made of ∈nearzero (ENZ) material allows production of perfect transmission. This can be achieved by reducing the area of the ENZ junction (squeezing effect) and by tuning the widths of the output leads with respect to the input lead. It is also shown that the same effect is obtained without squeezed junction by using a match impedance zero index material (MIZIM junction). © 2013 Optical Society of America.
Motsclés: Analytical forms; Power splitters; Production of; Reflectionless; Scattering matrices; Squeezing effect; Zeroindex materials; Metamaterials; Scattering parameters; Electromagnetic waves


Towards a full characterization of a plasmonic nanostructure with a fluorescent nearfield probe Krachmalnicoff, V., D. Cao, A. Cazé, E. Castanié, R. Pierrat, N. Bardou, S. Collin, R. Carminati, and Y. De Wilde Optics Express 21, no. 9, 1153611545 (2013)
Résumé: We report on the experimental and theoretical study of the spatial fluctuations of the local density of states (EMLDOS) and of the fluorescence intensity in the nearfield of a gold nanoantenna. EMLDOS, fluorescence intensity and topography maps are acquired simultaneously by scanning a fluorescent nanosource grafted on the tip of an atomic force microscope at the surface of the sample. The results are in good quantitative agreement with numerical simulations. This work paves the way for a full nearfield characterization of an optical nanoantenna. © 2013 Optical Society of America.
Motsclés: Atomic force microscope (AFM); Fluorescence intensities; Local density of state; Nearfield characterizations; Optical nano antennas; Plasmonic nanostructures; Quantitative agreement; Spatial fluctuation; Atomic force microscopy; Nanostructures; Surface topography; Fluorescence


Subwavelength focusing inside an open disordered medium by time reversal at a single point antenna Pierrat, R., C. Vandenbem, M. Fink, and R. Carminati Physical Review A  Atomic, Molecular, and Optical Physics 87, no. 4 (2013)
Résumé: We study theoretically light focusing at subwavelength scale inside a disordered strongly scattering open medium. We show that broadband time reversal at a single point antenna, in conjunction with nearfield interactions and multiple scattering, produces spatial focusing with a quality comparable to that obtained in an ideal closed cavity. This provides different perspectives for superresolved optical imaging and coherent control of single nanosources or absorbers in complex media. © 2013 American Physical Society.
Motsclés: Closed cavity; Coherent control; Disordered medium; Near field interactions; Optical imaging; Spatial focusing; Subwavelength focusing; Subwavelength scale; Antennas; Focusing


Spatial coherence in complex photonic and plasmonic systems Cazé, A., R. Pierrat, and R. Carminati Physical Review Letters 110, no. 6 (2013)
Résumé: The concept of cross density of states characterizes the intrinsic spatial coherence of complex photonic or plasmonic systems, independently of the illumination conditions. Using this tool and the associated intrinsic coherence length, we demonstrate unambiguously the spatial squeezing of eigenmodes on disordered fractal metallic films, thus clarifying a basic issue in plasmonics. © 2013 American Physical Society.
Motsclés: Coherence lengths; Density of state; Eigen modes; Illumination conditions; Plasmonic; Plasmonics; Spatial coherence; Atomic physics; Physics; Plasmons


Recovering fluorophore location and orientation from lifetimes Irishina, N., M. Moscoso, and R. Carminati Optics Express 21, no. 1, 421430 (2013)
Résumé: In this paper, we study the possibility of using lifetime data to estimate the position and orientation of a fluorescent dipole source within a disordered medium. The vector FoldyLax equations are employed to calculate the interaction between the fluorescent source and the scatterers that are modeled as pointscatterers. The numerical experiments demonstrate that if good prior knowledge about the positions of the scatterers is available, the position and orientation of the dipole source can be retrieved from its lifetime data with precision. If there is uncertainty about the positions of the scatterers, the dipole source position can be estimated within the same level of uncertainty. © 2013 Optical Society of America.
Motsclés: Dipole sources; Disordered medium; Lifetime data; Numerical experiments; Prior knowledge; Fluorescence; Uncertainty analysis; Scattering


Spreading dynamics of drop impacts Lagubeau, G., M. A. Fontelos, C. Josserand, A. Maurel, V. Pagneux, and P. Petitjeans Journal of Fluid Mechanics 713, 5060 (2012)
Résumé: We present an experimental study of drop impact on a solid surface in the spreading regime with no splashing. Using the spacetimeresolved Fourier transform profilometry technique, we can follow the evolution of the drop shape during the impact. We show that a selfsimilar dynamical regime drives the drop spreading until the growth of a viscous boundary layer from the substrate selects a residual minimal film thickness. Finally, we discuss the interplay between capillary and viscous effects in the spreading dynamics, which suggests a pertinent impact parameter. © 2012 Cambridge University Press.
Motsclés: drops; drops and bubbles; interfacial flows (free surface); Drop Impact; Drop shape; Drop spreading; Drops and bubbles; Dynamical regime; Experimental studies; Fourier transform profilometry; Free surfaces; Impactparameter; Selfsimilar; Solid surface; Spreading dynamics; Viscous boundary layers; Viscous effect; Dynamics; Film growth; Drops; bubble; capillary pressure; droplet; fluid dynamics; free surface flow; viscosity


Optofluidic random laser Shivakiran Bhaktha, B. N., N. Bachelard, X. Noblin, and P. Sebbah Applied Physics Letters 101, no. 15 (2012)
Résumé: Random lasing is reported in a dyecirculated structured polymeric microfluidic channel. The role of disorder, which results from limited accuracy of photolithographic process, is demonstrated by the variation of the emission spectrum with localpump position and by the extreme sensitivity to a local perturbation of the structure. Thresholds comparable to those of conventional microfluidic lasers are achieved, without the hurdle of stateoftheart cavity fabrication. Potential applications of optofluidic random lasers for onchip sensors are discussed. Introduction of random lasers in the field of optofluidics is a promising alternative to onchip laser integration with light and fluidic functionalities. © 2012 American Institute of Physics.
Motsclés: Emission spectrums; Local perturbation; Microfluidic channel; Microfluidic lasers; On chips; Onchip sensors; Optofluidics; Photolithographic process; Potential applications; Random lasers; Random lasing; Emission spectroscopy; Photolithography; Sensitivity analysis; Laser beams


Radiative and nonradiative local density of states on disordered plasmonic films Cazé, A., R. Pierrat, and R. Carminati Photonics and Nanostructures  Fundamentals and Applications 10, no. 4, 339344 (2012)
Résumé: We present numerical calculations of the local density of optical states (LDOS) in the near field of disordered plasmonic films. The calculations are based on an integral volume method, that takes into account polarization and retardation effects, and allows us to discriminate radiative and nonradiative contributions to the LDOS. At short distance, the LDOS fluctuations are dominated by nonradiative channels, showing that changes in the spontaneous dynamics of dipole emitters are driven by nonradiative coupling to plasmon modes. Maps of radiative and nonradiative LDOS exhibit strong fluctuations, but with substantially different spatial distributions. © 2012 Elsevier B.V. All rights reserved.
Motsclés: Disordered systems; Fractals; Local density of states; Metallic films; Numerical simulations; Plasmons; Disordered system; Local density; Local density of state; Near fields; Nonradiative; Nonradiative channels; Numerical calculation; Optical state; Plasmon modes; Plasmonic; Retardation effect; Volume method; Computer simulation; Electrical engineering; Fractals; Hardware; Metallic films; Plasmons


Time reversal of water waves Przadka, A., S. Feat, P. Petitjeans, V. Pagneux, A. Maurel, and M. Fink Physical Review Letters 109, no. 6 (2012)
Résumé: We present time reversal experiments demonstrating refocusing of gravitycapillary waves in a water tank cavity. Owing to the reverberating effect of the cavity, only a few channels are sufficient to reconstruct the surface wave at the point source, even if the absorption is not negligible. Spacetimeresolved measurements of the waves during the refocusing allow us to quantitatively demonstrate that the quality of the refocusing increases linearly with the number of reemitting channels. Numerical simulations corresponding to water waves at larger scales, with negligible damping, indicate the possibility of very high quality refocusing. © 2012 American Physical Society.
Motsclés: Gravity capillary waves; High quality; Point sources; Reemitting; Time reversal; Surface waves; Water tanks; Water waves


Erratum: Propagation of guided waves through weak penetrable scatterers (Journal of the Acoustical Society of America (2012) 131:3 (18741889)) Maurel, A., and J.F. Mercier Journal of the Acoustical Society of America 132, no. 2, 1230 (2012)


Taming random lasers through active spatial control of the pump Bachelard, N., J. Andreasen, S. Gigan, and P. Sebbah Physical Review Letters 109, no. 3 (2012)
Résumé: Active control of the spatial pump profile is proposed to exercise control over random laser emission. We demonstrate numerically the selection of any desired lasing mode from the emission spectrum. An iterative optimization method is employed, first in the regime of strong scattering where modes are spatially localized and can be easily selected using local pumping. Remarkably, this method works efficiently even in the weakly scattering regime, where strong spatial overlap of the modes precludes spatial selectivity. A complex optimized pump profile is found, which selects the desired lasing mode at the expense of others, thus demonstrating the potential of pump shaping for robust and controllable single mode operation of a random laser. © 2012 American Physical Society.
Motsclés: Active control; Emission spectrums; Exercise control; Iterative Optimization; Lasing modes; Local pumping; Random laser emission; Random lasers; Scattering regime; Single mode operation; Spatial control; Spatial overlap; Spatial selectivity; Emission spectroscopy; Laser beams; Pumps


Distance dependence of the local density of states in the near field of a disordered plasmonic film Castanié, E., V. Krachmalnicoff, A. Cazé, R. Pierrat, Y. De Wilde, and R. Carminati Optics Letters 37, no. 14, 30063008 (2012)
Résumé: We measure the statistical distribution of the photonic local density of states in the near field of a semicontinuous gold film. By varying the distance between the measurement plane and the film, we show that nearfield confined modes play a major role in the width of the distribution. Numerical simulations in good agreement with experiments allow us to point out the influence of nonradiative decay channels at short distance. © 2012 Optical Society of America.
Motsclés: Confined modes; Gold film; Local density of state; Measurement planes; Near fields; Nearfield; Nonradiative decay channels; Plasmonic; Semicontinuous; Statistical distribution; Optics; Optoelectronic devices


Light scattering by a magnetooptical nanoparticle in front of a flat surface: Perturbative approach Marinchio, H., J. J. Sáenz, and R. Carminati Physical Review B  Condensed Matter and Materials Physics 85, no. 24 (2012)
Résumé: We develop a perturbative formalism for the interaction of a magnetooptical nanoparticle with a flat surface made of a dielectric or metallic material. The formalism leads to a simple interpretation of the interplay between the purely dielectric and the magnetooptical responses, in terms of excitation of (and radiation by) two orthogonal electric dipoles. We analyze two different routes for the enhancement of the magnetooptical response with respect to the purely dielectric contribution, both based on the nanoparticlesurface interaction. The enhancement is discussed in terms of relevant magnetooptical signals, such as changes in reflectivity, polarization (Kerr) rotation, and ellipticity. © 2012 American Physical Society.


