Multimodal highresolution retinal imaging using a camerabased DMDintegrated adaptive optics floodillumination ophthalmoscope Krafft, L., P. Senée, E. Gofas, O. Thouvenin, M. Atlan, M. Paques, S. Meimon, and P. Mecê Optics Letters 48, no. 14, 3785 (2023)


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)


A nonlinear delayed resonator for mimicking the hearing haircells Reda, J., M. Fink, and F. Lemoult Europhysics Letters 144, no. 3, 37001 (2023)


High timeresolved studies of stick–slip show similar dilatancy to fast and slow earthquakes Hu, W., Y. Ge, Q. Xu, R. Huang, Q. Zhao, H. Gou, M. Mcsaveney, C. Chang, Y. Li, X. Jia, and Y. Wang Proceedings of the National Academy of Sciences 120, no. 47 (2023)


Beating resonance patterns and extreme power flux skewing in anisotropic elastic plates Kiefer, D. A., S. Mezil, and C. Prada Science advances 9, no. 51, eadk6846 (2023)
Résumé: Elastic waves in anisotropic media can exhibit a power flux that is not collinear with the wave vector. This has notable consequences for waves guided in a plate. Through laserultrasonic experiments, we evidence remarkable phenomena due to slow waves in a singlecrystal silicon wafer. Waves exhibiting power flux orthogonal to their wave vector are identified. A pulsed line source that excites these waves reveals a wave packet radiated parallel to the line. Furthermore, there exist precisely eight plane waves with zero power flux. These socalled zerogroupvelocity modes are oriented along the crystal's principal axes. Time acts as a filter in the wavevector domain that selects these modes. Thus, a point source leads to beating resonance patterns with moving nodal curves on the surface of the infinite plate. We observe this pattern as it emerges naturally after a pulsed excitation.


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


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


Achiral Magnetic Photonic Antenna as a Tunable Nanosource of Chiral Light Cui, L., X. Yang, B. Reynier, C. Schwob, S. Bidault, B. Gallas, and M. Mivelle ACS Photonics 10, no. 11, 38503857 (2023)
Résumé: Sensitivity to molecular chirality is crucial for many fields, from biology and chemistry to the pharmaceutical industry. By generating superchiral light, nanophotonics has brought innovative solutions to reduce the detection volume and increase sensitivity at the cost of a nonselectivity of light chirality or a strong contribution to the background. Here, we theoretically propose a simple achiral plasmonic resonator based on a rectangular nanoslit in a thin metallic layer behaving as a magnetic dipole to generate a tunable nanosource of purely chiral light working from the UV to the infrared. This nanosource is free of any background, and the sign of its chirality is externally tunable in wavelength and polarization. These unique properties, resulting from the coupling between the incident wave and the magnetic dipolar character of our nanoantenna, coupled with a method of Fluorescent Detected Circular Dichroism (FDCD), shown to be 2 orders of magnitude more sensitive than classical circular dichroism measurements, thus provide a platform with deep subwavelength detection volumes for chiral molecules and a roadmap for optimizing the signaltonoise ratios in circular dichroism measurements to reach singlemolecule sensitivity.


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


Eventbased vision sensor for fast and dense singlemolecule localization microscopy Cabriel, C., T. Monfort, C. G. Specht, and I. Izeddin Nature Photonics 17, no. 12, 11051113 (2023)
Résumé: Singlemolecule localization microscopy (SMLM) enables crucial insights into cellular structures and processes to be revealed at the singlemolecule level. However, SMLM is often hampered by limited temporal resolution and the fixed frame rate of the acquisition. Here we present a new approach to SMLM data acquisition and processing based on an affordable eventbased sensor. This type of sensor reacts to changes in light intensity, rather than integrating photons during the exposure time of each frame. Each pixel works independently and returns a signal only when an intensity change is detected. Compared with video acquisition using traditional electronmultiplying chargecoupled device or scientific complementary metal–oxide–semiconductor cameras, the eventbased sensor provides higher temporal resolution and throughput on the positions of blinking molecules. We demonstrate eventbased SMLM superresolution imaging on biological samples with spatial resolution on a par with the performance of electronmultiplying chargecoupled device or scientific complementary metal–oxide–semiconductor cameras, while registering only the on and off switching of blinking molecules. We use eventbased SMLM to perform very dense singlemolecule imaging, where framebased cameras experience major limitations.


