Matrix imaging as a tool for high-resolution monitoring of deep volcanic plumbing systems with seismic noise Giraudat, E., A. Burtin, A. Le Ber, M. Fink, J. C. Komorowski, and A. Aubry Communications Earth and Environment 5, no. 1 (2024)
Résumé: Volcanic eruptions necessitate precise monitoring of magma pressure and inflation for improved forecasting. Understanding deep magma storage is crucial for hazard assessment, yet imaging these systems is challenging due to complex heterogeneities that disrupt standard seismic migration techniques. Here we map the magmatic and hydrothermal system of the La Soufrière volcano in Guadeloupe by analyzing seismic noise data from a sparse geophone array under a matrix formalism. Seismic noise interferometry provides a reflection matrix containing the signature of echoes from deep heterogeneities. Using wave correlations resistant to disorder, matrix imaging successfully unscrambles wave distortions, revealing La Soufrière’s internal structure down to 10 km with 100 m resolution. This method surpasses the diffraction limit imposed by geophone array aperture, providing crucial data for modeling and high-resolution monitoring. We see matrix imaging as a revolutionary tool for understanding volcanic systems and enhancing observatories’ abilities to monitor dynamics and forecast eruptions. (Figure presented.)
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Characterization and Exploitation of the Rotational Memory Effect in Multimode Fibers Gutiérrez-Cuevas R., , Goetschy A., Bromberg Y., Pelc G., Ravn Andresen E., Bigot L., Quiquempois Y, Bsaibes M, Sillard P., Bigot M., Katz O., De Rosny J., and Popoff S. M. Physical Review X 14, no. 3, 031046 (2024)
Résumé: In an ideal perfectly straight multimode fiber with a circular core, the symmetry ensures that rotating the input wave front leads to a corresponding rotation of the output wave front. This invariant property, known as the rotational memory effect (RME), remains independent of the typically unknown output profile. The RME thus offers significant potential for imaging and telecommunication applications. However, in real-life fibers, this effect is degraded by intrinsic imperfections and external perturbations, and is challenging to observe because of its acute sensitivity to misalignments and aberrations in the optical setup. Building on a previously established method for precisely estimating fiber transmission properties, we demonstrate an accurate extraction of RME properties. Additionally, we introduce a comprehensive theoretical framework for both qualitative and quantitative analysis, which specifically links the angular-dependent correlation of the RME to the core deformation’s geometrical properties and the fiber’s mode characteristics. Our theoretical predictions align well with experimental data and simulations for various amounts of fiber distorsion. Finally, we demonstrate the ability to engineer wave fronts with significantly enhanced correlation across all rotation angles. This work enables accurate characterization of distributed disorder from the fabrication process and facilitates calibration-free imaging in multimode fibers.
Mots-clés: multimode fiber; wavefront shaping; correlation; memory effect; imaging; telecommunications
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Recovering particle velocity and size distributions in ejecta with photon Doppler velocimetry Don Jayamanne, J. A., R. Outerovitch, F. Ballanger, J. Bénier, E. Blanco, C. Chauvin, P. Hereil, J. Tailleur, O. Durand, R. Pierrat, R. Carminati, A. Hervouët, P. Gandeboeuf, and J. R. Burie Journal of Applied Physics 136, no. 8 (2024)
Résumé: When a solid metal is struck, its free surface can eject fast and fine particles. Despite the many diagnostics that have been implemented to measure the mass, size, velocity, or temperature of ejecta, these efforts provide only a partial picture of this phenomenon. Ejecta characterization, especially in constrained geometries, is an inherently ill-posed problem. In this context, Photon Doppler Velocimetry (PDV) has been a valuable diagnostic, measuring reliably particles and free surface velocities in the single scattering regime. Here, we present ejecta experiments in gas and how, in this context, PDV allows one to retrieve additional information on the ejecta, i.e., information on the particles’ size. We explain what governs ejecta transport in gas and how it can be simulated. To account for the multiple scattering of light in these ejecta, we use the Radiative Transfer Equation (RTE) that quantitatively describes PDV spectrograms, and their dependence not only on the velocity but also on the size distribution of the ejecta. We remind how spectrograms can be simulated by solving numerically this RTE and we show how to do so on hydrodynamic ejecta simulation results. Finally, we use this complex machinery in different ejecta transport scenarios to simulate the corresponding spectrograms. Comparing these to experimental results, we iteratively constrain the ejecta description at an unprecedented level. This work demonstrates our ability to recover particle size information from what is initially a velocity diagnostic, but more importantly it shows how, using existing simulation of ejecta, we capture through simulation the complexity of experimental spectrograms.
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Harnessing forward multiple scattering for optical imaging deep inside an opaque medium Najar, U., V. Barolle, P. Balondrade, M. Fink, C. Boccara, and A. Aubry Nature Communications 15, no. 1 (2024)
Résumé: As light travels through a disordered medium such as biological tissues, it undergoes multiple scattering events. This phenomenon is detrimental to in-depth optical microscopy, as it causes a drastic degradation of contrast, resolution and brightness of the resulting image beyond a few scattering mean free paths. However, the information about the inner reflectivity of the sample is not lost; only scrambled. To recover this information, a matrix approach of optical imaging can be fruitful. Here, we report on a de-scanned measurement of a high-dimension reflection matrix R via low coherence interferometry. Then, we show how a set of independent focusing laws can be extracted for each medium voxel through an iterative multi-scale analysis of wave distortions contained in R. It enables an optimal and local compensation of forward multiple scattering paths and provides a three-dimensional confocal image of the sample as the latter one had become digitally transparent. The proof-of-concept experiment is performed on a human opaque cornea and an extension of the penetration depth by a factor five is demonstrated compared to the state-of-the-art.
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A practical guide to digital micro-mirror devices (DMDs) for wavefront shaping Popoff, S. M., R. Gutiérrez-Cuevas, Y. Bromberg, and M. W. Matthés Journal of Physics: Photonics 6, no. 4, 043001 (2024)
Résumé: Digital micromirror devices have gained popularity in wavefront shaping, offering a high frame rate alternative to liquid crystal spatial light modulators. They are relatively inexpensive, offer high resolution, are easy to operate, and a single device can be used in a broad optical bandwidth. However, some technical drawbacks must be considered to achieve optimal performance. These issues, often undocumented by manufacturers, mostly stem from the device's original design for video projection applications. Herein, we present a guide to characterize and mitigate these effects. Our focus is on providing simple and practical solutions that can be easily incorporated into a typical wavefront shaping setup.