Localized mode hybridization by fine tuning of twodimensional random media Labonté, L., C. Vanneste, and P. Sebbah Optics Letters 37, no. 11, 19461948 (2012)
Résumé: We study numerically the interaction of spatially localized modes in strongly scattering twodimensional (2D) media. We move eigenvalues in the complex plane by changing gradually the index of a single scatterer. When spatial and spectral overlap is sufficient, localized states couple, and avoided level crossing is observed. We show that local manipulation of the disordered structure can couple several localized states to form an extended chain of hybridized modes crossing the entire sample, thus changing the nature of certain modes from localized to extended in a nominally localized disordered system. We suggest such a chain in 2D random systems is the analog of onedimensional necklace states, the occasional open channels predicted by Pendry [Physics 1, 20 (2008).] through which the light can sneak through an opaque medium. © 2012 Optical Society of America.
Motsclés: Complex planes; Disordered structures; Disordered system; Eigenvalues; Fine tuning; Hybridized modes; Level crossing; Localized modes; Localized state; Open channels; Random media; Random systems; Spectral overlap; Eigenvalues and eigenfunctions; Two dimensional


Usual Anderson localization restored in bilayered left and righthanded structures Maurel, A., A. Ourir, J.F. Mercier, and V. Pagneux Physical Review B  Condensed Matter and Materials Physics 85, no. 20 (2012)
Résumé: We present a study of the attenuation length in a onedimensional array of alternating left and righthanded materials in which both the permittivities and the permeabilities are disordered. This type of structure has been shown to present an anomaly in the attenuation length when only permeabilities are disordered. We derive a simple analytical expression of the attenuation length, when the disorder in the refraction index is due to perturbations in both the permeability and the permittivity. Our expression is able to explain the transition to the anomalous behavior when perturbation only in the permeability or only in the permittivity is considered. Besides, we show that the anomaly is dramatically affected when considering perturbations in permeability and permittivity. The coupling effects are able to restore the ordinary localization length. © 2012 American Physical Society.


Absorption by an optical dipole antenna in a structured environment Castanié, E., R. Vincent, R. Pierrat, and R. Carminati International Journal of Optics 2012 (2012)
Résumé: We compute generalized absorption and extinction crosssections of an optical dipole nanoantenna in a structured environment. The expressions explicitly show the influence of radiation reaction and the local density of states on the intrinsic absorption properties of the antenna. Engineering the environment could allow to modify the overall absorption as well as the frequency and the linewidth of a resonant antenna. Conversely, a dipole antenna can be used to probe the photonic environment, in a similar way as a quantum emitter. Copyright © 2012 E. Castanié et al.


Propagation of guided waves through weak penetrable scatterers Maurel, A., and J.F. Mercier Journal of the Acoustical Society of America 131, no. 3, 18741889 (2012)
Résumé: The scattering of a scalar wave propagating in a waveguide containing weak penetrable scatterers is inspected in the Born approximation. The scatterers are of arbitrary shape and present a contrast both in density and in wavespeed (or bulk modulus), a situation that can be translated in the context of SH waves, water waves, or transverse electric/transverse magnetic polarized electromagnetic waves. For small size inclusions compared to the waveguide height, analytical expressions of the transmission and reflection coefficients are derived, and compared to results of direct numerical simulations. The cases of periodically and randomly distributed inclusions are considered in more detail, and compared with unbounded propagation through inclusions. Comparisons with previous results valid in the low frequency regime are proposed. © 2012 Acoustical Society of America.
Motsclés: Analytical expressions; Arbitrary shape; Low frequency; Polarized electromagnetic waves; Randomly distributed; Scalar waves; SH wave; Small size; Transmission and reflection coefficient; Transverse electrics; Wavespeed; Born approximation; Electromagnetic waves; Waveguides; Scattering


Source location from fluorescence lifetime in disordered media Irishina, N., M. Moscoso, and R. Carminati Optics Letters 37, no. 5, 951953 (2012)
Résumé: We show that the source location problem can be solved in a scattering medium using the fluorescence lifetime and realistic a priori information. The intrinsic illposedness of the problem is reduced when the level of scattering increases. This work is a proof of principle demonstrating the high potential of quantitative lifetime imaging in complex media. © 2012 Optical Society of America.
Motsclés: Complex media; Disordered media; Fluorescence lifetimes; High potential; Illposedness; Lifetime imaging; Priori information; Proof of principles; Scattering medium; Source location; Source location problem; Optics; Optoelectronic devices; Fluorescence


Timedomain radiation and absorption by subwavelength sources Bossy, E., and R. Carminati EuroPhysics Letters 97, no. 3, 34001 (2012)
Résumé: Radiation by elementary sources is a basic problem in wave physics. We show that the timedomain energy flux radiated from electromagnetic and acoustic subwalength sources exhibits remarkable features. In particular, a subtle tradeoff between source emission and absorption underlies the mechanism of radiation. This behavior should be observed for any kind of classical waves, thus having broad potential implications. We discuss the implication for subwavelength focusing by time reversal with active sources. Copyright © EPLA, 2012.


Fourier transform profilometry for water waves: How to achieve clean water attenuation with diffusive reflection at the water surface? Przadka, A., B. Cabane, V. Pagneux, A. Maurel, and P. Petitjeans Experiments in Fluids 52, no. 2, 519527 (2012)
Résumé: We present a study of the damping of capillarygravity waves in water containing pigments. The practical interest comes from a recent profilometry technique (FTP for Fourier Transform Profilometry) using fringe projection onto the liquidfree surface. This experimental technique requires diffusive reflection of light on the liquid surface, which is usually achieved by adding white pigments. It is shown that the use of most paint pigments causes a large enhancement of the damping of the waves. Indeed, these paints contain surfactants which are easily adsorbed at the airwater interface. The resulting surface film changes the attenuation properties because of the resonancetype damping between capillarygravity waves and Marangoni waves. We study the physicochemical properties of coloring pigments, showing that particles of the anatase (TiO 2) pigment make the water surface light diffusive while avoiding any surface film effects. The use of the chosen particles allows to perform spacetime resolved FTP measurements on capillarygravity waves, in a liquid with the damping properties of pure water. © 2011 SpringerVerlag.
Motsclés: Air water interfaces; Attenuation properties; Capillarygravity waves; Clean waters; Coloring pigments; Damping property; Experimental techniques; Fourier transform profilometry; Fringe projection; Liquid surface; Marangoni; Physicochemical property; Pure water; Reflection of light; Surface films; TiO; Water surface; White pigments; Damping; Gravity waves; Internet protocols; Paint; Profilometry; Surface active agents; Surface waters; Titanium dioxide; Liquids


Nonlinear effects in random lasers Andreasen, J., P. Sebbah, and C. Vanneste Journal of the Optical Society of America B: Optical Physics 28, no. 12, 29472955 (2011)
Résumé: Recent numerical and theoretical studies have demonstrated that the modes at threshold of a random laser are in direct correspondence with the resonances of the same system without gain, a feature which is well known in conventional lasers but not known until recently for random lasers. This paper presents numerical results of the multimode regime that takes place when the pumping rate is progressively increased above threshold. Behavior that is already known in standard lasers, such as mode competition and nonlinear wave mixing, are shown to also take place in random lasers thus reinforcing their recent modal description. However, due to the complexity of the laser modes and to the openness of such lasers, which require large external pumping to compensate for strong loss, one observes that these effects are systematic and can be more pronounced than in a conventional laser. © 2011 Optical Society of America.
Motsclés: Conventional lasers; Mode competition; Multimodes; Nonlinear effect; Nonlinear wave mixing; Numerical results; Pumping rate; Random lasers; Theoretical study; Laser beams; Pumping (laser)


CramerRao analysis of steadystate and timedomain fluorescence diffuse optical imaging Boffety, M., M. Allain, A. Sentenac, M. Massonneau, and R. Carminati Biomedical Optics Express 2, no. 6, 16261636 (2011)
Résumé: Using a CramerRao analysis, we study the theoretical performances of a time and spatially resolved fDOT imaging system for jointly estimating the position and the concentration of a pointwide fluorescent volume in a diffusive sample. We show that the fluorescence lifetime is a critical parameter for the precision of the technique. A time resolved fDOT system that does not use spatial information is also considered. In certain cases, a simple steadystate configuration may be as efficient as this time resolved fDOT system. © 2011 Optical Society of America.
Motsclés: Critical parameter; Diffuse optical imaging; Fluorescence lifetimes; Spatial informations; Spatially resolved; Theoretical performance; Time domain; Timeresolved; Fluorescence; Time domain analysis


