Search

Screening of unknown particles, including viruses and nanoparticles, is key in medicine, industry and pollutant determination. However, existing techniques require sample a priori knowledge or modification (e.g. fluorescence). Here we introduce RYtov MIcroscopy for Nanoparticles Identification (RYMINI), a noninvasive and non-destructive optical approach that is combining holographic labelfree 3D tracking and high-sensitivity quantitative phase imaging into a compact optical setup. Dedicated to the characterization of nano-objects in solution, it is compatible with highly demanding environments such as level-3 biological laboratories. Metrological characterization has been performed at the level of each single object on both absorbing and transparent particles as well as on infectious HIV-1, SARS-CoV-2 and extracellular vesicles in solution. We demonstrate the capability of RYMINI to determine the nature, concentration, size, complex refractive index and mass of each single particle. We discuss the application of the method in unknown solution without requiring any knowledge or model of the particles’ response. It paves the way to label-free nano-object identification in terra incognita., Le criblage de particules inconnues, y compris les virus et les nanoparticules, est essentiel dans la médecine, l'industrie et la détermination des polluants. Cependant, les techniques existantes nécessitent une connaissance ou une modification a priori de l'échantillon (par exemple, la fluorescence). Nous présentons ici RYtov MIcroscopy for Nanoparticles Identification (RYMINI), une approche optique non invasive et non destructive qui combine le suivi 3D holographique sans marquage et l'imagerie de phase quantitative à haute sensibilité dans une configuration optique compacte. Dédié à la caractérisation de nano-objets en solution, il est compatible avec des environnements très exigeants tels que les laboratoires biologiques de niveau 3. La caractérisation métrologique a été réalisée au niveau de chaque objet sur des particules absorbantes et transparentes ainsi que sur des particules infectieuses (VIH-1, SARS-CoV-2) et des vésicules extracellulaires en solution. Nous démontrons la capacité de RYMINI à déterminer la nature, la concentration, la taille, l'indice de réfraction complexe et la masse de chaque particule. Nous discutons de l'application de la méthode en solution inconnue sans nécessiter connaissance ou modèle a priori de la réponse des particules. Cela ouvre la voie à une identification sans étiquette des nano-objets en terra incognita.

We describe the vibration pattern of a soliton-molecule using the Langevin’s model, i.e. noise source combined with a deterministic model. This simpler model allows investigating the interplay between fl uctuation and dissipation mechanisms at play.

The study of temporal solitons has revolutionized fiber optics, yielded new classes of ultrafast laser and opened multiple interdisciplinary applications.

We review our recent work on the dynamics of breathing solitons in fibre lasers, including single breathers, breather molecular complexes, breather explosions and breather frequency locking at Farey fractions, and their control by genetic algorithms.

We deploy a neural network to predict the spectro-temporal evolution of a periodic waveform upon nonlinear fibre propagation and demonstrate efficient probing of the input-parameter space for on-demand comb generation or significant spectral/temporal focusing occurrence.

International audience; We study the potential of the commercial mounting medium Slowfade diamond as a buffer for STORM microscopy. We show that although it does not work with the popular far-red dyes typically used for STORM imaging, such as Alexa Fluor 647, it performs really well with a wide variety of green-excited dyes such as Alexa Fluor 532, Alexa Fluor 555 or CF 568. Moreover, imaging can be performed several months after the samples are mounted in this environment and kept in the fridge, providing a convenient way to preserve samples for STORM imaging, as well as to keep calibration samples, for example for metrology or teaching in particular in imaging facilities.

We study the dynamic surface response of neolithic stone settlements obtained with seismic ambient noise techniques near the city of Carnac in French Brittany. Surprisingly, we find that menhirs (neolithic human size standing alone granite stones) with an aspect ratio between 1 and 2 periodically arranged atop a thin layer of sandy soil laid on a granite bedrock, exhibit fundamental resonances in the range of 10 to 25 Hz. We propose an analogic Kelvin-Voigt viscoelastic model that explains the origin of such low frequency resonances. We further explore low frequency filtering effect with full wave finite element simulations. Our numerical results confirm the bending nature of fundamental resonances of the menhirs and further suggest additional resonances of rotational and longitudinal nature in the frequency range 25 to 50 Hz. Our study thus paves the way for large scale seismic metasurfaces consisting of granite stones periodically arranged atop a thin layer of regolith over a bedrock, for ground vibration mitigation in earthquake engineering., 6 pages, 7 figures

International audience; Optical metasurfaces are becoming ubiquitous optical components to mold the amplitude, the phase and the polarization properties of light beams. So far, most of these devices are passive in essence, that is, they cannot be arbitrarily reconfigured or optimized according to the user's interest and/or change in their surrounding environment. Here we propose an innovative design strategy relying on the position of topological singularities, namely zeros and poles of the reflection coefficient, to address full phase modulation of light reflecting off an active metasurface with almost unity efficiency. The active metasurface unit cells, consisting of asymmetric Gires-Tournois resonators filled with electro-optics materials comprising either of Liquid crystal or multiple quantum wells, are able to modulate the reflected field from 0 to 2π associated with 100% reflection amplitude despite dealing with extremely low refractive index change on the order of 0.01. The second ingredient to achieve high efficiency modulation consists in optimizing the arrangement of the sub-wavelength unit-cells so as to account for local imperfection and near-field coupling between neighboring structures. Consequently, an advanced optimization method accompanied with high-fidelity full-wave solver are required to identify the refractive index distribution. In our case we rely on a statistical learning optimization technique. It is based on a surrogate model representation which provides a quick estimation to approximate the true function of interest to select the best candidates for the next simulation. Accordingly, programable beam steering configurations have been designed with ultimate performance in reflection. The realization of active beam splitter and active beam steering devices operating at GHz deflection frequency would open important applications in imaging microscopy, high resolution image projection, optical communication and 3D light detection and ranging (LiDAR).