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.


Piezoorbital backaction force in a rareearthdoped crystal LouchetChauvet, A., P. Verlot, J. P. Poizat, and T. Chanelière Physical Review Applied 20, no. 5 (2023)
Résumé: We investigate a system composed of an ensemble of roomtemperature rareearth ions embedded in a bulk crystal, intrinsically coupled to internal strain via their sensitivity to the surrounding crystal field. We evidence the generation of a mechanical response under resonant atomic excitation. We find this motion to be the sum of two fundamental, resonant optomechanical backaction processes: a conservative, piezoorbital mechanism, resulting from the modification of the crystal field associated with the promotion of the ions to their excited state, and a dissipative, nonradiative photothermal process related to the phonons generated throughout the atomic population relaxation. Our work expands the horizons of research in hybrid optomechanics, and unveils unexplored interactions that may be key for understanding the dephasing dynamics of ultracoherent rareearth ions.


Imaging the Crustal and Upper Mantle Structure of the North Anatolian Fault: A Transmission Matrix Framework for Local Adaptive Focusing Touma, R., A. Le Ber, M. Campillo, and A. Aubry Journal of Geophysical Research: Solid Earth 128, no. 11 (2023)
Résumé: Imaging the structure of major fault zones is essential for our understanding of crustal deformations and their implications on seismic hazards. Investigating such complex regions presents several issues, including the variation of seismic velocity due to the diversity of geological units and the cumulative damage caused by earthquakes. Conventional migration techniques are in general strongly sensitive to the available velocity model. Here we apply a passive matrix imaging approach which is robust to the mismatch between this model and the real seismic velocity distribution. This method relies on the crosscorrelation of ambient noise recorded by a geophone array. The resulting set of impulse responses form a reflection matrix that contains all the information about the subsurface. In particular, the reflected body waves can be leveraged to: (a) determine the transmission matrix between the Earth's surface and any point in the subsurface; (b) build a confocal image of the subsurface reflectivity with a transverse resolution only limited by diffraction. As a study case, we consider seismic noise (0.1–0.5 Hz) recorded by the Dense Array for Northern Anatolia that consists of 73 stations deployed for 18 months in the region of the 1999 Izmit earthquake. Passive matrix imaging reveals the scattering structure of the crust and upper mantle around the North Anatolian Fault zone over a depth range of 60 km. The results show that most of the scattering is associated with the Northern branch that passes throughout the crust and penetrates into the upper mantle.


Imaging through a square multimode fiber by scanning focused spots with the memory effect Mezil, S., I. Wang, and E. Bossy Optics Letters 48, no. 17, 47014704 (2023)
Résumé: The existence of a shift–shift memory effect in square waveguides, whereby any translation of the input field induces translations in the output field in four symmetrical directions, has been previously observed by correlation measurements. Here we demonstrate that this memory effect is also observed in real space and can be put to use for imaging purposes. First, a focus is created at the output of a squarecore multimode fiber, by wavefront shaping based on feedback from a guidestar. Then, because of the memory effect, four symmetrical spots can be scanned at the fiber output by shifting the wavefront at the fiber input. We demonstrate that this property can be exploited to perform fluorescence imaging through the multimode fiber, without requiring the measurement of a transmission matrix.


Threedimensional ultrasound matrix imaging Bureau, F., J. Robin, A. Le Ber, W. Lambert, M. Fink, and A. Aubry Nature Communications 14, no. 1 (2023)
Résumé: Matrix imaging paves the way towards a next revolution in wave physics. Based on the response matrix recorded between a set of sensors, it enables an optimized compensation of aberration phenomena and multiple scattering events that usually drastically hinder the focusing process in heterogeneous media. Although it gave rise to spectacular results in optical microscopy or seismic imaging, the success of matrix imaging has been so far relatively limited with ultrasonic waves because wave control is generally only performed with a linear array of transducers. In this paper, we extend ultrasound matrix imaging to a 3D geometry. Switching from a 1D to a 2D probe enables a much sharper estimation of the transmission matrix that links each transducer and each medium voxel. Here, we first present an experimental proof of concept on a tissuemimicking phantom through exvivo tissues and then, show the potential of 3D matrix imaging for transcranial applications.


