Optical coherent detection through multiscattering media by wavemixing cleaning effect in liquidcrystal OASLM Bortolozzo, U., S. Residori, F. Ramaz, and J. P. Huignard Optics Letters 48, no. 15, 39693972 (2023)
Résumé: Liquidcrystal (LC) optically addressable spatial light modulators (OASLMs) allow control of the phase and amplitude of optical beams. By performing wave mixing in an OASLM, we show that coherent phase detection can be achieved for light beams passing through highly scattering media, such as foam layers with several cm thicknesses. Thanks to the adaptive response of our OASLM, the phase information on the speckle signal is transferred at the output of the OASLM to the plane wave reference beam, allowing the cleaning of optical distortions and the direct measurement of amplitude phase modulations with a small diameter single photodiode. A good signaltonoise ratio (SNR) is demonstrated for foam thickness up to 3 cm. These properties, together with the recently demonstrated subms response time of our OASLM, make the method compatible with foreseen applications for imaging in biomedical tissues and turbid media.


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.


Dynamic fullfield optical coherence tomography for livecell imaging and growthphase monitoring in Aspergillus fumigatus Maldiney, T., D. GarciaHermoso, E. Sitterlé, J.M. Chassot, O. Thouvenin, C. Boccara, M. Blot, L. Piroth, J.P. Quenot, P.E. Charles, V. Aimanianda, B. Podac, L. Boulnois, F. Dalle, M. Sautour, M.E. Bougnoux, and F. Lanternier Frontiers in Cellular and Infection Microbiology 13 (2023)
Résumé: The diagnosis of cutaneous manifestations of deep mycoses relies on both histopathological and direct examinations. Yet, the current diagnostic criteria cannot prevent missed cases, including invasive aspergillosis, which requires the development of a novel diagnostic approach and imaging tools. We recently introduced the use of dynamic fullfield optical coherence tomography (DFFOCT) in fungal diagnostics with a definition approaching that of conventional microscopy and the ability to return metabolic information regarding different fungal species. The present work focuses on subcellular dynamics and livecell imaging of Aspergillus fumigatus with DFFOCT to follow the fungal growth stages
Motsclés: Aspergillus fumigatus; dynamic fullfield optical coherence tomography; fungal metabolism; invasive fungal infections; livecell imaging


Abnormalities in the retinal capillary plexuses in coasts disease in adulthood on optical coherence tomography angiography Krivosic, V., P. Mecê, C. Dulière, C. Lavia, S. Zegrari, R. Tadayoni, and A. Gaudric Retina (Philadelphia, Pa.) 43, no. 9, 15141524 (2023)
Résumé: PURPOSE: To describe and quantify the abnormalities of the retinal capillary plexuses using optical coherence tomography angiography in Coats disease. METHODS: Retrospective study. Eleven eyes of 11 patients with Coats disease (9 men and two women aged 3280 years) compared with nine fellow eyes and 11 healthy control eyes. Horizontal bands of contiguous 3 × 3 mm optical coherence tomography angiograms of the superficial vascular plexus and deep capillary complex were acquired from the optic disk to 6 mm temporal to the fovea, through areas with telangiectasia visible on fluorescein angiography in 9 cases. RESULTS: The vascular density was significantly decreased in both plexuses in eyes with Coats disease compared with normal and fellow eyes within the 6 mm temporal to the fovea (superficial vascular plexus: 21.5 vs. 29.4%, P = 0.00004 and vs. 30.3%, P = 0.00008; deep capillary complex, 16.5 vs. 23.9%, P = 0.00004 and vs. 24.7%, P = 0.00008, respectively). The fractal dimension was also significantly decreased in eyes with Coats disease (superficial vascular plexus: 1.796 vs. 1.848 P = 0.001 and vs. 1.833, P = 0.003; deep capillary complex: 1.762 vs. 1.853, P = 0.003 and vs. 1.838, P = 0.004, respectively). CONCLUSION: Retinal plexuses' vascular density was decreased in Coats disease, including in areas with no visible telangiectasia.