Mots-clés: wavefront shaping; modulation; optics; DMD; modulator; SLM
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Closed forms for spatiotemporal optical vortices and sagittal skyrmionic pulses Vo, S., R. Gutiérrez-Cuevas, and M. A. Alonso Journal of Optics (United Kingdom) 26, no. 9 (2024)
Résumé: Spatiotemporal optical vortices (STOVs) are short pulses that present a vortex whose axis is perpendicular to the main propagation direction. We present analytic expressions for these pulses that satisfy exactly Maxwell’s equation, by applying appropriate differential operators to complex focus pulses with Poisson-like frequency spectrum. We also provide a simple ray picture for understanding the deformation of these pulses under propagation. Finally, we use these solutions to propose a type of pulse with sagittal skyrmionic polarization distribution covering all states of transverse polarization.
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Perfect active absorption of water waves in a channel by a dipole source Euvé, L. P., K. Pham, P. Petitjeans, V. Pagneux, and A. Maurel Journal of Fluid Mechanics 990 (2024)
Résumé: This study investigates the potential use of an active device to efficiently absorb water waves propagating in a channel. The active device comprises a dipole source consisting of two sources in quasi-opposition of phase. We explore the feasibility of this approach to achieve perfect absorption of guided waves through interference phenomena. To accomplish this, we establish the law governing the waves emitted by the dipole source to optimize the absorption of specific incident waves. The validity of this law is demonstrated through numerical simulations and laboratory experiments, encompassing both the harmonic and transient regimes of the experimental set-up.
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Simulated Slidequakes: Insights From DEM Simulations Into the High-Frequency Seismic Signal Generated by Geophysical Granular Flows Arran, M. I., A. Mangeney, J. De Rosny, and R. Toussaint Journal of Geophysical Research: Earth Surface 129, no. 8 (2024)
Résumé: Geophysical granular flows generate seismic signals known as “slidequakes” or “landquakes”, with low-frequency components whose generation by mean forces is widely used to infer hazard-relevant flow properties. Many more such properties could be inferred by understanding the fluctuating forces that generate slidequakes' higher frequency components and, to do so, we conducted discrete-element simulations that examined the fluctuating forces exerted by steady, downslope-periodic granular flows on fixed, rough bases. Unlike our previous laboratory experiments, our simulations precluded basal slip. We show that, in its absence, simulated basal forces' power spectra have high-frequency components more accurately predicted using mean shear rates than using depth-averaged flow velocities, and can have intermediate-frequency components which we relate to chains of prolonged interparticle contacts. We develop a “minimal model”, which uses a flow's collisional properties to even more accurately predict the high-frequency components, and empirically parametrize this model in terms of mean flow properties, for practical application. Finally, we demonstrate that the bulk inertial number determines not only the magnitude ratio of rapidly fluctuating and mean forces on a unit basal area, consistent with previous experimental results, but also the relative magnitudes of the high and intermediate-frequency force components.
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Automated Detection of Mental Stress Using Multimodal Characterization of PPG Signal for AI Based Healthcare Applications Paul, A., A. Chakraborty, D. Sadhukhan, S. Pal, and M. Mitra SN Computer Science 5, no. 6 (2024)
Résumé: Purpose-The increasing complexity of our society has made mental stress a part of every human life. The early evaluation of long-term mental stress conditions is necessary since they may trigger a number of chronic disorders. Existing electroencephalogram (EEG) based methods for estimating mental stress are often complex, multi-channel, and expert-dependent. On the other hand, the respiratory signal offers intriguing information about stress, but its capture is challenging and requires multimodal support. Method-To overcome this challenge, the respiratory signal can be extracted from the Photoplethysmogram (PPG) signal. The easy-to-acquire PPG signal is multimodally characterised in this proposed approach to determine the stressed status. Exclusively, the created algorithm leverages a major PPG characteristic and, using streamlined approaches, additionally extracts the respiratory rate from the same PPG signal. The method is assessed using PPG records gathered from the publicly available DEAP dataset. Result-A simple threshold-based along with standard classification techniques are used to assess the effectiveness of the proposed algorithm, which classify the stressed and relaxed states with an average accuracy of 98.43%. The suggested approach outperforms the existing methods in terms of performance, and its simple methodology and low acquisition load support its use in real-time standalone, personal healthcare applications. Conclusion-The use of simple features and classification strategy ensures the applicability of the proposed method in artificial intelligence (AI) based healthcare applications. This will upgrade the existing system for monitoring and proper diagnosis of patients suffering from mental stress conditions.
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Reaching the precision limit with tensor-based wavefront shaping Gutiérrez-Cuevas, R., D. Bouchet, J. De Rosny, and S. M. Popoff Nature Communications 15, no. 1 (2024)
Résumé: Perturbations in complex media, due to their own dynamical evolution or to external effects, are often seen as detrimental. Therefore, a common strategy, especially for telecommunication and imaging applications, is to limit the sensitivity to those perturbations in order to avoid them. Here, instead, we consider enhancing the interaction between light and perturbations to produce the largest change in the output intensity distribution. Our work hinges on the use of tensor-based techniques, presently at the forefront of machine learning explorations, to study intensity-based measurements where its quadratic relationship to the field prevents the use of standard matrix methods. With this tensor-based framework, we can identify the maximum-information intensity channel which maximizes the change in its output intensity distribution and the Fisher information encoded in it about a given perturbation. We further demonstrate experimentally its superiority for robust and precise sensing applications. Additionally, we derive the appropriate strategy to reach the precision limit for intensity-based measurements, leading to an increase in Fisher information by more than four orders of magnitude compared to the mean for random wavefronts when measured with the pixels of a camera.