A Magnetic Monopole Antenna Reynier, B., X. Yang, B. Gallas, S. Bidault, and M. Mivelle ACS Photonics 10, no. 9, 30703076 (2023)
Résumé: Magnetic monopoles are hypothetical particles which, similar to the electric monopoles that generate electric fields, are at the origin of magnetic fields. Despite many efforts, to date, these theoretical particles have yet to be observed. Nevertheless, many systems or physical phenomena mimic the behavior of magnetic monopoles. Here, we propose a new type of photonic nanoantenna behaving as a radiating magnetic monopole. We demonstrate that a halfnanoslit in a semiinfinite gold layer generates a single pole of enhanced magnetic field at the nanoscale and that this single pole radiates efficiently in the far field. We also introduce an effective magnetic charge using Gauss’s law of magnetism, in analogy to the electric charge, which further highlights the monopolar behavior of this new antenna. Finally, we show that different plasmonic and metallic materials can provide magnetic monopole antennas covering the visibletonear infrared range, even down to GHz frequencies. This original antenna concept opens the way to a new model system to study magnetic monopoles and a new optical magnetic field source to study “magnetic lightmatter coupling.” Furthermore, it shows potential applications at lower frequencies, such as in magnetic resonance imaging.


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


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


Repetitive small seismicity coupled with rainfall can trigger large slope instabilities on metastable volcanic edifices Durand, V., A. Mangeney, P. Bernard, X. Jia, F. Bonilla, C. Satriano, J. M. Saurel, E. M. Aissaoui, A. Peltier, V. Ferrazzini, P. Kowalski, F. Lauret, C. Brunet, and C. Hibert Communications Earth and Environment 4, no. 1 (2023)
Résumé: Quantifying the effect of external forcings like seismicity or rain on slope destabilization is a longstanding and challenging issue. To investigate the respective roles of these forcings, we analyze an unprecedented 10year long catalog of rockfalls occurring in the crater of the Piton de la Fournaise volcano (La Reunion Island), using statistical tools originally developed for earthquakes. Our analysis reveals the predominant effect of low amplitude repetitive seismicity in the triggering of rockfalls located at a few kilometers from the source, due to progressive damaging of the slope. Moreover, we show that the efficiency and timedelay of this dynamic triggering is controlled by the stability state of the slope, i.e. its closeness to the failure, as observed with labexperiments on metastable granular slopes. Our results show the need to account for longterm swarmtype seismic activity that can affect the stability of geological structures like slopes and faults, but also buildings.


Inverse design of alldielectric metasurfaces with accidental bound states in the continuum Gladyshev, S., T. D. Karamanos, L. Kuhn, D. Beutel, T. Weiss, C. Rockstuhl, and A. Bogdanov Nanophotonics 12, no. 19, 37673779 (2023)
Résumé: Metasurfaces with bound states in the continuum (BICs) have proven to be a powerful platform for drastically enhancing lightmatter interactions, improving biosensing, and precisely manipulating near and farfields. However, engineering metasurfaces to provide an ondemand spectral and angular position for a BIC remains a prime challenge. A conventional solution involves a fine adjustment of geometrical parameters, requiring multiple timeconsuming calculations. In this work, to circumvent such tedious processes, we develop a physicsinspired, inverse design method on alldielectric metasurfaces for an ondemand spectral and angular position of a BIC. Our suggested method predicts the coreshell particles that constitute the unit cell of the metasurface, while considering practical limitations on geometry and available materials. Our method is based on a smart combination of a semianalytical solution, for predicting the required dipolar Mie coefficients of the metaatom, and a machine learning algorithm, for finding a practical design of the metaatom that provides these Mie coefficients. Although our approach is exemplified in designing a metasurface sustaining a BIC, it can, also, be applied to many more objective functions. With that, we pave the way toward a general framework for the inverse design of metasurfaces in specific and nanophotonic structures in general.