Realtime detection of virus antibody interaction by labelfree commonpath interferometry Alhaddad, S., H. Bey, O. Thouvenin, P. Boulanger, C. Boccara, M. Boccara, and I. Izeddin Biophysical Reports 3, no. 3, 100119 (2023)
Résumé: Viruses have a profound influence on all forms of life, motivating the development of rapid and minimally invasive methods for virus detection. In this study, we present a novel methodology that enables quantitative measurement of the interaction between individual biotic nanoparticles and antibodies in solution. Our approach employs a labelfree, fullfield commonpath interferometric technique to detect and track biotic nanoparticles and their interactions with antibodies. It is based on the interferometric detection of light scattered by viruses in aqueous samples for the detection of individual viruses. We employ singleparticle tracking analysis to characterize the size and properties of the detected nanoparticles, and to monitor the changes in their diffusive mobility resulting from interactions. To validate the sensitivity of our detection approach, we distinguish between particles having identical diffusion coefficients but different scattering signals, using DNAloaded and DNAdevoid capsids of the Escherichia coli T5 virus phage. In addition, we have been able to monitor, in real time, the interaction between the bacteriophage T5 and purified antibodies targeting its major capsid protein pb8, as well as between the phage SPP1 and nonpurified antiSPP1 antibodies present in rabbit serum. Interestingly, these virusantibody interactions are observed within minutes. Finally, by estimating the number of viral particles interacting with antibodies at different concentrations, we successfully quantify the dissociation constant Kd of the virusantibody reaction using singleparticle tracking analysis.


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.


Comparative analysis of fullfield OCT and optical transmission tomography Alhaddad, S., O. Thouvenin, M. Boccara, C. Boccara, and V. Mazlin Biomedical Optics Express 14, no. 9, 48454861 (2023)
Résumé: This work compares two tomographic imaging technologies, timedomain fullfield optical coherence tomography (FFOCT) working in reflection and optical transmission tomography (OTT), using a new optical setup that combines both. We show that, due to forwardscattering properties, the axial sectioning and contrast in OTT can be optimized by tuning illumination. The influence of sample scattering and thickness are discussed. We illustrate the comparison of the two methods in static (morphology) and dynamic (metabolic contrast) regimes using cell cultures, tissues and entire organisms emphasizing the advantages of both approaches.


StickSlip Nucleation and Failure in Uniform Glass Beads Detected by Acoustic Emissions in RingShear Experiments: Implications for Identifying the Acoustic Emissions of Earthquake Foreshocks Gou, H. X., W. Hu, Q. Xu, R. Q. Huang, M. J. Mcsaveney, X. Jia, and Y. J. Wang Journal of Geophysical Research: Solid Earth 128, no. 8 (2023)
Résumé: Stress accumulation and release reflected by acoustic emissions (AEs) during shearing of granular materials provide important information on failure mechanisms in seismic faults and landslides controlled by stickslip. Among many characteristics (amplitude, energy, counts, and frequency) of AE signals generated by stickslip, stress changes corresponding to various frequency AEs in different stages of the stickslip process are not clear, which limits our knowledge of the characteristics of precursory signals before stickslip failure. To better understand the physical mechanisms of granular stickslip, we monitored the mechanical and AE signals using highfrequency (2 MHz) synchronous acquisition during constantspeed shear of packs of uniform glass beads with different sizes at different normal stresses. The release rate of AE energy was found to accelerate with the dilatation of the sample volume, and the stress drop of stickslip was augmented with the increase of normal stress and particle size. Three characteristic events of single cycle stickslip were observed in this study: main slip, minor slip, and microslip. We analyzed the AE frequency spectra of these three event types. Both main slip and minor slip corresponded to stress drop and generated highfrequency AEs (about several hundred kHz), while the AE frequencies generated by microslip were lower (about tens of kHz) and exhibited stress strengthening, which were not apparent in previous studies due to the low frequency of acquisition. We propose that the microslip is mainly due to sliding on grain contacts, while the main slip and minor slip resulted from breakage and reforming of force chains. Lowfrequency AEs from microslip may suggest a crucial precursor of seismic faults and landslides.


Interface selfreferenced dynamic fullfield optical coherence tomography Monfort, T., S. Azzollini, T. B. Yacoub, I. Audo, S. Reichman, K. Grieve, and O. Thouvenin Biomedical Optics Express 14, no. 7, 34913505 (2023)
Résumé: Dynamic fullfield optical coherence tomography (DFFOCT) has recently emerged as an invaluable live labelfree and noninvasive imaging modality able to image subcellular biological structures and their metabolic activity within complex 3D samples. However, DFFOCT suffers from fringe artefacts when imaging near reflective surfaces and is highly sensitive to vibrations. Here, we present interface SelfReferenced (iSR) DFFOCT, an alternative configuration to DFFOCT that takes advantage of the presence of the sample coverslip in between the sample and the objective by using it as a defocused reference arm, thus avoiding the aforementioned artefacts. We demonstrate the ability of iSR DFFOCT to image 2D fibroblast cell cultures, which are among the flattest mammalian cells.