Mots-clés: wavefront shaping, multimode fiber, sensing, information, transmission matrix, optical fibers
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Versatile, fast, and accurate frequency excursions with a semiconductor laser Llauze, T., F. Montjovet-Basset, and A. Louchet-Chauvet Applied Optics 63, no. 19, 5192-5202 (2024)
Résumé: Achieving accurate arbitrary frequency excursions with a laser can be quite a technical challenge, especially when steep slopes (GHz/μs) are required, due to both deterministic and stochastic frequency fluctuations. In this work we present a multistage correction combining four techniques: pre-distorsion of the laser modulation, iterative correction, opto-electronic feedback loop, and feed-forward correction. This combination allows us not only to compensate for the non-instantaneous response of the laser to an input modulation but also to correct in real time the stochastic frequency fluctuations.We implement this multistage architecture on a commercial DBR laser and verify its efficiency, first, with monochromatic operation, and second, with highly demanding frequency excursions. We demonstrate that our multistage correction not only enables a strong reduction of the laser linewidth but also allows steep frequency excursions with a relativeRMSfrequency errorwell below1%and a laser spectral purity consistently better than 100 kHz, even in the midst of gigahertz-scale frequency excursions.
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Variation in Granular Frictional Resistance Across Nine Orders of Magnitude in Shear Velocity Gou, H. X., W. Hu, Q. Xu, J. Chen, M. J. Mcsaveney, E. C. P. Breard, R. Q. Huang, Y. J. Wang, X. P. Jia, and L. Zhou Journal of Geophysical Research: Solid Earth 129, e2023JB028241 (2024)
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Foveolar Drusen Decrease Fixation Stability in Pre-Symptomatic AMD Murari, J., J. Gautier, J. Daout, L. Krafft, P. Senée, P. Mecê, K. Grieve, W. Seiple, D. Sheynikhovich, S. Meimon, M. Paques, and A. Arleo Investigative Ophthalmology & Visual Science 65, no. 8, 13 (2024)
Résumé: Purpose: This study aims at linking subtle changes of fixational eye movements (FEM) in controls and in patients with foveal drusen using adaptive optics retinal imaging in order to find anatomo-functional markers for pre-symptomatic age-related macular degeneration (AMD). Methods: We recruited 7 young controls, 4 older controls, and 16 patients with presymptomatic AMD with foveal drusen from the Silversight Cohort. A high-speed research-grade adaptive optics flood illumination ophthalmoscope (AO-FIO) was used for monocular retinal tracking of fixational eye movements. The system allows for sub-arcminute resolution, and high-speed and distortion-free imaging of the foveal area. Foveal drusen position and size were documented using gaze-dependent imaging on a clinical-grade AO-FIO. Results: FEM were measured with high precision (RMS-S2S = 0.0015 degrees on human eyes) and small foveal drusen (median diameter = 60 µm) were detected with high contrast imaging. Microsaccade amplitude, drift diffusion coefficient, and ISOline area (ISOA) were significantly larger for patients with foveal drusen compared with controls. Among the drusen participants, microsaccade amplitude was correlated to drusen eccentricity from the center of the fovea. Conclusions: A novel high-speed high-precision retinal tracking technique allowed for the characterization of FEM at the microscopic level. Foveal drusen altered fixation stability, resulting in compensatory FEM changes. Particularly, drusen at the foveolar level seemed to have a stronger impact on microsaccade amplitudes and ISOA. The unexpected anatomo-functional link between small foveal drusen and fixation stability opens up a new perspective of detecting oculomotor signatures of eye diseases at the presymptomatic stage.
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Variation in Granular Frictional Resistance Across Nine Orders of Magnitude in Shear Velocity Gou, H. X., W. Hu, Q. Xu, J. Chen, M. J. Mcsaveney, E. C. P. Breard, R. Q. Huang, Y. J. Wang, X. P. Jia, and L. Zhou Journal of Geophysical Research: Solid Earth 129, no. 7 (2024)
Résumé: Determining the shear-velocity dependence of dry granular friction can provide insight into the controlling variables in a dry granular friction law. Some laboratories believe that the quality of this study is at the forefront of the discipline for the following reasons. Results suggest that granular friction is greatly affected by shear-velocity (v), but shear experiments over the large range of naturally occurring shear-velocities are lacking. Herein we examined the shear velocity dependence of dry friction for three granular materials, quartz sand, glass beads and fluorspar, across nine orders of magnitude of shear velocity (10−8–2 m/s). Within this range, granular friction exhibited four regimes, following a broad approximate “m” shape including two velocity-strengthening and two velocity-weakening regimes. We discuss the possible physical mechanisms of each regime. This shear velocity dependence appeared to be universal for all particle types, shapes, sizes, and for all normal stresses over the tested range. We also found that ultra-high frequency vibration as grain surfaces were scoured by micro-chips were formed by spalling at high shear velocities, creating ∼20 μm diameter impact pits on particle surfaces. This study provides laboratory laws of a friction-velocity (μ-v) model for granular materials.
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Anderson mobility edge as a percolation transition Filoche, M., P. Pelletier, D. Delande, and S. Mayboroda Physical Review B 109, no. 22 (2024)
Résumé: The location of the mobility edge is a long-standing problem in Anderson localization. In this Letter, we show that the effective confining potential introduced in the localization landscape (LL) theory predicts the onset of delocalization in 3D tight-binding models in a large part of the energy-disorder diagram. Near the edge of the spectrum, the eigenstates are confined inside the basins of the LL-based potential. The delocalization transition corresponds to the progressive merging of these basins, resulting in the percolation of this classically allowed region throughout the system. This approach, shown to be valid both in the cases of uniform and binary disorders despite their very different phase diagrams, allows us to reinterpret the Anderson transition in the tight-binding model: the mobility edge appears to be composed of two parts, one being understood as a percolation transition.
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Tutorial: How to build and control an all-fiber wavefront modulator using mechanical perturbations Shekel, R., K. Sulimany, S. Resisi, Z. Finkelstein, O. Lib, S. M. Popoff, and Y. Bromberg Journal of Physics: Photonics 6, no. 3, 033002 (2024)
Résumé: Multimode optical fibers support the dense, low-loss transmission of many spatial modes, making them attractive for technologies such as communications and imaging. However, information propagating through multimode fibers is scrambled, due to modal dispersion and mode mixing. This is usually rectified using wavefront shaping techniques with devices such as spatial light modulators. Recently, we demonstrated an all-fiber system for controlling light propagation inside multimode fibers using mechanical perturbations, called the fiber piano. In this tutorial we explain the design considerations and experimental methods needed to build a fiber piano, and review applications where fiber pianos have been used.