The mesencephalic locomotor region recruits V2a reticulospinal neurons to drive forward locomotion in larval zebrafish CarboTano, M., M. Lapoix, X. Jia, O. Thouvenin, M. Pascucci, F. Auclair, F. B. Quan, S. Albadri, V. Aguda, Y. Farouj, E. M. C. Hillman, R. Portugues, F. Del Bene, T. R. Thiele, R. Dubuc, and C. Wyart Nature Neuroscience 26, no. 10, 17751790 (2023)
Résumé: The mesencephalic locomotor region (MLR) is a brain stem area whose stimulation triggers graded forward locomotion. How MLR neurons recruit downstream vsx2 + (V2a) reticulospinal neurons (RSNs) is poorly understood. Here, to overcome this challenge, we uncovered the locus of MLR in transparent larval zebrafish and show that the MLR locus is distinct from the nucleus of the medial longitudinal fasciculus. MLR stimulations reliably elicit forward locomotion of controlled duration and frequency. MLR neurons recruit V2a RSNs via projections onto somata in pontine and retropontine areas, and onto dendrites in the medulla. Highspeed volumetric imaging of neuronal activity reveals that strongly MLRcoupled RSNs are active for steering or forward swimming, whereas weakly MLRcoupled medullary RSNs encode the duration and frequency of the forward component. Our study demonstrates how MLR neurons recruit specific V2a RSNs to control the kinematics of forward locomotion and suggests conservation of the motor functions of V2a RSNs across vertebrates.


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


Dynamic fullfield optical coherence tomography module adapted to commercial microscopes allows longitudinal in vitro cell culture study Monfort, T., S. Azzollini, J. Brogard, M. Clémençon, A. SlembrouckBrec, V. Forster, S. Picaud, O. Goureau, S. Reichman, O. Thouvenin, and K. Grieve Communications Biology 6, no. 1, 992 (2023)
Résumé: Dynamic fullfield optical coherence tomography (DFFOCT) has recently emerged as a labelfree imaging tool, capable of resolving cell types and organelles within 3D live samples, whilst monitoring their activity at tens of milliseconds resolution. Here, a DFFOCT module design is presented which can be coupled to a commercial microscope with a stage top incubator, allowing noninvasive labelfree longitudinal imaging over periods of minutes to weeks on the same sample. Long term volumetric imaging on human induced pluripotent stem cellderived retinal organoids is demonstrated, highlighting tissue and cell organization processes such as rosette formation and mitosis as well as cell shape and motility. Imaging on retinal explants highlights single 3D cone and rod structures. An optimal workflow for data acquisition, postprocessing and saving is demonstrated, resulting in a time gain factor of 10 compared to prior state of the art. Finally, a method to increase DFFOCT signaltonoise ratio is demonstrated, allowing rapid organoid screening.


Measuring Dirac cones in a brickwall lattice microwave metamaterial Li, B., S. Yves, A. Delory, S. Liu, M. Fink, and F. Lemoult Physical Review B 108, no. 9 (2023)
Résumé: The intriguing discovery of bidimensional structures in solidstate physics has motivated the seeking of their analogs in many fields. In this paper, we propose a general scheme to achieve Dirac cones in the microwave domain. It is based on a bidimensional locally resonant metamaterial ruled by a tightbinding Hamiltonian with asymmetric coupling. By specifically controlling the hopping links between metaatoms, the Dirac cones can be moved in the first Brillouin zone. A proof of this assertion is performed theoretically, numerically, and experimentally using a brickwall lattice of resonant metallic wires. The results directly evidence that the crystalline description of a subwavelengthscaled microwave system provides a really convenient tabletop platform for investigating the tempting challenges offered in solidstate physics.


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


Shaping single photons through multimode optical fibers using mechanical perturbations Shekel, R., O. Lib, R. GutierrezCuevas, S. M. Popoff, A. Ling, and Y. Bromberg APL Photonics 8, no. 9, 096109 (2023)
Résumé: Multimode optical fibers support lowloss transmission of multiple spatial modes, allowing for the transport of highdimensional, spatially encoded information. In particular, encoding quantum information in the transverse shape of photons may boost the capacity of quantum channels while using existing infrastructure. However, when photons propagate through a multimode fiber, their transverse shape gets scrambled because of mode mixing and modal interference. This is usually corrected using freespace spatial light modulators, inhibiting a robust allfiber operation. In this work, we demonstrate an allfiber approach for controlling the shape of single photons and the spatial correlations between entangled photon pairs, using carefully controlled mechanical perturbations of the fiber. We optimize these perturbations to localize the spatial distribution of a single photon or the spatial correlations of photon pairs in a single spot, enhancing the signal in the optimized spot by over an order of magnitude. Using the same approach, we show a similar enhancement for coupling light from a multimode fiber into a singlemode fiber.
Motsclés: wavefront shaping; entenglement; quantum optics; multimode fibers


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.