Notes on osculations and mode tracing in semianalytical waveguide modeling Gravenkamp, H., B. Plestenjak, and D. A. Kiefer Ultrasonics 135, 107112 (2023)
Résumé: The dispersion curves of (elastic) waveguides frequently exhibit crossings and osculations (also known as veering, repulsion, or avoided crossing). Osculations are regions in the dispersion diagram where curves approach each other arbitrarily closely without ever crossing before veering apart. In semianalytical (undamped) waveguide models, dispersion curves are obtained as solutions to discretized parameterized Hermitian eigenvalue problems. In the mathematical literature, it is known that such eigencurves can exhibit crossing points only if the corresponding matrix flow (parameterdependent matrix) is uniformly decomposable. We discuss the implications for the solution of the waveguide problem. In particular, we make use of a simple algorithm recently suggested in the literature for decomposing matrix flows. We also employ a method for mode tracing based on approximating the eigenvalue problem for individual modes by an ordinary differential equation that can be solved by standard procedures.


Full control of electric and magnetic lightmatter interactions through a nanomirror on a nearfield tip Reynier, B., E. Charron, O. Markovic, X. Yang, B. Gallas, A. Ferrier, S. Bidault, and M. Mivelle Optica 10, no. 7, 841845 (2023)
Résumé: Lightmatter interactions are often considered governed by the electric optical field only, leaving aside the magnetic component of light. However, the magnetic part plays a determining role in many optical processes, from light and chiralmatter interactions and photonavalanching to forbidden photochemistry, making the manipulation of magnetic processes extremely relevant. Here, by creating a standing wave using a metallic nanomirror, we manipulate the spatial distributions of electric and magnetic fields and their associated local densities of states, allowing selective control of the excitation and emission of electric and magnetic dipolar transitions. This control allows us to image, in 3D, the electric and magnetic nodes and antinodes of the fields' interference patterns. It also enables us to enhance specifically photoluminescence from quantum emitters excited only by the magnetic field, and to manipulate their spontaneous emission by acting on the excitation fields solely, demonstrating full control of magnetic and electric lightmatter interactions.


Dynamic optical coherence tomography for cell analysis [Invited] Azzollini, S., T. Monfort, O. Thouvenin, and K. Grieve Biomedical Optics Express 14, no. 7, 33623379 (2023)
Résumé: Labelfree live optical imaging of dynamic cellular and subcellular features has been made possible in recent years thanks to the advances made in optical imaging techniques, including dynamic optical coherence tomography (DOCT) methods. These techniques analyze the temporal fluctuations of an optical signal associated with the active movements of intracellular organelles to obtain an ensemble metric recapitulating the motility and metabolic state of cells. They hence enable visualization of cells within compact, static environments and evaluate their physiology. These emerging microscopies show promise, in particular for the threedimensional evaluation of live tissue samples such as freshly excised biopsies and 3D cell cultures. In this review, we compare the various techniques used for dynamic OCT. We give an overview of the range of applications currently being explored and discuss the future outlook and opportunities for the field.


Tools for GroundTruthFree Passive Client Density Mapping in MACRandomized Outdoor WiFi Networks Yang, F., I. Ahriz, and B. Denby Sensors (Basel, Switzerland) 23, no. 13, 6142 (2023)
Résumé: In the past few years, data privacy legislation has hampered the ability of WiFi network operators to count and map client activity for commercial and security purposes. Indeed, since client device MAC devices are now randomized at each transmission, aggregating client activity using management frames such as Probe Requests, as has been common practice in the past, becomes problematic. Recently, researchers have demonstrated that, statistically, client counts are roughly proportional to raw Probe Request counts, thus somewhat alleviating the client counting problem, even if, in most cases, ground truth measurements from alternate sensors such as cameras are necessary to establish this proportionality. Nevertheless, localizing randomized MAC clients at a network site is currently an unsolved problem. In this work, we propose a set of nine tools for extending the proportionality between client counts and Probe Requests to the mapping of client densities in realworld outdoor WiFi networks without the need for ground truth measurements. The purpose of the proposed toolkit is to transform raw, randomized MAC Probe Request counts into a density map calibrated to an estimated number of clients at each position.