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Effective-medium approach to the resonance distribution of wave scattering in a random point field Gaspard, D., and J. M. Sparenberg Physical Review A 109, no. 6 (2024)
Résumé: In a previous paper [Phys. Rev. A 105, 042205 (2022)10.1103/PhysRevA.105.042205], the distribution of resonance poles in the complex plane of the wave number k associated to the multiple scattering of a quantum particle in a random point field was numerically discovered. This distribution presented two distinctive structures: a set of peaks at small k when the wavelength is larger than the interscatterer distance and a band almost parallel to the real axis at larger k. In this paper, a theoretical study based on wave transport theory is proposed to explain the origin of these structures and to predict their distribution in the complex k plane. First, it is shown that the peaks at small k can be understood using the effective wave equation for the average wave function over the disorder. Then, that the band at large k can be described by the Bethe-Salpeter equation for the square modulus of the wave function. This study is supported by careful comparisons with numerical simulations.
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Wideband and low-spurious optical waveform generator for optically addressable quantum systems manipulation and control Welinski, S., E. Beattie, L. Ulrich, S. Wengerowsky, H. De Riedmatten, L. Morvan, and P. Berger Optics Express 32, no. 12, 20992-21006 (2024)
Résumé: Optical manipulation of quantum systems requires stable laser sources able to produce complex waveforms over a large frequency range. In the visible region, such waveforms can be generated using an acousto-optic modulator driven by an arbitrary waveform generator, but these suffer from a limited tuning range typically of a few tens of MHz. Visible-range electro-optic modulators are an alternative option offering a larger modulation bandwidth, however they have limited output power which drastically restricts the scalability of quantum applications. There is currently no architecture able to perform phase-stabilized waveforms over several GHz in the visible or near infrared region while providing sufficient optical power for quantum applications. Here we propose and develop a modulation and frequency conversion set-up able to deliver optical waveforms over a large frequency range, with a high spurious extinction ratio, scalable to the entire visible/near infrared region with high optical power. The optical waveforms are first generated at telecom wavelength and then converted to the emitter wavelength through a sum frequency generation process. By adapting the pump laser frequency, the optical waveforms can be tuned to interact with a broad range of optical quantum emitters or qubits such as alkali atoms, trapped ions, rare earth ions, or fluorescent defects in solid-state matrices. Using this architecture, we were able to detect and study a single erbium ion in a nanoparticle. We also generated high bandwidth signals at 606 nm, which would enable frequency multiplexing of on-demand read-out Pr3+:Y2SiO5 quantum memories.
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Symmetry-breaking-induced off-resonance second-harmonic generation enhancement in asymmetric plasmonic nanoparticle dimers Wang, Y., Z. Peng, Y. De Wilde, and D. Lei Nanophotonics (2024)
Résumé: The linear and nonlinear optical properties of metallic nanoparticles have attracted considerable experimental and theoretical research interest. To date, most researchers have focused primarily on exploiting their plasmon excitation enhanced near-field and far-field responses and related applications in sensing, imaging, energy harvesting, conversion, and storage. Among numerous plasmonic structures, nanoparticle dimers, being a structurally simple and easy-to-prepare system, hold significant importance in the field of nanoplasmonics. In highly symmetric plasmonic nanostructures, although the odd-order optical nonlinearity of the near-surface region will be improved because of the enhanced near-fields, even-order nonlinear processes such as second-harmonic generation (SHG) will still be quenched and thus optically forbidden. Under this premise, it is imperative to introduce structural symmetry breaking to realize plasmon-enhanced even-order optical nonlinearity. Here, we fabricate a series of nanoparticle dimers each composed of two gold nanospheres with different diameters and subsequently investigate their structural asymmetry dependent linear and nonlinear optical properties. We find that the SHG intensities of gold nanosphere dimers are significantly enhanced by structural asymmetry under off-resonance excitation while the plasmonic near-field enhancement mainly affects SHG under on-resonance excitation. Our results reveal that symmetry breaking will play an indispensable role when designing novel coupled plasmonic nanostructures with enhanced nonlinear optical properties.
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Cellular structural and functional imaging of donor and pathological corneas with label-free dual-mode full-field optical coherence tomography Fei, K., Z. Luo, Y. Chen, Y. Huang, S. Li, V. Mazlin, A. C. Boccara, J. Yuan, and P. Xiao Biomedical Optics Express 15, no. 6, 3869-3888 (2024)
Résumé: In this study, a dual-mode full-field optical coherence tomography (FFOCT) was customized for label-free static and dynamic imaging of corneal tissues, including donor grafts and pathological specimens. Static images effectively depict relatively stable structures such as stroma, scar, and nerve fibers, while dynamic images highlight cells with active intracellular metabolism, specifically for corneal epithelial cells. The dual-mode images complementarily demonstrate the 3D microstructural features of the cornea and limbus. Dual-modal imaging reveals morphological and functional changes in corneal epithelial cells without labeling, indicating cellular apoptosis, swelling, deformation, dynamic signal alterations, and distinctive features of inflammatory cells in keratoconus and corneal leukoplakia. These findings propose dual-mode FFOCT as a promising technique for cellular-level cornea and limbus imaging.
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Label-Free Imaging of Inflammation at the Level of Single Cells in the Living Human Eye Rui, Y., M. Zhang, D. M. W. Lee, V. C. Snyder, R. Raghuraman, E. Gofas-Salas, P. Mecê, S. Yadav, P. Tiruveedhula, K. Grieve, J. A. Sahel, M. H. Errera, and E. A. Rossi Ophthalmology Science 4, no. 5, 100475 (2024)
Résumé: Purpose: Putative microglia were recently detected using adaptive optics ophthalmoscopy in healthy eyes. Here we evaluate the use of nonconfocal adaptive optics scanning light ophthalmoscopy (AOSLO) for quantifying the morphology and motility of presumed microglia and other immune cells in eyes with retinal inflammation from uveitis and healthy eyes. Design: Observational exploratory study. Participants: Twelve participants were imaged, including 8 healthy participants and 4 posterior uveitis patients recruited from the clinic of 1 of the authors (M.H.E.). Methods: The Pittsburgh AOSLO imaging system was used with a custom-designed 7-fiber optical fiber bundle for simultaneous confocal and nonconfocal multioffset detection. The inner retina was imaged at several locations at multiple timepoints in healthy participants and uveitis patients to generate time-lapse images. Main Outcome Measures: Microglia and macrophages were manually segmented from nonconfocal AOSLO images, and their morphological characteristics quantified (including soma size, diameter, and circularity). Cell soma motion was quantified across time for periods of up to 30 minutes and their speeds were calculated by measuring their displacement over time. Results: A spectrum of cell morphologies was detected in healthy eyes from circular amoeboid cells to elongated cells with visible processes, resembling activated and ramified microglia, respectively. Average soma diameter was 16.1 ± 0.9 μm. Cell movement was slow in healthy eyes (0.02 μm/sec on average), but macrophage-like cells moved rapidly in some uveitis patients (up to 3 μm/sec). In an eye with infectious uveitis, many macrophage-like cells were detected; during treatment their quantity and motility decreased as vision improved. Conclusions: In vivo adaptive optics ophthalmoscopy offers promise as a potentially powerful tool for detecting and monitoring inflammation and response to treatment at a cellular level in the living eye. Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.
