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 (2017): 1423–1432.
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 (2016): 763–767.


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).


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 (2015): 189–193.
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


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 (2014): 17765–17770.
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 (2015): 1–41.
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


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 (2014): 013842.
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 (2013): 11536–11545.
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


Dressed polarizability and absorption of a dipole nanoantenna in an arbitrary environment. Castanié, E., R. Vincent, R. Pierrat, and R. Carminati. In AIP Conference Proceedings, 116–118. Vol. 1475., 2012.
Résumé: In this work, we show how the absporption crosssection of a dipole nanoantenna is modified by the local environment. In particular, we clarify the key role of the Local Density of States (LDOS) and show the analogy that exists with quantum emitters. This link with the LDOS shows that it is possible to probe the LDOS inside a structured environment with a nanoparticle. Conversely, we can design nanostructures to control the level of absorption in a nanoparticle, a strong limitation for applications in nanophotonics. The theoretical results are illustrated numerically in the simple case of a silver particle near a perfect mirror. © 2012 American Institute of Physics.
MotsClés: absorption; local density of states; nanoantenna


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 (2012): 339–344.
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 (2012): 3006–3008.
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.


Enhanced lightmatter interaction at the nanoscale using localized plasmon modes on disordered metallic films. Carminati, R., E. Castanié, V. Krachmalnicoff, A. Cazé, R. Pierrat, and Y. De Wilde. In 2011 Conference on Lasers and ElectroOptics Europe and 12th European Quantum Electronics Conference, CLEO EUROPE/EQEC 2011., 2011.
Résumé: Disordered semicontinuous metallic films are a particularly striking example of complex photonic systems. They exhibit peculiar optical properties that cannot be explained from the behavior of bulk metals or ensembles of isolated nanoparticles [1]. The interplay between surfaceplasmon excitations and scattering by multiscale (fractal) metallic clusters leads to spatial localization of the electromagnetic field in subwavelength areas (hot spots). A feature of these hotspots modes is the expected coexistence of both localized and delocalized modes at the same frequency [2,3], a situation referred to as inhomogeneous localization. © 2011 IEEE.
MotsClés: Bulk metals; Hot spot; Hotspots; Lightmatter interactions; Metallic clusters; Multiscales; Nano scale; Photonic systems; Plasmon modes; Semicontinuous; Spatial localization; Subwavelength; Surface plasmon excitation; Electromagnetic fields; Electron optics; Metallic films; Optical properties; Optics; Quantum electronics; Plasmons


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 fluctuations of the local density of states in a strongly scattering environment. Pierrat, R., A. Cazé, and R. Carminati. In AIP Conference Proceedings, 85–87. Vol. 1291., 2010.
Résumé: We study the local density of states (LDOS) statistics near a dipole emitter embedded in a strongly scattering medium. We perform numerical simulations that emphasize the fact that LDOS fluctuations are strongly affected by the local environment of the emitter and is very sensitive to nearfield interactions and correlation of disorder. © 2010 American Institute of Physics.
MotsClés: Local density of states; Nearfield; Strongly scattering medium


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


Theory of the time reversal cavity for electromagnetic fields. Carminati, R., R. Pierrat, J. De Rosny, and M. Fink. Optics Letters 32, no. 21 (2007): 3107–3109.
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