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.


Suppression of the Talbot effect in Fourier transform acoustooptic imaging Bocoum, M., F. Figliolia, J. P. Huignard, F. Ramaz, and J. M. Tualle Applied Optics 62, no. 18, 47404746 (2023)
Résumé: We report on the observation and correction of an imaging artifact attributed to the Talbot effect in the context of acoustooptic imaging using structured acoustic waves. When ultrasound waves are emitted with a periodic structure, the Talbot effect produces πphase shifts of that periodic structure at every half of the Talbot distance in propagation. This unwanted artifact is detrimental to the image reconstruction, which assumes nearfield diffraction is negligible. Here, we demonstrate both theoretically and experimentally how imposing an additional phase modulation on the acoustic periodic structure induces a symmetry constraint leading to the annihilation of the Talbot effect. This will significantly improve the acoustooptic image reconstruction quality and allows for an improvement of the reachable spatial resolution of the image.


Automatic diagnosis and classification of breast surgical samples with dynamic fullfield OCT and machine learning Scholler, J., D. Mandache, M. C. Mathieu, A. B. Lakhdar, M. Darche, T. Monfort, C. Boccara, J. C. OlivoMarin, K. Grieve, V. MeasYedid, E. B. a. l. Guillaume, and O. Thouvenin Journal of Medical Imaging 10, no. 3 (2023)
Résumé: Purpose: The adoption of emerging imaging technologies in the medical community is often hampered when they provide a new unfamiliar contrast that requires experience to be interpreted. Dynamic fullfield optical coherence tomography (DFFOCT) microscopy is such an emerging technique. It provides fast, highresolution images of excised tissues with a contrast comparable to H&E histology but without any tissue preparation and alteration. Approach: We designed and compared two machine learning approaches to support interpretation of DFFOCT images of breast surgical specimens and thus provide tools to facilitate medical adoption. We conducted a pilot study on 51 breast lumpectomy and mastectomy surgical specimens and more than 1000 individual 1.3 × 1.3 mm2 images and compared with standard H&E histology diagnosis. Results: Using our automatic diagnosis algorithms, we obtained an accuracy above 88% at the image level (1.3 × 1.3 mm2) and above 96% at the specimen level (above cm2). Conclusions: Altogether, these results demonstrate the high potential of DFFOCT coupled to machine learning to provide a rapid, automatic, and accurate histopathology diagnosis with minimal sample alteration.


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.


Timedomain fullfield optical coherence tomography (TDFFOCT) in ophthalmic imaging Zhang, J., V. Mazlin, K. Fei, A. C. Boccara, J. Yuan, and P. Xiao Therapeutic Advances in Chronic Disease 14, 204062232311701 (2023)
Résumé: Ocular imaging plays an irreplaceable role in the evaluation of eye diseases. Developing cellularresolution ophthalmic imaging technique for more accurate and effective diagnosis and pathogenesis analysis of ocular diseases is a hot topic in the crosscutting areas of ophthalmology and imaging. Currently, ocular imaging with traditional optical coherence tomography (OCT) is limited in lateral resolution and thus can hardly resolve cellular structures. Conventional OCT technology obtains ultrahigh resolution at the expense of a certain imaging range and cannot achieve full field of view imaging. In the early years, Timedomain fullfield OCT (TDFFOCT) has been mainly used for ex vivo ophthalmic tissue studies, limited by the low speed and low fullwell capacity of existing twodimensional (2D) cameras. The recent improvements in system design opened new imaging possibilities for in vivo applications thanks to its distinctive optical properties of TDFFOCT such as a spatial resolution almost insensitive to aberrations, and the possibility to control the curvature of the optical slice. This review also attempts to look at the future directions of TDFFOCT evolution, for example, the potential transfer of the functionalimaging dynamic TDFFOCT from the ex vivo into in vivo use and its expected benefit in basic and clinical ophthalmic research. Through noninvasive, widefield, and cellularresolution imaging, TDFFOCT has great potential to be the nextgeneration imaging modality to improve our understanding of human eye physiology and pathology.