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Delivering broadband light deep inside diffusive media Mcintosh, R., A. Goetschy, N. Bender, A. Yamilov, C. W. Hsu, H. Yılmaz, and H. Cao Nature Photonics (2024)
Résumé: Wavefront shaping enables the targeted delivery of coherent light into random-scattering media, such as biological tissue, by the constructive interference of scattered waves. However, broadband waves have short coherence times, weakening the interference effect. Here we introduce a broadband deposition matrix that identifies a single input wavefront that maximizes the broadband energy delivered to an extended target deep inside a diffusive system. We experimentally demonstrate that long-range spatial and spectral correlations result in sixfold energy enhancement for targets containing 1,700 speckle grains and located at a depth of up to ten transport mean free paths, even when the coherence time is an order of magnitude shorter than the diffusion dwell time of light in the scattering sample. In the broadband (fast decoherence) limit, enhancement of energy delivery to extended targets becomes nearly independent of the target depth and dissipation. Our experiments, numerical simulations and analytic theory establish the fundamental limit for broadband energy delivery deep into a diffusive system, which has important consequences for practical applications.
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Solution to the cocktail party problem: A time-reversal active metasurface for multipoint focusing Bourdeloux, C., M. Fink, and F. Lemoult Physical Review Applied 21, no. 5, 054039 (2024)
Résumé: The cocktail party effect is the capability to focus one's auditory attention on particular audio sources while ignoring other audio sources. We propose an experimental strategy to reproduce this ability by designing a time-dependent metasurface composed of independent active mirrors. Each active mirror is a programmable acoustic unit cell capable of hearing, computing, and re-emitting acoustic signals: each of them acts as a convolution filter. The proper configuration of the metasurface temporal filters allows one to establish an acoustic communication link between groups of individuals immersed in the noisy environment: a multiple-user multiple-input, multiple-output acoustic system is built.
Mots-clés: metasurface;cocktail party;time reversal
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Influence of static and dynamic ocular aberrations on full-field optical coherence tomography for in vivo high-resolution retinal imaging Cai, Y., O. Thouvenin, K. Grieve, and P. Mecê Optics Letters 49, no. 9, 2209-2212 (2024)
Résumé: Under spatially incoherent illumination, time-domain full-field optical coherence tomography (FFOCT) offers the possibility to achieve in vivo retinal imaging at cellular resolution over a wide field of view. Such performance is possible, albeit there is the presence of ocular aberrations even without the use of classical adaptive optics. While the effect of aberrations in FFOCT has been debated these past years, mostly on low-order and static aberrations, we present, for the first time to our knowledge, a method enabling a quantitative study of the effect of statistically representative static and dynamic ocular aberrations on FFOCT image metrics, such as SNR, resolution, and image similarity. While we show that ocular aberrations can decrease FFOCT SNR and resolution by up to 14 dB and fivefold, we take advantage of such quantification to discuss different possible compromises between performance gain and adaptive optics complexity and speed, to optimize both sensor-based and sensorless FFOCT high-resolution retinal imaging.
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Frugal random exploration strategy for shape recognition using statistical geometry Hidalgo-Caballero, S., A. Cassinelli, E. Fort, and M. Labousse Physical Review Research 6, no. 2 (2024)
Résumé: Very distinct strategies can be deployed to recognize and characterize an unknown environment or a shape. A recent and promising approach, especially in robotics, is to reduce the complexity of the exploratory units to a minimum. Here, we show that this frugal strategy can be taken to the extreme by exploiting the power of statistical geometry and introducing different invariant features. We show that an elementary robot devoid of any orientation or location system, exploring randomly, can access global information about an environment such as the values of the explored area and perimeter. The explored shapes are of arbitrary geometry and may even nonconnected. From a dictionary, this most simple robot can thus identify various shapes such as famous monuments and even read a text.
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Beyond Order: Random, Aperiodic, and Hyperuniform Photonic Materials: introduction to the special issue Negro, L. D. A. L., C. A. O. Hui, M. Filoche, S. A. Schulz, S. Vignolini, and D. S. Wiersma Optical Materials Express 14, no. 5, 1293-1294 (2024)
Résumé: The editors introduce the feature issue on “Beyond Order: Random, Aperiodic, and Hyperuniform Photonic Materials,” which includes nine articles.
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Topology optimization for microwave control with reconfigurable intelligent metasurfaces in complex media Karamanos, T. D., M. Fink, and F. Lemoult Physical Review Applied 21, no. 4 (2024)
Résumé: Reconfigurable intelligent metasurfaces have been proposed as an efficient solution for improving wireless telecommunication systems in multiple-scattering or reverberating media. Concurrently, topology optimization has been successfully used as an inverse-design technique in many fields, and particularly in electromagnetics. In this work, we apply a gradient-based topology optimization for tuning the binary elements of a metasurface for a focusing goal in a complex environment. First, the metasurface unit cells are approximated as point sources and, then, the optimization problem is formulated. Afterwards, the proposed method is applied to find the optimal parameter sets for three distinct environments of increasing complexity, and the resulting focus for each case is demonstrated via numerical simulations. The combination of a reverberating cavity and a metasurface inside the latter is very powerful since everything can be solved analytically for focusing outside the cavity.