Different regimes for water wave turbulence Cobelli, P., A. Przadka, P. Petitjeans, G. Lagubeau, V. Pagneux, and A. Maurel Physical Review Letters 107, no. 21 (2011)
Résumé: We present an experimental study on gravity capillary wave turbulence in water. By using spacetime resolved Fourier transform profilometry, the behavior of the wave energy density η k,ω2 in the 3D (k,ω) space is inspected for various forcing frequency bandwidths and forcing amplitudes. Depending on the bandwidth, the gravity spectral slope is found to be either forcing dependent, as classically observed in laboratory experiments, or forcing independent. In the latter case, the wave spectrum is consistent with the ZakharovFilonenko cascade predicted within wave turbulence theory. © 2011 American Physical Society.
Motsclés: Experimental studies; Forcing amplitudes; Forcing frequencies; Fourier transform profilometry; Gravity capillary waves; Laboratory experiments; Spectral slopes; Wave energy density; Wave spectra; Wave turbulence; Profilometry; Turbulence; Wave energy conversion; Bandwidth


Coherent flash of light emitted by a cold atomic cloud Chalony, M., R. Pierrat, D. Delande, and D. Wilkowski Physical Review A  Atomic, Molecular, and Optical Physics 84, no. 1 (2011)
Résumé: When a resonant laser sent on an optically thick cold atomic cloud is abruptly switched off, a coherent flash of light is emitted in the forward direction. This transient phenomenon is observed due to the highly resonant character of the atomic scatterers. We analyze quantitatively its temporal properties and show very good agreement with theoretical predictions. Based on complementary experiments, the phase of the coherent field is reconstructed without interferometric tools. © 2011 American Physical Society.
Motsclés: Atomic clouds; Coherent fields; Temporal property; Theoretical prediction; Transient phenomenon; Atoms


Longtail statistics of the purcell factor in disordered media driven by nearfield interactions Sapienza, R., P. Bondareff, R. Pierrat, B. Habert, R. Carminati, and N. F. Van Hulst Physical Review Letters 106, no. 16 (2011)
Résumé: In this Letter, we study the Purcell effect in a 3D disordered dielectric medium through fluorescence decay rates of nanosized light sources. We report distributions of Purcell factor with nonGaussian longtailed statistics and an enhancement of up to 8 times the average value. We attribute this large enhancement to strong fluctuations of the local density of states induced by nearfield scattering sustained by more than one particle. Our findings go beyond standard diagrammatic and singlescattering models and can be explained only by taking into account the full nearfield interaction. © 2011 American Physical Society.
Motsclés: Average values; Disordered dielectrics; Disordered media; Fluorescence decays; Local density of state; Nanosized; Near field interactions; Nearfield scattering; NonGaussian; Purcell effect; Purcell factor; Singlescattering model; Light sources; Dielectric materials


Magnetooptical control of Förster energy transfer Vincent, R., and R. Carminati Physical Review B  Condensed Matter and Materials Physics 83, no. 16 (2011)
Résumé: We introduce a general framework to study dipoledipole energy transfer between an emitter and an absorber in a nanostructured environment. The theory allows us to address Förster resonant energy transfer (FRET) between a donor and an acceptor in the presence of a nanoparticle with an anisotropic electromagnetic response. In the particular case of a magnetooptical anisotropy, we compute the generalized FRET rate and discuss the orders of magnitude. The distance dependence, the FRET efficiency, and the sensitivity to the orientation of the transition dipoles orientation differ from standard FRET and can be controlled using the static magnetic field as an external parameter. © 2011 American Physical Society.


Experimental study on waterwave trapped modes Cobelli, P. J., V. Pagneux, A. Maurel, and P. Petitjeans Journal of Fluid Mechanics 666, 445476 (2011)
Résumé: We present an experimental study on the trapped modes occurring around a vertical surfacepiercing circular cylinder of radius a placed symmetrically between the parallel walls of a long but finite water waveguide of width 2d. A wavemaker placed near the entrance of the waveguide is used to force an asymmetric perturbation into the guide, and the freesurface deformation field is measured using a global singleshot optical profilometric technique. In this configuration, several values of the aspect ratio a/d were explored for a range of driving frequencies below the waveguide's cutoff. Decomposition of the obtained fields in harmonics of the driving frequency allowed for the isolation of the linear contribution, which was subsequently separated according to the symmetries of the problem. For each of the aspect ratios considered, the spatial structure of the trapped mode was obtained and compared to the theoretical predictions given by a multipole expansion method. The waveguide'obstacle system was further characterized in terms of reflection and transmission coefficients, which led to the construction of resonance curves showing the presence of one or two trapped modes (depending on the value of a/d), a result that is consistent with the theoretical predictions available in the literature. The frequency dependency of the trapped modes with the geometrical parameter a/d was determined from these curves and successfully compared to the theoretical predictions available within the frame of linear wave theory. © 2011 Cambridge University Press.
Motsclés: surface gravity waves; wave scattering; wave'structure interactions; Asymmetric perturbations; Driving frequencies; Experimental studies; Freesurface deformation; Frequency dependencies; Geometrical parameters; Linear contribution; Linear wave theory; Multipole expansion methods; Reflection and transmission coefficients; Resonance curves; Singleshot; Spatial structure; Surface gravity waves; Theoretical prediction; Trapped modes; Vertical surface; wave scattering; Wavemakers; Circular cylinder


Waves around almost periodic arrangements of scatterers: Analysis of positional disorder Martin, P. A., and A. Maurel Mathematical Methods in the Applied Sciences 33, no. 18, 22152224 (2010)
Résumé: Much is known about the propagation of waves through periodic arrangements of identical scatterers, such as through a photonic crystal. Here, we consider a simple realization: scalar waves through a regular twodimensional array of identical small circles. We are interested in the effect of random disorder: the circles remain identical, but their centres are given small random displacements. We derive asymptotic approximations that can be used to quantify the effect of positional disorder. Extension to more complicated problems seems feasible and is expected. Copyright © 2010 John Wiley & Sons, Ltd.
Motsclés: acoustics; photonic crystals; QCA; Almost periodic; Asymptotic approximation; Positional disorder; QCA; Random disorders; Random displacement; Scalar waves; Twodimensional arrays; Photonic crystals


Effective propagation in a onedimensional perturbed periodic structure: Comparison of several approaches Maurel, A., P. A. Martin, and V. Pagneux Waves in Random and Complex Media 20, no. 4, 634655 (2010)
Résumé: Acoustic scattering by an ensemble of scatterers whose positions are close to the positions of a periodic arrangement (with small and random perturbations in the position of each scatterer) is considered in one dimension. Three methods are compared to obtain the effective wavenumber of the coherent field. The first two methods, the quasicrystalline approximation (QCA) and the coherent potential approximation (CPA), give the exact Floquet solution in the periodic case. However, in a perturbed almost periodic configuration, they give different dispersion relations. These methods are compared to a perturbation approach and confronted with the results obtained from direct numerical calculations. It is shown that CPA is able to get the first correction to the Floquet dispersion relation due to the introduced perturbation, in agreement with the perturbation approach and with direct numerical results, while QCA is unable to get this correction. © 2010 Taylor & Francis.
Motsclés: Acoustic Scattering; Almost periodic; Coherent fields; Coherentpotential approximation; Dispersion relations; Floquet; Numerical calculation; Numerical results; One dimension; Perturbation approach; Random perturbations; Wave numbers; Dispersion (waves); Green's function; Numerical methods; Quantum theory; Scattering; Periodic structures


Flower patterns in drop impact on thin liquid films Lagubeau, G., M. A. Fontelos, C. Josserand, A. Maurel, V. Pagneux, and P. Petitjeans Physical Review Letters 105, no. 18 (2010)
Résumé: We describe experimentally the formation of a pattern for drop impacts on thin liquid films for a large range of impact parameters. Using the shallowwater approximation, we are able to explain the main mechanisms leading to these patterns: it consists in the linear instability of the selfsimilar axisymmetric radial solution of the equations. Agreement between the experiments and the theory is remarkably good, leading, in particular, to the prediction that the most unstable fold number scales like (We/h∞)2/7. © 2010 The American Physical Society.
Motsclés: Axisymmetric; Drop Impact; Fold number; Impactparameter; Linear instabilities; Radial solutions; Selfsimilar; Shallowwater; Thin liquid film; Liquid films; Drops


Fluctuations of the local density of states probe localized surface plasmons on disordered metal films Krachmalnicoff, V., E. Castanié, Y. De Wilde, and R. Carminati Physical Review Letters 105, no. 18 (2010)
Résumé: We measure the statistical distribution of the local density of optical states (LDOS) on disordered semicontinuous metal films. We show that LDOS fluctuations exhibit a maximum in a regime where fractal clusters dominate the film surface. These large fluctuations are a signature of surfaceplasmon localization on the nanometer scale. © 2010 The American Physical Society.
Motsclés: Disordered metals; Film surfaces; Fractal clusters; Local density; Local density of state; Localized surface plasmon; Nanometer scale; Optical state; Semicontinuous metal films; Statistical distribution; Surfaceplasmon; Metallic films; Plasmons; Optical data storage


Nearfield interactions and nonuniversality in speckle patterns produced by a point source in a disordered medium Cazé, A., R. Pierrat, and R. Carminati Physical Review A  Atomic, Molecular, and Optical Physics 82, no. 4 (2010)
Résumé: A point source in a disordered scattering medium generates a speckle pattern with nonuniversal features, giving rise to the socalled C0 correlation. We analyze theoretically the relationship between the C0 correlation and the statistical fluctuations of the local density of states, based on simple arguments of energy conservation. This derivation leads to a clear physical interpretation of the C0 correlation. Using exact numerical simulations, we show that C0 is essentially a correlation resulting from nearfield interactions. These interactions are responsible for the nonuniversality of C0 that confers to this correlation a huge potential for sensing and imaging at the subwavelength scale in complex media. © 2010 The American Physical Society.
Motsclés: Complex media; Disordered medium; Local density of state; Near field interactions; Nonuniversality; Numerical simulation; Physical interpretation; Point sources; Scattering medium; Sensing and imaging; Speckle patterns; Statistical fluctuations; Subwavelength scale; Ferroelectric materials; Speckle; Correlation methods