Dynamic Cell Imaging: application to the diatom Phaeodactylum tricornutum under environmental stresses Bey, H., F. Charton, H. Cruz De Carvalho, S. Liu, R. G. Dorrell, C. Bowler, C. Boccara, and M. Boccara European Journal of Phycology 58, no. 2, 145155 (2023)
Résumé: The dynamic movement of cell organelles is an important and poorly understood component of cellular organization and metabolism. In this work we present a noninvasive nondestructive method (Dynamic Cell Imaging, DCI) based on light scattering and interferometry to monitor dynamic events within photosynthetic cells using the diatom Phaeodactylum tricornutum as a model system. For this monitoring we acquire for a few seconds movies of the signals that are related to the motion of dynamic structures within the cell (denoted scatterers), followed by a statistical analysis of each pixel time series. Illuminating P. tricornutum with LEDs of different wavelengths associated with short pulsed or continuouswave modes of illumination revealed that dynamic movements depend on chloroplast activity, in agreement with the reduction in the number of pixels with dynamic behaviour after addition of photosystem II inhibitors. We studied P. tricornutum under two environmentally relevant stresses, iron and phosphate deficiency. The major dynamic sites were located within lipid droplets and chloroplast envelope membranes. By comparing standard deviation and cumulative sum analyses of the time series, we showed that within the droplets two types of scatterer movement could be observed: random motion (Brownian type) but also anomalous movements corresponding to a drift which may relate to molecular fluxes within a cell. The method appears to be valuable for studying the effects of various environments on microalgae in the laboratory as well as in natural aquatic environments. HIGHLIGHTS: Light scattering is an alternative to fluorescence to rapidly evidence dynamic processes. Lipid droplets are the major metabolic active sites under stress. A nondestructive visualization method suitable for laboratory microalgae and aquatic samples.


Acoustic Emissions of Nearly Steady and Uniform Granular Flows: A Proxy for Flow Dynamics and Velocity Fluctuations Bachelet, V., A. Mangeney, R. Toussaint, J. De Rosny, M. I. Arran, M. Farin, and C. Hibert Journal of Geophysical Research: Earth Surface 128, no. 4 (2023)
Résumé: The seismic waves emitted during granular flows are generated by different sources: high frequencies by interparticle collisions and low frequencies by global motion and large scale deformation. To unravel these different mechanisms, an experimental study has been performed on the seismic waves emitted by dry, dense, quasisteady granular flows. The emitted seismic waves were recorded using shock accelerometers and the flow dynamics were captured with a fast camera. The mechanical characteristics of the particle collisions were analyzed, along with the intervals between collisions and the correlations in particles' motion. The highfrequency seismic waves (1–50 kHz) were found to originate from particle collisions and waves trapped in the flowing layer. The lowfrequency waves (20–60 Hz) were generated by particles' oscillations along their trajectories, that is, from cycles of dilation/compression during coherent shear. The profiles of granular temperature (i.e., the mean squared value of particle velocity fluctuations) and average velocity were measured and related to each other, then used in a simple steady granular flow model, in which the seismic signal consists of the variously attenuated contributions of shearinduced Hertzian collisions throughout the flow, to predict the rate at which seismic energy was emitted. Agreement with the measured seismic power was reasonable, and scaling laws relating the seismic power, the shear strain rate and the inertial number were derived. In particular, the emitted seismic power was observed to be approximately proportional to the root mean square velocity fluctuation to the power 3.1 ± 0.9, with the latter related to the mean flow velocity.


Damage in cohesive granular materials: simulations and geophysical implications Canel, V., M. Campillo, X. Jia, and I. R. Ionescu Comptes Rendus  Geoscience 355, no. S3, 121 (2023)
Résumé: The aim of this paper is to test a simple damage model of a cohesive granular medium to study the relationship between the damage and velocity of elastic waves. Our numerical experiments of edometric compression show that the microscopic deformation quickly becomes very heterogeneous, while our simulations of elastic waves propagation show that a small amount of damage induces a dramatic decrease in the elastic velocity. This shows that cohesive discrete media are very sensitive to strain field heterogeneity, and that the wave velocities in these media can measure subtle transient deformation processes, such as earthquake initiation phases.


Strainmediated ionion interaction in rareearthdoped solids LouchetChauvet, A., and T. Chanelière Journal of Physics Condensed Matter 35, no. 30, 305501 (2023)
Résumé: It was recently shown that the optical excitation of rareearth ions produces a local change of the host matrix shape, attributed to a change of the rareearth ion's electronic orbital geometry. In this work we investigate the consequences of this piezoorbital backaction and show from a macroscopic model how it yields a disregarded ionion interaction mediated by mechanical strain. This interaction scales as 1/r3, similarly to the other archetypal ionion interactions, namely electric and magnetic dipoledipole interactions. We quantitatively assess and compare the magnitude of these three interactions from the angle of the instantaneous spectral diffusion mechanism, and reexamine the scientific literature in a range of rareearth doped systems in the light of this generally underestimated contribution.