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Asymmetrical wakes over anisotropic bathymetries Euvé, L.-P., A. Maurel, P. Petitjeans, and V. Pagneux Journal of Fluid Mechanics 984 (2024)
Résumé: The study investigates the impact of a vertically layered bathymetry, consisting of submerged vertical plates, on a ship wake through theoretical analysis and experimental realization. For subwavelength distances between the plates, the analysis relies on a homogenized model that provides an effective, anisotropic, dispersion relation for the propagation of water waves. Our findings reveal that a highly asymmetric wake can be achieved, with the degree of asymmetry contingent upon the ship propagation direction in relation to the plate orientation. This anisotropy is characterized with respect to water depth and to ship length using the dimensionless depth and hull Froude numbers. Laboratory experiments align closely with theoretical predictions, confirming that the asymmetry of the wake can indeed be managed through manipulation of bathymetric conditions.
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Airborne ultrasound for the contactless mapping of surface thoracic vibrations during human vocalizations: A pilot study Wintzenrieth, F., M. Couade, F. Lehanneur, P. Laveneziana, M. C. Niérat, N. Verger, M. Fink, T. Similowski, and R. K. Ing AIP Advances 14, no. 3 (2024)
Résumé: Physical examination of the thorax is key to the clinical diagnosis of respiratory diseases. Among other examination techniques, palpation evaluates the transmission of high-frequency vibrations produced by vocalizations (tactile fremitus), which helps the physicians to identify abnormalities within the respiratory system. We propose the use of an airborne ultrasound surface motion camera (AUSMC) to quantitatively map the vibrations induced by subject vocalization. This approach could make the examination of vocal fremitus quantifiable, reproducible, and archivable. Massive data collection of vocal fremitus could allow using artificial intelligence algorithms to isolate vibration patterns that could help disease identification. Until now, in contrast, the interpretation of vocal fremitus has been subject to the physician’s experience and remains subjective. In the present work, we demonstrate the capabilities of the AUSMC to measure vocal fremitus thoracic vibration maps on 77 healthy volunteers. We have observed a spatial dependence of vibration maps on vocalization frequency. We observed that the left lung generates fewer surface vibrations than the right one, which was expected according to their respective dimensions. We also discuss the implications of our findings.
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Multiple scattering theory in one dimensional space and time dependent disorder: average field [Invited] Selvestrel, A., J. Rocha, R. Carminati, and R. Pierrat Optical Materials Express 14, no. 3, 801-815 (2024)
Résumé: We theoretically study the propagation of light in one-dimensional space- and time-dependent disorder. The disorder is described by a fluctuating permittivity ε(x, t) exhibiting short-range correlations in space and time, without cross correlation between them. Depending on the illumination conditions, we show that the intensity of the average field decays exponentially in space or in time, with characteristic length or time defining the scattering mean-free path ℓs and the scattering mean-free time τs. In the weak scattering regime, we provide explicit expressions for ℓs and τs, that are checked against rigorous numerical simulations.
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A simplified PPG based approach for automated recognition of five distinct emotional states Paul, A., A. Chakraborty, D. Sadhukhan, S. Pal, and M. Mitra Multimedia Tools and Applications 83, no. 10, 30697-30718 (2024)
Résumé: Emotion is a complicated state of mind, which normally reflects human perceptions and attitudes. Proper recognition of emotional states and its quality plays crucial role for the detection of critical diseases and subsequent treatment procedures. Generally, multi-lead, complicated Electroencephalogram (EEG) based analysis predominate the characterization of emotion detection. Nowadays, user-friendly, rich-cardiac-information and wearable characteristics of the photoplethysmogram (PPG) signal are also being used to identify the emotional states. However, a majority of the reported emotion detection techniques mostly uses PPG signal in multimodality approach. In this paper, a simple methodology is proposed to identify multiple emotional states via the analysis of the PPG signal alone. Normally, emotion induced alteration in the heart rate causes variation in the blood ejection rate and a subsequent deviation in the balance of the systolic and the diastolic phases. Consequently, a specific time-domain characteristic is identified to quantify such imbalance and its variability is then used as a feature to discriminate between the five most prominent emotional states via a threshold-based classification technique. The algorithm presents superior performance while evaluated on the PPG data collected from the standard DEAP dataset with an average detection accuracy of 97.78%. Compared to existing literatures, the superior results establish the effectiveness of the proposed algorithm for the detection of multiple emotional states using PPG signal only. Moreover, the use of a single PPG feature and the application of a simple threshold-based classification technique also justify its promises for implementation in real-life, healthcare applications.
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Vectorial phase retrieval in super-resolution polarization microscopy Gutiérrez-Cuevas, R., L. A. Alemán-Castañeda, I. Herrera, S. Brasselet, and M. A. Alonso APL Photonics 9, no. 2 (2024)
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Dynamic structured illumination for confocal microscopy Nœtinger, G., F. Lemoult, and S. M. Popoff Optics Letters 49, no. 5, 1177-1180 (2024)
Résumé: Structured illumination enables the tailoring of an imaging device’s optical transfer function to enhance resolution. We propose the incorporation of a temporal periodic modulation, specifically a rotating mask, to encode multiple transfer functions in the temporal domain. This approach is demonstrated using a confocal microscope configuration. At each scanning position, a temporal periodic signal is recorded. By filtering around each harmonic of the rotation frequency, multiple images of the same object can be constructed. The image carried by the nth harmonic is a convolution of the object with a phase vortex of topological charge n, similar to the outcome when using a vortex phase plate as an illumination. This enables the collection of chosen high spatial frequencies from the sample, thereby enhancing the spatial resolution of the confocal microscope.