Reflection and transmission by a slab with randomly distributed isotropic point scatterers Maurel, A. Journal of Computational and Applied Mathematics 234, no. 6, 18421850 (2010)
Résumé: The problem of how a wave propagates in an infinite medium filled with scatterers has revealed the notion of an effective medium: the mean wave propagates as in an homogeneous medium with complex index. Is this notion of an effective medium still valid when the scatterers are bounded in space? The problem is treated here for isotropic point scatterers. It is shown that (i) the waves propagate inside the slab with an effective wavenumber K being the same as that in an infinite medium, (ii) the reflection and transmission coefficients of the slab mainly behave as R≃(1eiKL)(kK)2k and T≃eiKL at leading order, (iii) the reflection and transmission coefficients of a single interface are related to R and T with the usual law of optics and (iv) the boundary conditions to be applied at the interface are the continuity of the field and its first derivative for isotropic scatterers. Finally, numerical experiments in one dimension show satisfactory agreement with the presented theory. © 2009 Elsevier B.V.
Motsclés: Multiple scattering; Random media; Reflection & transmission; Complex indices; Effective medium; First derivative; Homogeneous medium; Isotropic points; Leading orders; Numerical experiments; One dimension; Random media; Randomly distributed; Reflection and transmission; Reflection and transmission coefficients; Wave numbers; Multiple scattering; Random processes; Reflection


Estimating the dynamic effective mass density of random composites Martin, P. A., A. Maurel, and W. J. Parnell Journal of the Acoustical Society of America 128, no. 2, 571577 (2010)
Résumé: The effective mass density of an inhomogeneous medium is discussed. Random configurations of circular cylindrical scatterers are considered, in various physical contexts: fluid cylinders in another fluid, elastic cylinders in a fluid or in another solid, and movable rigid cylinders in a fluid. In each case, timeharmonic waves are scattered, and an expression for the effective wavenumber due to Linton and Martin [J. Acoust. Soc. Am. 117, 34133423 (2005)] is used to derive the effective density in the low frequency limit, correct to second order in the area fraction occupied by the scatterers. Expressions are recovered that agree with either the Ament formula or the effective static mass density, depending upon the physical context. © 2010 Acoustical Society of America.
Motsclés: Area fraction; Effective density; Effective mass density; Elastic cylinders; Inhomogeneous medium; Low frequency limits; Mass densities; Random composites; Random configurations; Rigid cylinder; Second orders; Timeharmonic waves; Wave numbers; Fluids; Circular cylinders; acoustics; article; motion; pressure; statistical model; theoretical model; Young modulus; Acoustics; Elastic Modulus; Linear Models; Models, Theoretical; Motion; Pressure


Number of propagating modes of a diffusive periodic waveguide in the semiclassical limit Barra, F., A. Maurel, V. Pagneux, and J. Zuñiga Physical Review E  Statistical, Nonlinear, and Soft Matter Physics 81, no. 6 (2010)
Résumé: We study the number of propagating Bloch modes NB of an infinite periodic billiard chain. The asymptotic semiclassical behavior of this quantity depends on the phasespace dynamics of the unit cell, growing linearly with the wave number k in systems with a nonnull measure of ballistic trajectories and going like ∼√k in diffusive systems. We have calculated numerically NB for a waveguide with cosineshaped walls exhibiting strongly diffusive dynamics. The semiclassical prediction for diffusive systems is verified to good accuracy and a connection between this result and the universality of the parametric variation of energy levels is presented. © 2010 The American Physical Society.
Motsclés: Ballistic trajectories; Bloch modes; Diffusive dynamics; Diffusive system; Energy level; Parametric variation; Periodic waveguides; Phasespace dynamics; Propagating mode; Semiclassical limit; Unit cells; Wave numbers; Phase space methods; Waveguides


Theory of infrared nanospectroscopy by photothermal induced resonance Dazzi, A., F. Glotin, and R. Carminati Journal of Applied Physics 107, no. 12 (2010)
Résumé: We present a theoretical investigation of the physics involved in a recently developed spectromicroscopy technique, called photothermal induced resonance (PTIR). With this technique, one measures the local infrared absorption spectrum of a sample shined with a tunable infrared laser pulse, and detects the induced photothermal expansion with the tip of an atomic force microscope (AFM). Simple physical assumptions allow us to describe analytically the heating and expansion of the sample, the excitation of the vibration modes of the AFM cantilever, and the detected signal. We show that the signal depends on the thermal expansion velocity rather than on the absolute displacement of the tip, and we investigate the influence of the laser pulse length. Eventually, we express the PTIR signal in terms of relevant parameters, and prove its proportionality to the sample absorbance. This analytical approach complement our experimental results and validates the PTIR method as a technique of choice for infrared spectroscopy of nanoscopic samples, getting around optical artifacts like reflectance perturbation. © 2010 American Institute of Physics.
Motsclés: Absolute displacement; Absorbances; AFM cantilevers; Analytical approach; Atomic force microscopes; Photothermal; Photothermal expansion; Physical assumptions; Spectromicroscopy; Theoretical investigations; Tunable infrared laser; Vibration modes; Absorption spectroscopy; Atomic force microscopy; Atomic spectroscopy; Infrared lasers; Infrared spectroscopy; Laser pulses; Photolithography; Pulsed laser applications; Resonance; Vibration analysis; Thermal expansion


Spontaneous decay rate of a dipole emitter in a strongly scattering disordered environment Pierrat, R., and R. Carminati Physical Review A  Atomic, Molecular, and Optical Physics 81, no. 6 (2010)
Résumé: We study the statistics of the fluorescence decay rate of a dipole emitter embedded in a strongly scattering medium. In the multiplescattering regime, the probability of observing a decrease in the decay rate is substantial, as predicted by exact numerical simulations. The decrease originates from a reduction of the local density of optical states and is due to collective interactions and interferences. In the strongscattering regime, signatures of recurrent scattering are visible in the behavior of the average decay rate. © 2010 The American Physical Society.
Motsclés: Decay rate; Fluorescence decays; Local density; Numerical simulation; Optical state; Scattering medium; Scattering regime; Spontaneous decay rates; Computer simulation; Decay (organic); Optical waveguides; Scattering


Subwavelength spatial correlations in nearfield speckle patterns Carminati, R. Physical Review A  Atomic, Molecular, and Optical Physics 81, no. 5 (2010)
Résumé: At subwavelength distance from the exit surface of a disordered medium, speckle patterns generated by multiple scattering of waves exhibit nonuniversal nearfield correlations. A calculation of the field spatial correlation function shows that the correlation length is driven by the microscopic structure of the medium. The averaged speckle spot size can be smaller than the wavelength, even for nonresonant dielectric media. © 2010 The American Physical Society.
Motsclés: Correlation lengths; Disordered medium; Microscopic structures; Nearfield; Nearfield speckles; Nonresonant dielectrics; Spatial correlation functions; Spatial correlations; Speckle patterns; Spot sizes; Subwavelength; Speckle


Measuring the transmission matrix in optics: An approach to the study and control of light propagation in disordered media Popoff, S. M., G. Lerosey, R. Carminati, M. Fink, A. C. Boccara, and S. Gigan Physical Review Letters 104, no. 10 (2010)
Résumé: We introduce a method to experimentally measure the monochromatic transmission matrix of a complex medium in optics. This method is based on a spatial phase modulator together with a fullfield interferometric measurement on a camera. We determine the transmission matrix of a thick random scattering sample. We show that this matrix exhibits statistical properties in good agreement with random matrix theory and allows light focusing and imaging through the random medium. This method might give important insight into the mesoscopic properties of a complex medium. © 2010 The American Physical Society.
Motsclés: Complex medium; Disordered media; Fullfield; Interferometric measurement; matrix; Mesoscopic properties; Random matrix theory; Random medium; Random scattering; Spatial phase modulator; Statistical properties; Transmission matrix; Light; Light propagation; Light transmission


Controlling the quantum yield of a dipole emitter with coupled plasmonic modes Vandenbem, C., D. Brayer, L. S. FroufePérez, and R. Carminati Physical Review B  Condensed Matter and Materials Physics 81, no. 8 (2010)
Résumé: We study theoretically the possibility of controlling the quantum yield of a single dipole emitter using coupled plasmonic modes. Plasmon hybridization offers spectral and spatial degrees of freedom that can be used to tune the spontaneous decay rate and the apparent quantum yield with high sensitivity. We demonstrate this concept on simple structures that could be implemented experimentally. © 2010 The American Physical Society.


Radiative corrections to the polarizability tensor of an electrically small anisotropic dielectric particle Albaladejo, S., R. GómezMedina, L. S. FroufePérez, H. Marinchio, R. Carminati, J. F. Torrado, G. Armelles, A. GarcíaMartín, and J. J. Sáenz Optics Express 18, no. 4, 35563567 (2010)
Résumé: Radiative corrections to the polarizability tensor of isotropic particles are fundamental to understand the energy balance between absorption and scattering processes. Equivalent radiative corrections for anisotropic particles are not well known. Assuming that the polarization within the particle is uniform, we derived a closedform expression for the polarizability tensor which includes radiative corrections. In the absence of absorption, this expression of the polarizability tensor is consistent with the optical theorem. An analogous result for infinitely long cylinders was also derived. Magneto optical Kerr effects in nonabsorbing nanoparticles with magnetooptical activity arise as a consequence of radiative corrections to the electrostatic polarizability tensor. © 2010 Optical Society of America.
Motsclés: Anisotropic dielectrics; Anisotropic particles; Closedform expression; Isotropic particles; Magnetooptical activity; Magnetooptical Kerr effects; Optical theorem; Polarizability tensor; Radiative corrections; Scattering process; Absorption; Anisotropy; Gene expression; High energy physics; Kerr magnetooptical effect; Magnetic field effects; Magnetos; Tensors; Optical Kerr effect; anisotropy; article; computer simulation; electromagnetic field; impedance; particle size; radiation dose; radiati