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.


SinglePixel Photoacoustic Microscopy with Speckle Illumination CaravacaAguirre, A. M., F. Poisson, D. Bouchet, N. Stasio, P. Moreau, I. Wang, E. Zhang, P. Beard, C. Prada, C. Moser, D. Psaltis, O. Katz, and E. Bossy Intelligent Computing 2 (2023)
Résumé: Widefield opticalresolution microscopy with structured illumination and singlepixel detection has been the topic of a number of research investigations. Its advantages over point scanning approaches are many and include a faster acquisition rate for sparse samples, sectioning, and superresolution features. Initially introduced for fluorescence imaging, structured illumination approaches have been adapted and developed for many other imaging modalities. In this paper, we illustrate how speckle illumination, as a particular type of structured illumination, can be exploited to perform opticalresolution photoacoustic microscopy with a singlepixel imaging approach. We first introduce the principle of singlepixel detection applied to photoacoustic imaging and then illustrate in 2 different situations how photoacoustic images may be computationally reconstructed from speckle illumination: In the first situation where the speckle patterns are known through a prior calibration, various reconstruction approaches may be implemented, which are demonstrated experimentally through both scattering layers and multimode optical fibers; in the second situation where the speckle patterns are unknown (blind structured illumination), the socalled memory effect can be harnessed to produce calibrationfree photoacoustic images, following the approach initially proposed for fluorescence imaging through thin scattering layers.


Guided elastic waves in a highlystretched soft plate Delory, A., F. Lemoult, A. Eddi, and C. Prada Extreme Mechanics Letters, 102018 (2023)


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)


Exactly solvable model behind BoseHubbard dimers, InceGauss beams, and aberrated optical cavities GutiérrezCuevas, R., O', D. H. J. dell, M. R. Dennis, and M. A. Alonso Physical Review A 107, no. 3 (2023)
Résumé: By studying the effects of quadratic anisotropy and quartic perturbations on twodimensional harmonic oscillators, one arrives at a simple model, termed here the Ince oscillator, whose analytic solutions are given in terms of Ince polynomials. This one model unifies diverse physical systems, including aberrated optical cavities that are shown to support InceGauss beams as their modes, and the twomode BoseHubbard dimer describing two coupled superfluids. The Ince oscillator model describes a topological transition which can have very different origins: in the optical case, which is fundamentally linear, it is driven by the ratio of astigmatic to spherical mirror aberrations, whereas in the superfluid case it is driven by the ratio of particle tunneling to interparticle interactions and corresponds to macroscopic quantum selftrapping.


Maximizing Focus Quality Through Random Media with DiscretePhaseSampling Lenses Wang, Q., M. Fink, and G. Ma Physical Review Applied 19, no. 3 (2023)
Résumé: Wavefronts modulated by a discretephasesampling lens, such as a spatial light modulator or a digital micromirror device, can be brought into focus after propagating through a random medium. Such techniques are a cornerstone for wave manipulations in multiple scattering environments. In this work, we examine prevailing focusing protocols, including matched filtering and inverse filtering, from the perspective of focus quality, which is defined as the contrast between the energy delivered to the focal peak and the total transmitted energy. Our results show that conventional protocols have limitations in achieving the best focus quality. Based on these analyses, we present an improved wavefrontshaping protocol that directly prioritizes focus quality. The influence of phase sampling resolutions is also analyzed in conjunction with these focusing protocols. Our results can merit the future design and implementation of intelligent lenses, which may potentially benefit various disciplines such as energy delivery, imaging, and communication.


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.


Compressive sensingbased correlation sidelobe suppression for passive water pipeline fault detection using ambient noise Li, Z., P. Lee, M. Fink, R. Murch, and M. Davidson Mechanical Systems and Signal Processing 195, 110323 (2023)
Résumé: The ambient noise in water pipelines are observed as spontaneous signal sources that can be used for pipe fault detection by correlation analysis. However, the limited bandwidth of these noise signal causes strong correlation sidelobes, which introduces significant ambiguities when extracting the system response from correlation results and this increases the risk of false alarms from fault detections. This paper proposes a compressive sensing based method that can extend the noise bandwidth and suppress the correlation sidelobes. Numerical and field experiment results have shown that with the recovered wider bandwidth, the correlation sidelobes can be significantly suppressed and the pipe faults can be identified with greater certainty. The impacts of fault size as well as noise bandwidth, strength and spectrum features on the proposed method are also assessed through numerical experiments.