Mots-clés: wavefront shaping, confocal, microscopy, super-resolution
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Flexible implementation of modulated localisation microscopy based on DMD Illand, A., P. Jouchet, E. Fort, and S. Lévêque-Fort Journal of Microscopy (2024)
Résumé: Localisation microscopy of individual molecules allows one to bypass the diffraction limit, revealing cellular organisation on a nanometric scale. This method, which relies on spatial analysis of the signal emitted by molecules, is often limited to the observation of biological objects at shallow depths, or with very few aberrations. The introduction of a temporal parameter into the localisation process through a time-modulated excitation was recently proposed to address these limitations. This method, called ModLoc, is demonstrated here with an alternative flexible strategy. In this implementation, to encode the time-modulated excitation a digital micromirror device (DMD) is used in combination with a fast demodulation approach, and provides a twofold enhancement in localisation precision. Layout: Nowadays, we can use an optical microscope to observe how proteins are organised in 3D within a cell at the nanoscale. By carefully controlling the emission of molecules in both space and time, we can overcome the limitations set by the diffraction limit. This allows us to pinpoint the exact location of molecules more precisely. However, the usual spatial analysis method limits observations to shallow depths or causing low distortion of optical waves. To overcome these restrictions, a recent approach introduces a temporal element to the localisation process. This involves changing the illumination over time to enhance the precision of localisation. This method, known as ModLoc, is showcased here using a flexible and alternative strategy. In this setup, a matrix of micrometric mirrors, working together with a fast demodulation optical module, is used to encode and decode the time-modulated information. This combination results in a twofold improvement in localisation precision.
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Optimizing multi-user indoor sound communications with acoustic reconfigurable metasurfaces Zhang, H., Q. Wang, M. Fink, and G. Ma Nature Communications 15, no. 1, 1270 (2024)
Résumé: Sound in indoor spaces forms a complex wavefield due to multiple scattering encountered by the sound. Indoor acoustic communication involving multiple sources and receivers thus inevitably suffers from cross-talks. Here, we demonstrate the isolation of acoustic communication channels in a room by wavefield shaping using acoustic reconfigurable metasurfaces (ARMs) controlled by optimization protocols based on communication theories. The ARMs have 200 electrically switchable units, each selectively offering 0 or π phase shifts in the reflected waves. The sound field is reshaped for maximal Shannon capacity and minimal cross-talk simultaneously. We demonstrate diverse acoustic functionalities over a spectrum much larger than the coherence bandwidth of the room, including multi-channel, multi-spectral channel isolations, and frequency-multiplexed acoustic communication. Our work shows that wavefield shaping in complex media can offer new strategies for future acoustic engineering.
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Characterization of ejecta in shock experiments with multiple light scattering Don Jayamanne, J. A., J. R. Burie, O. Durand, R. Pierrat, and R. Carminati Journal of Applied Physics 135, no. 7 (2024)
Résumé: Upon impact, the free surface of a solid metal may eject a cloud of fast and fine particles. Photon Doppler Velocimetry (PDV) is one of the optical diagnostics used to characterize these ejecta. Although the technique provides a direct way to estimate the particle velocities in the single scattering regime, it has been shown that multiple scattering cannot be neglected in real ejecta. Here, we derive a model for PDV measurements starting from the first principles of wave scattering. We establish rigorously the relationship between the specific intensity and the measured signal, as well as the Radiative Transport Equation (RTE) that describes the evolution of the specific intensity upon scattering and absorption in dynamic ejecta, including the effects of inelastic scattering and inhomogeneities in the optical properties. We also establish rigorously the connection between the Monte Carlo scheme used for numerical simulations and the solution to the RTE. Using numerical simulations, we demonstrate the crucial contribution of multiple scattering to PDV spectrograms as well as the effect of statistical inhomogeneities in particle size distribution. These results could substantially impact the analysis of ejecta by PDV.
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Acoustic monitoring of compaction in cohesive granular materials Canel, V., X. Jia, M. Campillo, and I. Ionescu Physical Review E 109, no. 2 (2024)
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Viscoelastic dynamics of a soft strip subject to a large deformation Delory, A., D. A. Kiefer, M. Lanoy, A. Eddi, Prada C., and F. Lemoult Soft Matter (2024)
Résumé: To produce sounds, we adjust the tension of our vocal folds to shape their properties and control the pitch. This efficient mechanism offers inspiration for designing reconfigurable materials and adaptable soft robots. However, understanding how flexible structures respond to a significant static strain is not straightforward. This complexity also limits the precision of medical imaging when applied to tensioned organs like muscles, tendons, ligaments and blood vessels among others. In this article, we experimentally and theoretically explore the dynamics of a soft strip subject to a substantial static
extension, up to 180%. Our observations reveal a few intriguing effects, such as the resilience of certain vibrational modes to a static deformation. These observations are supported by a model based on the incremental displacement theory. This has promising practical implications for characterizing soft materials but also for scenarios where external actions can be used to tune properties.
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Experimental Investigation of the Thermal Emission Cross Section of Nanoresonators Using Hierarchical Poisson-Disk Distributions Langevin, D., C. Verlhac, J. Jaeck, L. Abou-Hamdan, E. Taupeau, B. Fix, N. Bardou, C. Dupuis, Y. De Wilde, R. Haïdar, and P. Bouchon Physical Review Letters 132, no. 4 (2024)
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Efficient detection of cardiac abnormalities via a simplified score-based analysis of the ECG signal Dhar, S., A. Chakraborty, D. Sadhukhan, S. Pal, and M. Mitra Journal of Ambient Intelligence and Humanized Computing (2024)
Résumé: Nowadays, automated analysis of the electrocardiogram (ECG) signal is a popular choice to facilitates easy and expert-independent detection of lethal cardiovascular diseases (CVDs). Although, a majority of the state-of-the-art algorithms are found to be lagging due to the use of complicated methodologies, limited dataset, high feature dimension, feature selection or intense classification techniques. In this research an original, easy-to-use ECG based methodology is proposed for completely automated identification of multiple types of critical CVDs. Primarily, after preprocessing the algorithm uses a simplified technique for exact detection of ECG fiducial points. Then, based on detected fiducial points, some well interpretable and prominent ECG time domain features are efficiently extracted and a binary feature matrix has been derived using those features from different leads. Finally, a distinctive score is evaluated from the binary feature matrix calculating the sum of weighted feature value and only by utilizing the score,discrimination between the various types of CVDs is highly detectable. Proficiency of the algorithm is widely evaluated on the 12-lead ECG signal data collected from Physikalisch-Technische-Bundesanstalt (PTB) and PTB-XL database. The algorithm presents promising outcome with average accuracy, sensitivity and specificity of 99.43%, 98.27% and 99.59%, respectively. Evidently, the algorithm is capable enough and efficient as well in comparison with other reported techniques till date. Moreover, the use of a unique score derived from the binary matrix ascertains the exact detection of multiple cardiac abnormalities and the superior classification accuracy makes the algorithm promising for personal computerized health monitoring applications.