Towards a random laser with cold atoms Guerin, W., N. Mercadier, F. Michaud, D. Brivio, L. S. FroufePérez, R. Carminati, V. Eremeev, A. Goetschy, S. E. Skipetrov, and R. Kaiser Journal of Optics A: Pure and Applied Optics 12, no. 2 (2010)
Résumé: Atoms can scatter light and they can also amplify it by stimulated emission. From this simple starting point, we examine the possibility of realizing a random laser in a cloud of lasercooled atoms. The answer is not obvious as both processes (elastic scattering and stimulated emission) seem to exclude one another: pumping atoms to make them behave as an amplifier drastically reduces their scattering crosssection. However, we show that even the simplest atom model allows the efficient combination of gain and scattering. Moreover, the supplementary degrees of freedom that atoms offer allow the use of several gain mechanisms, depending on the pumping scheme. We thus first study these different gain mechanisms and show experimentally that they can induce (standard) lasing. We then present how the constraint of combining scattering and gain can be quantified, which leads to an evaluation of the random laser threshold. The results are promising and we draw some prospects for a practical realization of a random laser with cold atoms. © 2010 IOP Publishing Ltd.
Motsclés: Cold atoms; Random laser; Cold atoms; Degrees of freedom; Lasercooled atoms; Practical realizations; Pumping schemes; Random lasers; Scattering cross section; Degrees of freedom (mechanics); Laser beams; Pumps; Scattering; Stimulated emission; Atoms


Fluorescence quenching by a metal nanoparticle in the extreme nearfield regime Castanié, E., M. Boffety, and R. Carminati Optics Letters 35, no. 3, 291293 (2010)
Résumé: We study the spontaneous decay rate of a dipóle emitter close to a metallic nanoparticle in the extreme nearfield regime. The metal is modeled using a nonlocal dielectric function that accounts for the microscopic length scales of the free electron gas. We describe quantitatively the crossover between the macroscopic and microscopic regimes and the enhanced nonradiative decay due to microscopic interactions. Our theory is in agreement with results previously established in the asymptotic near and farfield regimes. © 2010 Optical Society of America.
Motsclés: Dielectric functions; Farfield; Fluorescence quenching; Free electron gas; Metal nanoparticles; Metallic nanoparticles; Microscopic interaction; Microscopic length scale; Nearfield; Nonlocal; Nonradiative decays; Spontaneous decay rates; Decay (organic); Electron gas; Nanoparticles


Surface acoustic waves in interaction with a dislocation Maurel, A., V. Pagneux, F. Barra, and F. Lund Ultrasonics 50, no. 2, 161166 (2010)
Résumé: A surface acoustic wave can interact with dislocations that are close to the surface. We characterize this interaction and its manifestations as scattered surface acoustic waves for different orientations with respect to the surface of an edge dislocation. For dislocations that are parallel or perpendicular to the free surface, we present an analytical result for short dislocations with respect to the wavelength that reproduce qualitatively the main features observed for dislocations of various sizes. © 2009 Elsevier B.V. All rights reserved.
Motsclés: Dislocations; Scattering; Surface acoustic waves; Analytical results; Edge dislocation; Free surfaces; Scattering surface; Surface acoustic waves; Acoustic surface wave devices; Acoustic waves; Acoustics; Acoustoelectric effects; Acoustic wave scattering


Fluorescence signal of a single emitter coupled to a nanoparticle through a plasmonic film Vandenbem, C., L. S. FroufePérez, and R. Carminati Journal of Optics A: Pure and Applied Optics 11, no. 11 (2009)
Résumé: We study theoretically the detection of the fluorescence intensity emitted by a single emitter coupled to a nanoparticle through a metallic thin film. The coupling results from the overlap of the surface plasmon modes propagating on each interface of the film. We show that the distance between the nanoparticle and the film can be used to tune the apparent quantum yield and the radiation pattern with nanometerscale sensitivity. Such a system is appealing from the experimental point of view since it involves simple structures that can be controlled using current scanning nearfield optical techniques. It could be used to improve the detection sensitivity of molecules embedded in substrates, or to design sensitive biological or chemical plasmonic sensors. © 2009 IOP Publishing Ltd.
Motsclés: Fluorescence; Molecular imaging; Plasmons; Quenching; Single molecule; Detection sensitivity; Fluorescence intensities; Fluorescence molecular; Fluorescence signals; Metallic thin films; Molecular imaging; Nanometerscale; Nearfield; Optical technique; Plasmonic sensors; Radiation patterns; Simple structures; Single emitter; Single molecule; Surface plasmon modes; Fluorescence; Molecules; Optical data storage; Plasmons; Quenching; Nanoparticles


Spacetime resolved wave turbulence in a vibrating plate Cobelli, P., P. Petitjeans, A. Maurel, V. Pagneux, and N. Mordant Physical Review Letters 103, no. 20 (2009)
Résumé: Wave turbulence in a thin elastic plate is experimentally investigated. By using a Fourier transform profilometry technique, the deformation field of the plate surface is measured simultaneously in time and space. This enables us to compute the wavevectorfrequency (k, ω) Fourier spectrum of the full spacetime deformation velocity. In the 3D (k, ω) space, we show that the energy of the motion is concentrated on a 2D surface that represents a nonlinear dispersion relation. This nonlinear dispersion relation is close to the linear dispersion relation. This validates the usual wavenumberfrequency change of variables used in many experimental studies of wave turbulence. The deviation from the linear dispersion, which increases with the input power of the forcing, is attributed to weak nonlinear effects. Our technique opens the way for many new extensive quantitative comparisons between theory and experiments of wave turbulence. © 2009 The American Physical Society.
Motsclés: Deformation field; Elastic plate; Experimental studies; Fourier spectra; Fourier transform profilometry; Frequency changes; Input power; Linear dispersion; Linear dispersion relations; Nonlinear dispersion relation; Nonlinear effect; Plate surfaces; Quantitative comparison; Time and space; Time deformation; Timeresolved; Vibrating plate; Wave numbers; Wave turbulence; Wave vector; Deformation; Dispersions; Fourier transforms; Profilometry; Quantum theory; Turbulence; Two dimensional; Dispersion


Reply to "comment on 'Interaction of a surface wave with a dislocation'" Maurel, A., V. Pagneux, F. Barra, and F. Lund Physical Review B  Condensed Matter and Materials Physics 80, no. 13 (2009)
Résumé: A subsurface moving dislocation in an elastic half space generates vertical displacements at the free surface. We compare this displacement for two different values of the dislocation viscous drag coefficient. The different resulting surface patterns suggest the free surface plays a decisive dynamical effect. We thus compare this displacement, using the dynamic Green function for an elastic half space, with the result of the calculation using the static Green function for an infinite space, as in the work of Zolotoyabko and Shilo [preceding paper, Phys. Rev. B 80, 136101 (2009), and Shilo and Zolotoyabko, Phys. Rev. Lett. 91, 115506 (2003)] when the dislocation dynamics is the same. Considering the static Green function of an infinite space instead of the correct dynamic Green function of the half space leads to an underestimation of the resulting displacement at the free surface by a factor up to 50 for dislocation depths smaller than one Rayleigh wavelength λR. We also discuss the constraints that recent ultrasound attenuation and resonant ultrasound spectroscopy experiments place on dislocation parameters, such as density and viscous drag coefficient. © 2009 The American Physical Society.


Experimental observation of trapped modes in a water wave channel Cobelli, P. J., V. Pagneux, A. Maurel, and P. Petitjeans Europhysics Letters 88, no. 2 (2009)
Résumé: The fluid around a free surface piercing circular cylinder in a long narrow wave tank can exhibit a local oscillation that does not propagate down the channel but is confined to the vicinity of the cylinder. This is a manifestation of the socalled trapped modes, bound states in the continuum occurring in many situations in physics. In this letter, using Fourier Transform Profilometry, fully space time resolved measurements for the free surface deformation are obtained. The scattering characteristics of the cylinder and consequently the behavior of the trappedmode frequency are determined. Copyright © EPLA, 2009.


Interaction between elastic waves and prismatic dislocation loops Rodríguez, N., A. Maurel, V. Pagneux, F. Barra, and F. Lund Journal of Applied Physics 106, no. 5 (2009)
Résumé: The properties of prismatic dislocation loops, generated by radiation in metals, have remained elusive for decades, and recent advances in computational capabilities as well as transmission electron microscopy have renewed interest in their study. Acoustic and elastic waves could become an interesting, nonintrusive, probe to this end, as they have for other dislocation configurations. What then are the characteristics of elastic wave scattering that would be sensitive to a prismatic loop signature? In this paper, we report the scattering cross section for an elastic wave by a prismatic dislocation loop. It differs in significant ways from the analog quantity in the case of pinned dislocation segments, the most significant being the polarization of the scattered wave. The properties of a coherent wave traveling through an elastic medium filled with randomly placed and randomly oriented such loops are also reported. At long wavelengths, the effective wave velocity and attenuation coefficients resemble those for a similar case with pinned dislocation segments. © 2009 American Institute of Physics.
Motsclés: Attenuation coefficient; Coherent waves; Computational capability; Dislocation configurations; Dislocation segments; Elastic medium; Elastic wave scattering; Long wavelength; Nonintrusive; Prismatic dislocation loop; Scattered waves; Scattering cross section; Similar case; Wave velocity; Elastic waves; Elasticity; Soil structure interactions; Transmission electron microscopy; Waves