Restoring and tailoring very high dimensional spatial entanglement of a biphoton state transmitted through a scattering medium Devaux, F., A. Mosset, S. M. Popoff, and E. Lantz Journal of Optics 25, no. 5, 055201 (2023)
Résumé: We report experimental results where a momentum entangled biphoton state with a Schmidt number of a few thousand is retrieved and manipulated when only one photon of the pair is transmitted through a thin scattering medium. For this purpose, the transmission matrix of the complex medium is first measured with a phaseshifting interferometry measurement method using a spatial light modulator (SLM) illuminated with a laser source. From this matrix, different phase masks are calculated and addressed on the SLM to spatially control the focusing of the laser through the complex medium. These same masks are used to manipulate the phase of the biphoton wave function transmitted by the thin diffuser in order to restore and control in the same way the momentum correlations between the farfield images of twin beams issued from strongly spatialmultimode spontaneous parametric down conversion.
Motsclés: quantum optics, entenglement, wavefront shaping, scattering media


DampingDriven Time Reversal for Waves HidalgoCaballero, S., S. Kottigegollahalli Sreenivas, V. Bacot, S. Wildeman, M. Harazi, X. Jia, A. Tourin, M. Fink, A. Cassinelli, M. Labousse, and E. Fort Physical Review Letters 130, no. 8 (2023)
Résumé: Damping is usually associated with irreversibility. Here, we present a counterintuitive concept to achieve time reversal of waves propagating in a lossless medium using a transitory dissipation pulse. Applying a sudden and strong damping in a limited time generates a timereversed wave. In the limit of a high damping shock, this amounts to "freezing"the initial wave by maintaining the wave amplitude while canceling its time derivative. The initial wave then splits in two counterpropagating waves with half of its amplitude and time evolutions in opposite directions. We implement this dampingbased time reversal using phonon waves propagating in a lattice of interacting magnets placed on an air cushion. We show with computer simulations that this concept also applies to broadband time reversal in complex disordered systems.


Passive antenna characterization through impedance correlations in a diffuse field Tamart, M., J. De Rosny, and E. Richalot IEEE Transactions on Antennas and Propagation, 11 (2023)
Résumé: Ambient noise correlations allow the passive recovery of Green’s functions between two probes. Recently, the same approach has been applied to electromagnetism, but by correlating diffuse fields in mode stirred chambers. Until now, only correlation of Sparameters has been studied. However, it has very recently been shown that the result can be difficult to interpret. To overcome this limitation, a new approach is proposed in this paper to directly estimate the self and mutual impedances of two coupled antennas from impedance correlations. The theoretical developments presented are validated experimentally in a reverberation chamber excited by a single antenna where mechanical and source stirring techniques are combined to generate a sufficiently diffuse field environment. It is shown, with antennas of different properties, that this approach allows to reconstruct with a good accuracy the complex impedance matrix between two receiving antennas as well as the transmission coefficient between them. The extracted gain pattern, in good agreement with that measured in an anechoic chamber, shows the good sensitivity of the proposed passive characterization technique.


Computing zerogroupvelocity points in anisotropic elastic waveguides: Globally and locally convergent methods Kiefer, D. A., B. Plestenjak, H. Gravenkamp, and C. Prada The Journal of the Acoustical Society of America 153, no. 2, 13861398 (2023)
Résumé: Dispersion curves of elastic waveguides exhibit points where the group velocity vanishes while the wavenumber remains finite. These are the socalled zerogroupvelocity (ZGV) points. As the elastodynamic energy at these points remains confined close to the source, they are of practical interest for nondestructive testing and quantitative characterization of structures. These applications rely on the correct prediction of the ZGV points. In this contribution, we first model the ZGV resonances in anisotropic plates based on the appearance of an additional modal solution. The resulting governing equation is interpreted as a twoparameter eigenvalue problem. Subsequently, we present three complementary numerical procedures capable of computing ZGV points in arbitrary nondissipative elastic waveguides in the conventional sense that their axial power flux vanishes. The first method is globally convergent and guarantees to find all ZGV points but can only be used for small problems. The second procedure is a very fast, generallyapplicable, Newtontype iteration that is locally convergent and requires initial guesses. The third method combines both kinds of approaches and yields a procedure that is applicable to large problems, does not require initial guesses and is likely to find all ZGV points. The algorithms are implemented in GEW ZGV computation (doi: 10.5281/zenodo.7537442).


