Recovering particle velocity and size distributions in ejecta with photon Doppler velocimetry Don Jayamanne, J. A., R. Outerovitch, F. Ballanger, J. Bénier, E. Blanco, C. Chauvin, P. Hereil, J. Tailleur, O. Durand, R. Pierrat, R. Carminati, A. Hervouët, P. Gandeboeuf, and J. R. Burie Journal of Applied Physics 136, no. 8 (2024)
Résumé: When a solid metal is struck, its free surface can eject fast and fine particles. Despite the many diagnostics that have been implemented to measure the mass, size, velocity, or temperature of ejecta, these efforts provide only a partial picture of this phenomenon. Ejecta characterization, especially in constrained geometries, is an inherently illposed problem. In this context, Photon Doppler Velocimetry (PDV) has been a valuable diagnostic, measuring reliably particles and free surface velocities in the single scattering regime. Here, we present ejecta experiments in gas and how, in this context, PDV allows one to retrieve additional information on the ejecta, i.e., information on the particles’ size. We explain what governs ejecta transport in gas and how it can be simulated. To account for the multiple scattering of light in these ejecta, we use the Radiative Transfer Equation (RTE) that quantitatively describes PDV spectrograms, and their dependence not only on the velocity but also on the size distribution of the ejecta. We remind how spectrograms can be simulated by solving numerically this RTE and we show how to do so on hydrodynamic ejecta simulation results. Finally, we use this complex machinery in different ejecta transport scenarios to simulate the corresponding spectrograms. Comparing these to experimental results, we iteratively constrain the ejecta description at an unprecedented level. This work demonstrates our ability to recover particle size information from what is initially a velocity diagnostic, but more importantly it shows how, using existing simulation of ejecta, we capture through simulation the complexity of experimental spectrograms.


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.


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.


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)


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.


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.


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.


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.


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.


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)


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)


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.


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.


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.


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.


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.


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.


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


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.


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)


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


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.


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.


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)


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


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


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


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.


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)


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.


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.


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


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


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


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.


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


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


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