Ultrasound as a probe of plasticity? the interaction of elastic waves with dislocations Maurel, A., V. Pagneux, F. Barra, and F. Lund International Journal of Bifurcation and Chaos 19, no. 8, 27652781 (2009)
Résumé: An overview of recent work on the interaction of elastic waves with dislocations is given. The perspective is provided by the wish to develop nonintrusive tools to probe plastic behavior in materials. For simplicity, ideas and methods are first worked out in two dimensions, and the results in three dimensions are then described. These results explain a number of recent, hitherto unexplained, experimental findings. The latter include the frequency dependence of ultrasound attenuation in copper, the visualization of the scattering of surface elastic waves by isolated dislocations in LiNbO 3, and the ratio of longitudinal to transverse wave attenuation in a number of materials. Specific results reviewed include the scattering amplitude for the scattering of an elastic wave by a screw, as well as an edge, dislocation in two dimensions, the scattering amplitudes for an elastic wave by a pinned dislocation segment in an infinite elastic medium, and the wave scattering by a subsurface dislocation in a semiinfinite medium. Also, using a multiple scattering formalism, expressions are given for the attenuation coefficient and the effective speed for coherent wave propagation in the cases of antiplane waves propagating in a medium filled with many, randomly placed screw dislocations; inplane waves in a medium similarly filled with randomly placed edge dislocations with randomly oriented Burgers vectors; elastic waves in a threedimensional medium filled with randomly placed and oriented dislocation line segments, also with randomly oriented Burgers vectors; and elastic waves in a model threedimensional polycrystal, with only low angle grain boundaries modeled as arrays of dislocation line segments. © 2009 World Scientific Publishing Company.
Motsclés: Dislocations; Elastic waves; Plasticity; Antiplane wave; Attenuation coefficient; Coherent waves; Dislocation lines; Dislocation segments; Dislocations; Edge dislocation; Elastic medium; Frequency dependence; Inplane; Low angle grain boundaries; Nonintrusive tools; Plastic behavior; Scattering amplitudes; Screw dislocations; Semiinfinite medium; Subsurfaces; Three dimensions; Transverse waves; Twodimension; Ultrasound attenuation; Wave scattering; Acoustic waves; Grain boundaries; Plastici


Global measurement of water waves by Fourier transform profilometry Cobelli, P. J., A. Maurel, V. Pagneux, and P. Petitjeans Experiments in Fluids 46, no. 6, 10371047 (2009)
Résumé: In this paper, we present an optical profilometric technique that allows for singleshot global measurement of freesurface deformations. This system consists of a highresolution system composed of a videoprojector and a digital camera. A fringe pattern of known characteristics is projected onto the free surface and its image is registered by the camera. The deformed fringe pattern arising from the surface deformations is later compared to the undeformed (reference) one, leading to a phase map from which the free surface can be reconstructed. Particularly, we are able to project wavelengthcontrolled sinusoidal fringe patterns, which considerably increase the overall performance of the technique and the quality of the reconstruction compared to that obtained with a Ronchi grating. In comparison to other profilometric techniques, it allows for singleshot nonintrusive measurement of surface deformations over large areas. In particular, our measurement system and analysis technique is able to measure free surface deformations with sharp slopes up to 10 with a 0.2 mm vertical resolution over an interrogation window of size 450 × 300 mm2 sampled on approximately 6.1 × 106 measurement points. Some illustrative examples of the application of this measuring system to fluid dynamics problems are presented. © 2009 SpringerVerlag.
Motsclés: Analysis techniques; Fourier transform profilometry; Free surface deformations; Free surfaces; Freesurface deformation; Fringe pattern; Global measurements; Highresolution systems; Illustrative examples; Interrogation window; Measurement points; Measurement system; Measuring systems; Nonintrusive measurements; Phase maps; Ronchi grating; Singleshot; Surface deformation; Vertical resolution; Cameras; Moire fringes; Profilometry; Surfaces; Deformation


Threshold of a random laser with cold atoms FroufePérez, L. S., W. Guerin, R. Carminati, and R. Kaiser Physical Review Letters 102, no. 17 (2009)
Résumé: We address the problem of achieving an optical random laser with a cloud of cold atoms, in which gain and scattering are provided by the same atoms. The lasing threshold can be defined using the onresonance optical thickness b0 as a single critical parameter. We predict the threshold quantitatively, as well as power and frequency of the emitted light, using two different light transport models and the atomic polarizability of a strongly pumped twolevel atom. We find a critical b0 on the order of 300, which is within reach of stateoftheart coldatom experiments. Interestingly, we find that random lasing can already occur in a regime of relatively low scattering. © 2009 The American Physical Society.
Motsclés: Atomic polarizability; Cold atoms; Critical parameter; Emitted light; Lasing threshold; Light transport model; Optical thickness; Random lasers; Random lasing; Twolevel atom; Laser beams; Atoms


Density of states and extinction mean free path of waves in random media: Dispersion relations and sum rules Carminati, R., and J. J. Sáenz Physical Review Letters 102, no. 9 (2009)
Résumé: We establish a fundamental relationship between the averaged local density of states and the extinction mean free path of waves propagating in random media. From the principle of causality and the KramersKronig relations, we show that both quantities are connected by dispersion relations and are constrained by a frequency sum rule. The results should be helpful in the analysis of wave transport through complex media and in the design of materials with specific transport properties. © 2009 The American Physical Society.
Motsclés: Transport properties; Complex medias; Density of state; Dispersion relations; KramersKronig relations; Local density of state; Mean free paths; Random medias; Sum rules; Wave transports; Quantum theory


Experimental and theoretical inspection of the phasetoheight relation in fourier transform profilometry Maurel, A., P. Cobelli, V. Pagneux, and P. Petitjeans Applied Optics 48, no. 2, 380392 (2009)
Résumé: The measurement of an object's shape using projected fringe patterns needs a relation between the measured phase and the object's height. Among various methods, the Fourier transform profilometry proposed by Takeda and Mutoh [Appl. Opt. 22, 39773982 (1983)] is widely used in the literature. Rajoub et al. have shown that the reference relation given by Takeda is erroneous [J. Opt. A. Pure Appl. Opt. 9, 6675 (2007)]. This paper follows from Rajoub's study. Our results for the phase agree with Rajoub's results for both paralleland crossedoptícalaxes geometries and for either collimated or noncollimated projection. Our two main results are: (i) we show experimental evidence of the error in Takeda's formula and (ii) we explain the error in Takeda's derivation and we show that Rajoub's argument concerning Takeda's error is not correct. © 2009 Optical Society of America.
Motsclés: Experimental evidences; Fouriertransform profilometries; Projected fringes; Profilometry; Fourier transforms


Analysis of the depth resolution limit of luminescence diffuse optical imaging Boffety, M., M. Allain, A. Sentenac, M. Massonneau, and R. Carminati Optics Letters 33, no. 20, 22902292 (2008)
Résumé: We introduce a methodology to determine quantitatively the depth resolution limit in luminescence diffuse optical imaging. The approach is based on a CramerRao statistical analysis, a noise model, and calculations of photon transport in tissues. We illustrate the method in the case of luminescence imaging in a brainskull model, showing its potential applications in molecular imaging on small animals. © 2008 Optical Society of America.
Motsclés: Light emission; Luminescence; Optical image storage; Optical variables measurement; Depth resolutions; Diffuse optical imaging; Luminescence imaging; Molecular imaging; Noise models; Photon transports; Potential applications; Skull models; Small animals; Statistical analysis; Light sources


Controlling the fluorescence lifetime of a single emitter on the nanoscale using a plasmonic superlens FroufePérez, L. S., and R. Carminati Physical Review B  Condensed Matter and Materials Physics 78, no. 12 (2008)
Résumé: Coupling a single dipole emitter to a metallic nanoparticle through the optical modes of a planar superlens made of lefthanded material can lead to substantial modifications of its spontaneous decay rate. We provide a quantitative study based on exact numerical simulation and show that such a scheme could allow the detection, the localization, and the control of the emitter dynamics with nanometerscale sensitivity, as well as the determination of its transition dipole orientation. © 2008 The American Physical Society.


Multiple scattering by random configurations of circular cylinders: Weak scattering without closure assumptions Martin, P. A., and A. Maurel Wave Motion 45, no. 78, 865880 (2008)
Résumé: Acoustic scattering by random collections of identical circular cylinders is considered. Each cylinder is penetrable, with a soundspeed that is close to that in the exterior: the scattering is said to be "weak". Two classes of methods are used. The first is usually associated with the names of Foldy and Lax. Such methods require a "closure assumption", in addition to the governing equations. The second class is based on iterative approximations to integral equations of LippmannSchwinger type. Such methods do not use a closure approximation. Our main result is that both approaches lead to exactly the same formulas for the effective wavenumber, correct to secondorder in scattering strength and secondorder in filling fraction. Approximations for the average wavefield are also derived and compared. © 2008 Elsevier B.V. All rights reserved.
Motsclés: Acoustic waves; Closure assumptions; LippmannSchwinger equation; Multiple scattering; Random media; Circular cylinders; Cylinders (shapes); Integral equations; Scattering; Acoustic Scattering; Acoustic waves; Closure approximation; Closure assumptions; Filling fractions; Governing equations; Iterative approximations; LippmannSchwinger equation; Multiple scattering; Random configurations; Random media; Scattering strength; Second orders; Wave numbers; Acoustic wave scattering; acoustic wave; cy


Effective propagation in a perturbed periodic structure Maurel, A., and V. Pagneux Physical Review B  Condensed Matter and Materials Physics 78, no. 5 (2008)
Résumé: In a recent paper inspected the effective parameters of a cluster containing an ensemble of scatterers with a periodic or a weakly disordered arrangement. A small amount of disorder is shown to have a small influence on the characteristics of the acoustic wave propagation with respect to the periodic case. In this Brief Report, we inspect further the effect of a deviation in the scatterer distribution from the periodic distribution. The quasicrystalline approximation is shown to be an efficient tool to quantify this effect. An analytical formula for the effective wave number is obtained in onedimensional acoustic medium and is compared with the Berryman result in the lowfrequency limit. Direct numerical calculations show a good agreement with the analytical predictions. © 2008 The American Physical Society.