Superresolved Imaging Based on Spatiotemporal WaveFront Shaping Noetinger, G., S. Métais, G. Lerosey, M. Fink, S. M. Popoff, and F. Lemoult Physical Review Applied 19, no. 2 (2023)
Résumé: A labelfree approach to improving the performances of confocal scanning imaging is proposed. We experimentally demonstrate its feasibility using acoustic waves. It relies on a way to encode spatial information using the temporal dimension. By moving an emitter, used to insonify an object, along a circular path, we create a temporally modulated wavefield. Because of the symmetries of the problem, the spatiotemporal input field can be decomposed into harmonics corresponding to different spatial vortices. Acquiring the backreflected waves with receivers that are also rotating, multiple images of the same object with different point spread functions are obtained. Not only is the resolution improved compared to a standard confocal configuration, but the accumulation of information also allows the building of images that beat the diffraction limit.


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.


Fullfield single molecule localization microscopy with a monodetector Lengauer, M., E. Fort, and S. LévêqueFort Biophysical Journal 122, no. 3S1, 133a (2023)


Comprehensive refractive manipulation of water waves using electrostriction Mouet, V., B. Apffel, and E. Fort Proceedings of the National Academy of Sciences of the United States of America 120, no. 6 (2023)
Résumé: The control of wave propagation based on refraction principles offers unparalleled possibilities as shown by the striking example of optics. This approach is unfortunately limited for water waves as it relies mainly on variations of the liquid depth which, while controlling the wave velocity, also trigger nonlinearities and damping. In this article, we show experimentally that electrostriction allows to implement extensive refractionbased control of water waves in a precise and contactless manner. The setup consists of an electrode under high voltage placed above the grounded conductive water. The waves propagating under the electrode can be slowed down up to approximately half their speed compared to free propagation. We characterize the SnellDescartes laws of refraction and the total internal reflection for the water waves. We implement emblematic refractionbased devices such as electrically tunable focusing lenses, waveguides without obstacles, and beam splitters based on frustrated internal reflection to perform interference experiments.


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.


Seismic surface wave focal spot imaging: numerical resolution experiments Giammarinaro, B., C. Tsarsitalidou, G. Hillers, J. De Rosny, L. Seydoux, S. Catheline, M. Campillo, and P. Roux Geophysical Journal International 232, no. 1, 201222 (2023)
Résumé: Numerical experiments of seismic wave propagation in a laterally homogeneous layered medium explore subsurface imaging at subwavelength distances for dense seismic arrays. We choose a timereversal approach to simulate fundamental mode Rayleigh surface wavefields that are equivalent to the crosscorrelation results of threecomponent ambient seismic field records. We demonstrate that the synthesized 2D spatial autocorrelation fields in the time domain support local or socalled focal spot imaging. Systematic tests involving clean isotropic surface wavefields but also interfering body wave components and anisotropic incidence assess the accuracy of the phase velocity and dispersion estimates obtained from focal spot properties. The results suggest that data collected within half a wavelength around the origin is usually sufficient to constrain the used Bessel functions models. Generally, the cleaner the surface wavefield the smaller the fitting distances that can be used to accurately estimate the local Rayleigh wave speed. Using models based on isotropic surface wave propagation we find that phase velocity estimates from verticalradial component data are less biased by Pwave energy compared to estimates obtained from verticalvertical component data, that even strong anisotropic surface wave incidence yields phase velocity estimates with an accuracy of 1 per cent or better, and that dispersion can be studied in the presence of noise. Estimates using a model to resolve potential medium anisotropy are significantly biased by anisotropic surface wave incidence. The overall accurate results obtained from nearfield measurements using isotropic medium assumptions imply that dense array seismic Rayleigh wave focal spot imaging can increase the depth sensitivity compared to ambient noise surface wave tomography. The analogy to elastography focal spot medical imaging implies that a high station density and clean surface wavefields support subwavelength resolution of lateral medium variations.


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.