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Ray and caustic structure of Ince-Gauss beams Gutiérrez-Cuevas, R., M. R. Dennis, and M. A. Alonso New Journal of Physics 26, no. 1 (2024)
Résumé: The Ince-Gauss beams, separable in elliptic coordinates, are studied through a ray-optical approach. Their ray structure can be represented over a Poincaré sphere by generalized Viviani curves (intersections of a cylinder and a sphere). This representation shows two topologically different regimes, in which the curve is composed of one or two loops. The overall beam shape is described by the ray caustics that delimit the beams’ bright regions. These caustics are inferred from the generalized Viviani curve through a geometric procedure that reveals connections with other physical systems and geometrical constructions. Depending on the regime, the caustics are composed either of two confocal ellipses or of segments of an ellipse and a hyperbola that are confocal. The weighting of the rays is shown to follow the two-mode meanfield Gross-Pitaevskii equations, which can be mapped to the equation of a simple pendulum. Finally, it is shown that the wave field can be accurately estimated from the ray description.
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3D-Architected Alkaline-Earth Perovskites Winczewski, J. P., J. Arriaga Dávila, M. Herrera-Zaldívar, F. Ruiz-Zepeda, R. M. Córdova-Castr, C. R. Pérez De La Vega, C. Cabriel, I. Izeddin, H. Gardeniers, and A. Susarrey-Arce Advanced Materials (2024)
Résumé: 3D ceramic architectures are captivating geometrical features with an immense demand in optics. In this work, an additive manufacturing (AM) approach for printing alkaline-earth perovskite 3D microarchitectures is developed. The approach enables custom-made photoresists suited for two-photon lithography, permitting the production of alkaline-earth perovskite (BaZrO3, CaZrO3, and SrZrO3) 3D structures shaped in the form of octet-truss lattices, gyroids, or inspired architectures like sodalite zeolite, and C60 buckyballs with micrometric and nanometric feature sizes. Alkaline-earth perovskite morphological, structural, and chemical characteristics are studied. The optical properties of such perovskite architectures are investigated using cathodoluminescence and wide-field photoluminescence emission to estimate the lifetime rate and defects in BaZrO3, CaZrO3, and SrZrO3. From a broad perspective, this AM methodology facilitates the production of 3D-structured mixed oxides. These findings are the first steps toward dimensionally refined high-refractive-index ceramics for micro-optics and other terrains like (photo/electro)catalysis.
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Single-emitter super-resolved imaging of radiative decay rate enhancement in dielectric gap nanoantennas Córdova-Castro, R. M., B. Van Dam, A. Lauri, S. A. Maier, R. Sapienza, Y. De Wilde, I. Izeddin, and V. Krachmalnicoff Light: Science and Applications 13, no. 1 (2024)
Résumé: High refractive index dielectric nanoantennas strongly modify the decay rate via the Purcell effect through the design of radiative channels. Due to their dielectric nature, the field is mainly confined inside the nanostructure and in the gap, which is hard to probe with scanning probe techniques. Here we use single-molecule fluorescence lifetime imaging microscopy (smFLIM) to map the decay rate enhancement in dielectric GaP nanoantenna dimers with a median localization precision of 14 nm. We measure, in the gap of the nanoantenna, decay rates that are almost 30 times larger than on a glass substrate. By comparing experimental results with numerical simulations we show that this large enhancement is essentially radiative, contrary to the case of plasmonic nanoantennas, and therefore has great potential for applications such as quantum optics and biosensing.
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3D topographies promote macrophage M2d-Subset differentiation Carrara, S. C., A. Davila-Lezama, C. Cabriel, E. J. W. Berenschot, S. Krol, J. G. E. Gardeniers, I. Izeddin, H. Kolmar, and A. Susarrey-Arce Materials Today Bio 24 (2024)
Résumé: In vitro cellular models denote a crucial part of drug discovery programs as they aid in identifying successful drug candidates based on their initial efficacy and potency. While tremendous headway has been achieved in improving 2D and 3D culture techniques, there is still a need for physiologically relevant systems that can mimic or alter cellular responses without the addition of external biochemical stimuli. A way forward to alter cellular responses is using physical cues, like 3D topographical inorganic substrates, to differentiate macrophage-like cells. Herein, protein secretion and gene expression markers for various macrophage subsets cultivated on a 3D topographical substrate are investigated. The results show that macrophages differentiate into anti-inflammatory M2-type macrophages, secreting increased IL-10 levels compared to the controls. Remarkably, these macrophage cells are differentiated into the M2d subset, making up the main component of tumour-associated macrophages (TAMs), as measured by upregulated Il-10 and Vegf mRNA. M2d subset differentiation is attributed to the topographical substrates with 3D fractal-like geometries arrayed over the surface, else primarily achieved by tumour-associated factors in vivo. From a broad perspective, this work paves the way for implementing 3D topographical inorganic surfaces for drug discovery programs, harnessing the advantages of in vitro assays without external stimulation and allowing the rapid characterisation of therapeutic modalities in physiologically relevant environments.
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Optical tomography in a single camera frame using fringe-encoded deep-learning full-field OCT Mazlin, V. Biomedical Optics Express 15, no. 1, 222-236 (2024)
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Decomposition of acousto-elastic matrices for contactless modal analysis and vibration shaping Palerm, C., C. Prada, B. Gerardin, A. Talon, and J. De Rosny Journal of Sound and Vibration 571 (2024)
Résumé: A contactless method based on acousto-elastic transmission matrix analysis is proposed to recover the modal properties of weakly damped mechanical structures. The matrix is acquired using eight loudspeakers and a laser vibrometer probing hundreds of points. The matrix analysis is particularly interesting in case of overlapping modes. The proposed measurement set-up and associated data processing using the Singular Value Decomposition are applied to two symmetric samples, a gear and two monobloc impellers. Further analysis are performed taking advantage of their particular modal behavior, common to many rotationally symmetric structures. The method also enables to clearly identify the effect of damages on the modal organization. Additionally, the setup can also be used to excite specific patterns on the elastic structures. Finally, the acousto-elastic results are compared to the ones obtained with a classical impact hammer and high resolution algorithms.
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