Lifetime fluctuations of a single emitter in a disordered nanoscopic system: The influence of the transition dipole orientation FroufePérez, L. S., and R. Carminati Physica Status Solidi (A) Applications and Materials Science 205, no. 6, 12581265 (2008)
Résumé: We study the fluctuations of the fluorescence decay rate of a single emitter in a random cluster of nanoparticles, in a regime dominated by nearfield scattering. Configurational changes of the environment induce statistical changes of the decay rate. Two regimes are considered which differ in terms of transition dipole orientation. In one regime, the orientation of the transition dipole is assumed to remain constant while the configuration of the cluster changes randomly. In another regime, the orientation of the transition dipole is assumed unknown and continuously averaged over the three directions of space. Using exact numerical simulations and a simple analytical model, we show that the statistical distributions of the spontaneous decay rate are substantially different in both regimes. In both cases, the decay rate fluctuations are strongly dependent on the level of absorption at the nanoscale. We discuss the impact of this result in terms of imaging in complex media. © 2008 WILEYVCH Verlag GmbH & Co. KGaA.
Motsclés: Analytical models; Complex medias; Decay rates; Fluorescence decay rates; Imaging; Nanoscale; Nanoscopic systems; Nearfield; Numerical simulations; Random clusters; Spontaneous decay rates; Statistical distributions; Three directions; Transition dipoles; Absorption; Computer simulation; Molecular vibrations; Nanotechnology; Optical waveguides; Statistical methods; Decay (organic)


Theory of the time reversal cavity for electromagnetic fields Carminati, R., R. Pierrat, J. De Rosny, and M. Fink Optics Letters 32, no. 21, 31073109 (2007)
Résumé: We derive a general expression of the electric dyadic Green function in a timereversal cavity, based on vector diffraction theory in the frequency domain. Our theory gives a rigorous framework to timereversal experiments using electromagnetic waves and suggests a methodology to design structures generating subwavelength focusing after time reversal. © 2007 Optical Society of America.
Motsclés: Diffraction; Electromagnetic waves; Frequency domain analysis; Green's function; Microcavities; Time reversal cavity; Electromagnetic fields


Interaction of a surface wave with a dislocation Maurel, A., V. Pagneux, F. Barra, and F. Lund Physical Review B  Condensed Matter and Materials Physics 75, no. 22 (2007)
Résumé: The scattering of a surface wave by a pinned edge dislocation in a semiinfinite, homogeneous, isotropic, threedimensional elastic solid is investigated analytically and numerically. An incident wave excites the dislocation that responds by oscillating as a string endowed with mass, line tension, and damping. The oscillations of the stringlike dislocation generate secondary ("scattered") elastic waves that are the primary object of interest in this study. The back reaction of the reemitted waves on the dislocation dynamics is neglected, but the wavelength of the radiation is allowed to be large, comparable, or small compared to the length of the dislocation. In view of recent experimental visualizations of these phenomena, we focus particularly on the field behavior at the free surface near the dislocation, and not just on the far field. For the same reason, it is the vertical component of displacement at the free surface that is studied in detail. An efficient numerical procedure for the computation of the appropriate components of the Green's function, using a Filon quadrature for the integration of rapidly oscillating functions, is developed. The numerics is validated with known analytical expressions. The secondary radiation generated by the response of the dislocation to the incident wave is also calculated numerically, and the results are also validated by comparing them with the analytical expressions that can be obtained when the radiation wavelength is very long compared to dislocation length. The interference pattern between incident wave and secondary wave that is generated at the free surface is studied in detail and found to depend strongly not only on wavelength and dislocation geometry (length and orientation) but also on dislocation depth, with the response of the dislocation being a particularly sensitive function of such depth. Results are compared with recent experiments of Shilo and Zolotoyabko [Phys. Rev. Lett. 91, 115506 (2003)] that report visualizations of the surfacewavedislocation interaction using stroboscopic xray imaging. A satisfactory agreement is found. Dislocation velocities of a few percent of the speed of sound and viscosity coefficients of about 105 Pa s are inferred. © 2007 The American Physical Society.


Multiple scattering from assemblies of dislocation walls in three dimensions. Application to propagation in polycrystals Maurel, A., V. Pagneux, F. Barra, and F. Lund Journal of the Acoustical Society of America 121, no. 6, 34183431 (2007)
Résumé: The attenuation of ultrasound in polycrystalline materials is modeled with grain boundaries considered as arrays of dislocation segments, a model valid for low angle mismatches. The polycrystal is thus studied as a continuous medium containing many dislocation "walls" of finite size randomly placed and oriented. Wave attenuation is blamed on the scattering by such objects, an effect that is studied using a multiple scattering formalism. This scattering also renormalizes the speed of sound, an effect that is also calculated. At low frequencies, meaning wavelengths that are long compared to grain boundary size, then attenuation is found to scale with frequency following a law that is a linear combination of quadratic and quartic terms, in agreement with the results of recent experiments performed in copper [Zhang, J. Acoust. Soc. Am. 116(1), 109116 (2004)]. The prefactor of the quartic term can be obtained with reasonable values for the material under study, without adjustable parameters. The prefactor of the quadratic term can be fit assuming that the drag on the dynamics of the dislocations making up the wall is one to two orders of magnitude smaller than the value usually accepted for isolated dislocations. The quartic contribution is compared with the effect of the changes in the elastic constants from grain to grain that is usually considered as the source of attenuation in polycrystals. A complete model should include this scattering as well. © 2007 Acoustical Society of America.
Motsclés: Dislocations (crystals); Elastic constants; Grain boundaries; Grain size and shape; Multiple scattering; Three dimensional; Wavelength; Dislocation walls; Grain boundary size; Isolated dislocations; Low angle mismatches; Polycrystals; article; crystal; dynamics; materials testing; mathematical analysis; model; priority journal; sound transmission; ultrasound; waveform; Crystallization; Elasticity; Mathematics; Models, Theoretical; Scattering, Radiation; Sound; Viscosity


Lamb wave propagation in elastic waveguides with variable thickness Pagneux, V., and A. Maurel Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 462, no. 2068, 13151339 (2006)
Résumé: The problem of Lamb wave propagation in waveguides with varying height is treated by a multimodal approach. The technique is based on a rearrangement of the equations of elasticity that provides a new system of coupled mode equations preserving energy conservation. These coupled mode equations avoid the usual problem at the cutoffs with zero wavenumber. Thereafter, we define an impedance matrix that is governed by a Riccati equation yielding a stable numerical computation of the solution. Incidentally, the versatility of the multimodal method is exemplified by treating analytically the case of slowly varying guide and by showing how to get easily the Green tensor in any geometry. The method is applied for a waveguide whose height is described by a Gaussian function and the energy conservation in verified numerically. We determine the Green tensor in this geometry. © 2006 The Royal Society.
Motsclés: Elastic waveguide; Impedance matrix; Lamb modes; Multimodal method; Scattering; Varying height


Thermal radiation scanning tunnelling microscopy De Wilde, Y., F. Formanek, R. Carminati, B. Gralak, P.A. Lemoine, K. Joulain, J.P. Mulet, Y. Chen, and J.J. Greffet Nature 444, no. 7120, 740743 (2006)
Résumé: In standard nearfield scanning optical microscopy (NSOM), a subwavelength probe acts as an optical 'stethoscope' to map the near field produced at the sample surface by external illumination. This technique has been applied using visible, infrared, terahertz and gigahertz radiation to illuminate the sample, providing a resolution well beyond the diffraction limit. NSOM is well suited to study surface waves such as surface plasmons or surfacephonon polaritons. Using an aperture NSOM with visible laser illumination, a nearfield interference pattern around a corral structure has been observed, whose features were similar to the scanning tunnelling microscope image of the electronic waves in a quantum corral. Here we describe an infrared NSOM that operates without any external illumination: it is a nearfield analogue of a nightvision camera, making use of the thermal infrared evanescent fields emitted by the surface, and behaves as an optical scanning tunnelling microscope. We therefore term this instrument a 'thermal radiation scanning tunnelling microscope' (TRSTM). We show the first TRSTM images of thermally excited surface plasmons, and demonstrate spatial coherence effects in nearfield thermal emission. ©2006 Nature Publishing Group.
Motsclés: diffraction; scanning tunnelling microscopy; temperature effect; article; illumination; infrared radiation; microscope; near field scanning optical microscopy; priority journal; radiation; scanning tunneling microscopy; signal detection; surface plasmon resonance; thermal radiation scanning tunneling microscopy


Propagation of elastic waves through polycrystals: The effects of scattering from dislocation arrays Maurel, A., V. Pagneux, D. Boyer, and F. Lund Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 462, no. 2073, 26072623 (2006)
Résumé: We address the problem of an elastic wave coherently propagating through a twodimensional polycrystal. The main source of scattering is taken to be the interaction with grain boundaries that are in turn modelled as line distribution of dislocationsa good approximation for low angle grain boundaries. First, the scattering due to a single linear array is worked out in detail in a Born approximation, both for longitudinal and transverse polarization and allowing for mode conversion. Next, the polycrystal is modelled as a continuum medium filled with such lines that are in turn assumed to be randomly distributed. The properties of the coherent wave are worked out in a multiple scattering formalism, with the calculation of a mass operator, the main technical ingredient. Expansion of this operator to secondorder in perturbation theory gives expressions for the index of refraction and attenuation length. This work is motivated by two sources of recent experiments: firstly, the experiments of Zhang et al. (Zhang, G., Simpson Jr, W. A., Vitek, J. M., Barnard, D. J., Tweed, L. J. & Foley J. 2004 J. Acoust. Soc. Am. 116, 109116.) suggesting that current understanding of wave propagation in polycrystalline material fails to interpret experimental results; secondly, the experiments of Zolotoyabko & Shilo who show that dislocations are potentially strong scatterers for elastic waves. © 2006 The Royal Society.
Motsclés: Dislocations; Effective medium; Grain boundary; Multiple scattering; Polycrystal; Scattering function


Characterization of an experimental turbulent vortex in the physical and spectral spaces Cuypers, Y., A. Maurel, and P. Petitjeans Journal of Turbulence 7, 113 (2006)
Résumé: We present an experiment where a stretched vortex is experiencing quasiperiodical turbulent bursts inside a laminar environment. In previous studies (Cuypers et al., 2003 Phys. Rev. Lett., 91, 194502, Cuypers et al., 2004 J. Turb., 5), the classical k5/3 decay of the spectrum resulting from the evolution of this burst has been characterized and interpreted in the framework of Lundgren's mechanism (Lundgren 1982 Phys. Fluids 25 2193). In this paper, the flow is further characterized in both the physical and the spectral spaces using a statistical exploitation of phase averaged particle image velocimetry measurements. © 2006 Taylor & Francis.
Motsclés: Flow measurement; Laminar flow; Spectrum analysis; Statistical methods; Turbulent flow; Velocity measurement; Vortex flow; turbulence; vortex


Wave propagation through a random array of pinned dislocations: Velocity change and attenuation in a generalized Granato and Lücke theory Maurel, A., V. Pagneux, F. Barra, and F. Lund Physical Review B  Condensed Matter and Materials Physics 72, no. 17 (2005)
Résumé: A quantitative theory of the elastic wave damping and velocity change due to interaction with dislocations is presented. It provides a firm theoretical basis and a generalization of the Granato and Lücke model [J. Appl. Phys. 27, 583 (1956)]. This is done considering the interaction of transverse (T) and longitudinal (L) elastic waves with an ensemble of dislocation segments randomly placed and randomly oriented in an elastic solid. In order to characterize the coherent wave propagation using multiple scattering theory, a perturbation approach is used, which is based on a wave equation that takes into account the dislocation motion when forced by an external stress. In our calculations, the effective velocities of the coherent waves appear at first order in perturbation theory while the attenuations have a part at first order due to the internal viscosity and a part at second order due to the energy that is taken away from the incident direction. This leads to a frequency dependence law for longitudinal and transverse attenuations that is a combination of quadratic and quartic terms instead of the usual quadratic term alone. Comparison with resonant ultrasound spectroscopy (RUS) and electromagnetic acoustic resonance (EMAR) experiments is proposed. The present theory explains the difference experimentally observed between longitudinal and transverse attenuations [Ledbetter, J. Mater. Res. 10, 1352 (1995)]. © 2005 The American Physical Society.


Interaction between an elastic wave and a single pinned dislocation Maurel, A., V. Pagneux, F. Barra, and F. Lund Physical Review B  Condensed Matter and Materials Physics 72, no. 17 (2005)
Résumé: Acoustic, and more generally elastic, waves in solids are damped by several mechanisms, among which dislocation motion is believed to play an important role. This is because an elastic wave interacts with a dislocation causing it to oscillate in response, and the resulting transfer of energy from wave to dislocation damps the acoustic vibrations. Recently, improved experimental techniques as well as improved numerical methods have been able to probe in some detail this interaction, isolating the effect of a single dislocation, and at this stage the theory, in its analytic form, is not sufficiently developed to provide quantitative comparison with experimental data and computer simulations. There is thus a need for an improved theoretical study of this issue. In this paper, we consider the interaction of transverse (T) and longitudinal (L) polarized waves in a homogeneous and isotropic, three dimensional, continuum linear elastic medium interacting with a dislocation segment pinned at both ends. An elastic wave incident upon such a dislocation segment is scattered, and the resulting scattered wave is characterized by its scattering amplitudes, that account for possible TL mode conversions. Such scattering amplitudes are explicitly calculated. As a consequence, it is possible to calculate the resulting interference patterns of incident with scattered wave, such as have been observed in recent experiments [Shilo and Zolotoyabko, Phys. Rev. Lett. 91, 115506 (2003)]. The energy loss per cycle is also calculated using the optical theorem and results are shown to be in qualitative agreement with the results of numerical experiments [Greaney, Comput. Mater. Sci. 25, 387 (2002)]. © 2005 The American Physical Society.


Modal representation of spatial coherence in dissipative and resonant photonic systems Sauvan, C., J. P. Hugonin, R. Carminati, and P. Lalanne Physical Review A 89, no. 4 (2014)


Propagation in waveguides with varying cross section and curvature: a new light on the role of supplementary modes in multimodal methods Maurel, A., J.F. Mercier, and S. Felix Proceedings Of The Royal Society AMathematical Physical And Engineering Sciences 470, no. 2166 (2014)
Motsclés: waveguide; multimodal method; boundary mode; admittance matrix


Elastic wave propagation through a distribution of dislocations Maurel, A., V. Pagneux, D. Boyer, and F. Lund Materials Science and Engineering A 400401, no. 12 SUPPL., 222225 (2005)
Résumé: We study the coherent propagation of an elastic wave in a twodimensional continuous elastic medium filled with dislocation arrays randomly distributed and oriented in space. This configuration reasonably mimics grain boundaries in polycrystals. Interest is in evaluating the plastic contributions to the multiple scattering of waves in polycrystals that may superpose to other known scattering processes, like scattering due to inhomogeneities of elastic properties among grains. Calculations are performed in a multiple scattering formalism, based on the derivation of the socalled mass operator, in the approximation of weak scattering. We find that sound attenuation increases when the frequency decreases, a trend opposite to the usual behavior, suggesting that dislocations could sensibly modify the acoustic properties of materials at low frequency. © 2005 Elsevier B.V. All rights reserved.
Motsclés: Dislocations; Grain boundary; Multiple scattering; Polycrystal; Acoustic properties; Approximation theory; Grain boundaries; Polycrystals; Scattering; Wave propagation; Coherent propagation; Dislocations arrays; Mass operator; Sound attentuation; Elastic waves; wave propagation


Comparison between an experimental turbulent vortex and the Lundgren vortex Cuypers, Y., A. Maurel, and P. Petitjeans Journal of Turbulence 5 (2004)
Résumé: In a recent letter (Cuypers Y et al 2003 Phys. Rev. Lett. 91 194502), the authors presented experimental results on a structure resulting from a vortex burst. The temporal evolution of this structure results in the k5/3 Kolmogorov spectrum and some common features with the Lundgren theoretical vortex have been shown. The purpose of the present paper is to go further in the comparison with the Lundgren model by a parallel analysis of the experimental structure and of a Lundgren single spiral vortex, whose evolution is numerically obtained based on the calculations of Pullin et al (1993 Phys. Fluids A 5 126; 1994 Phys. Fluids 6 3010). ©2004 IOP Publishing Ltd.
Motsclés: mathematical modeling; turbulence; vortex


Vortex burst as a source of turbulence Cuypers, Y., A. Maurel, and P. Petitjeans Physical Review Letters 91, no. 19, 194502/1194502/4 (2003)
Résumé: The vortex burst in a laminarflow environment was shown to be responsible for the build up of the energy cascade. It was believed to be the first time that a single isolated flow structure was identified to produce the part of the turbulent energy spectrum described by Kolmogorov's k5/3 law. In addition, this structure seems to have some common feature with the theoretical one of Lundgren.
Motsclés: Imaging techniques; Laminar flow; Mathematical models; Numerical methods; Turbulence; Turbulent flow; Velocity measurement; Energy spectrum; Flow structure; Particle imaging velocimetry; Vortex flow


Instability of a confined jet impinging on a water/air free surface Bouchet, E., G. Climent, and A. Maurel Europhysics Letters 59, no. 6, 827833 (2002)
Résumé: Selfsustained oscillations in sinuous mode occur when a water jet impinges from below on a water/air free surface. Confined jet instability is experimentally investigated by image processing and velocity measurements. Despite small deformations of the surface, dynamic response of the jet provides unusual behaviour with comparable configurations (holetone, jet edge ⋯). The central feature is a bounded evolution of the oscillation frequency. Modal transitions are observed when physical parameters are varied. Each frequency jump is related to wavelength modification of the spatial pattern. Atypical evolution of the predominant length scale has to be connected to strong coupling with the weak deformations induced by the impinging jet on the free surface.


Determination of Lamb mode eigenvalues Pagneux, V., and A. Maurel Journal of the Acoustical Society of America 110, no. 3 I, 13071314 (2001)
Résumé: An original method is presented to determine the complex Lamb wave spectrum by using a numerical spectral method applied to the elasticity equations. This method presents the advantage to directly determine complex wave numbers for a given frequency via a classical matricial eigenvalue problem, and allows the wave numbers to be determined at relatively high frequencies (i.e., corresponding to many propagating modes). It does not need initial guess values for the wave numbers, contrary to the usual method of root finding of the RayleighLamb frequency equations (dispersion relation) in the complex plane. Results are presented and the method is discussed. © 2001 Acoustical Society of America.
Motsclés: Acoustic wave propagation; Eigenvalues and eigenfunctions; Elasticity; Spectrum analysis; Wave numbers; Acoustics; eigenvalue; wave; analytic method; article; dispersion; elasticity; frequency modulation; mathematical analysis; mathematical computing; priority journal; sound; spectral sensitivity; waveform


Characterization of a large vortex using acoustic timereversal mirrors Manneville, S., A. Maurel, P. Roux, and M. Fink European Physical Journal B 9, no. 3, 545549 (1999)
Résumé: We report new results on the ultrasonic characterization of a fluid flow using an acoustic timereversal mirror (TRM). The structure of a large vortex generated by a rotating disk in a hollow cylinder is investigated both inside and below the cylinder. For meanflow characterization, the TRM is shown to be a powerful vorticity detector. Experimental timeofflight data are successfully compared to a numerical simulation of the flow and the orthoradial velocity is reconstructed using simple geometrical acoustics. Realtime measurements allow us to extract the precession motion of the vortex, providing direct, nonintrusive, and dynamical information on the flow.
Motsclés: 43.30+m underwater sound; 43.35+d ultrasonics, quantum acoustics, and physical effects of sound; 47.32y rotational flow and vorticity


Experimental study of a submerged fountain Maurel, A., S. Cremer, and P. Jenffer Europhysics Letters 39, no. 5, 503508 (1997)
Résumé: We present an experimental study of a vertical planar water jet impinging from below on a water/air interface. Varying the jet velocity and the cavity depth, three regimes are observed: at small velocities or high cavity depths, the jet is stable and the surface bump vertically above the jet is stationary. Increasing the velocity, the bump starts oscillating along the free surface at a welldefined frequency. This motion corresponds to the destabilization of the jet confined in the bulk of the cavity to a selfsustained oscillation regime, characteristic of the behavior of confined jets. Increasing further the velocity induces a transition to a behavior with more complex frequency spectrum. This paper presents a detailed study of the selfsustained oscillation regime. The frequency at the onset is studied as a function of the cavity depth and we show an unusual behavior of the frequency with the distance from the threshold.