High harmonic generation in condensed media has been an emerging field since its first observation in 2011. The strong dependency of the harmonics on the crystal band structure and laser parameters make them an excellent observable of the fundamental mechanisms of generation. Moreover, the compact configuration of the source combined with the possibility for structuring the generation medium makes it a promising source of extreme ultraviolet radiation for e.g. spectroscopy or imaging applications. In this thesis, we investigate three different aspects of the high harmonic generation in crystals. First, doping that induces changes of the band structure and its effect on the emission process. The two example systems for this are chromium doped magnesium oxide and gallium implanted silicon, for which the doping leads to an enhancement of the harmonic yield. After, we show that by using a coherent diffraction imaging technique, it is possible to image nanostructures solely based on the harmonics emitted by the structure itself. Because surface nanostructuring is emerging as a way of inducing complex properties directly into the harmonic beam, such as an orbital angular momentum, this opens up the possibility of in-situ characterization of these structures. Finally, the concept of polarization gating used in gases is adapted for solids by using the strong anisotropic harmonic response. It is used in order to temporally shape the emission and push towards isolated attosecond pulse generation., La génération d'harmoniques d'ordre élevées dans les milieux condensés est un domaine émergent depuis sa première observation en 2011. La forte dépendance des harmoniques à la structure de bande cristalline et aux paramètres laser en fait une excellente observable des mécanismes fondamentaux de génération. De plus, la configuration compacte de la source combinée à la possibilité de structurer le milieu de génération en fait une source prometteuse de rayonnement extrême ultraviolet pour, par exemple, des applications de spectroscopie ou d'imagerie. Dans cette thèse, nous étudions trois caractéristiques de la génération d'harmoniques dans les cristaux. Premièrement, l'effet des changements de structure de bande induits par le dopage sur le processus d'émission. Les deux exemples de systèmes sont l'oxyde de magnésium dopé au chrome et le silicium implanté au gallium, pour lesquels le dopage conduit à une amélioration du rendement de génération. Ensuite, nous montrons qu'en utilisant une technique d'imagerie par diffraction cohérente, il est possible d'imager des nanostructures uniquement en se basant sur les harmoniques émises par la structure elle-même. Parce que la nanostructuration de surface émerge comme un moyen d'induire des propriétés complexes directement dans le faisceau harmonique, comme un moment angulaire orbital, cela ouvre la possibilité d'une caractérisation in-situ de ces structures. Enfin, le concept de porte de polarisation utilisé dans les gaz est adapté pour les solides en utilisant la forte réponse anisotrope des harmoniques. C'est utilisé pour façonner temporellement l'émission et permettre la génération d'impulsions attosecondes isolées.

Reflection high-energy electron diffraction (RHEED) is a powerful tool in molecular beam epitaxy (MBE), but RHEED images are often difficult to interpret, requiring experienced operators. We present an approach for automated surveillance of GaAs substrate deoxidation in MBE reactors using deep learning based RHEED image-sequence classification. Our approach consists of an non-supervised auto-encoder (AE) for feature extraction, combined with a supervised convolutional classifier network. We demonstrate that our lightweight network model can accurately identify the exact deoxidation moment. Furthermore we show that the approach is very robust and allows accurate deoxidation detection during months without requiring re-training. The main advantage of the approach is that it can be applied to raw RHEED images without requiring further information such as the rotation angle, temperature, etc., 8 pages, 5 figures

International audience

Ultrafast imaging is essential in physics and chemistry to investigate the femtosecond dynamics of nonuniform samples or of phenomena with strong spatial variations. It relies on observing the phenomena induced by an ultrashort laser pump pulse using an ultrashort probe pulse at a later time. Recent years have seen the emergence of very successful ultrafast imaging techniques of single non-reproducible events with extremely high frame rate, based on wavelength or spatial frequency encoding. However, further progress in ultrafast imaging towards high spatial resolution is hampered by the lack of characterization of weak probe beams. For pump–probe experiments realized within solids or liquids, because of the difference in group velocities between pump and probe, the determination of the absolute pump–probe delay depends on the sample position. In addition, pulse-front tilt is a widespread issue, unacceptable for ultrafast imaging, but which is conventionally very difficult to evaluate for the low-intensity probe pulses. Here we show that a pump-induced micro-grating generated from the electronic Kerr effect provides a detailed in-situ characterization of a weak probe pulse. It allows solving the two issues of absolute pump–probe delay determination and pulse-front tilt detection. Our approach is valid whatever the transparent medium with non-negligible Kerr index, whatever the probe pulse polarization and wavelength. Because it is nondestructive and fast to perform, this in-situ probe diagnostic can be repeated to calibrate experimental conditions, particularly in the case where complex wavelength, spatial frequency or polarization encoding is used. We anticipate that this technique will enable previously inaccessible spatiotemporal imaging in a number of fields of ultrafast science at the micro- and nanoscale., The article reports a technique to characterize, inside a sample, ultrafast probe pulses with weak intensity: zero delay, optimal compression, pulse front tilt. The measurement is non-destructive, valid for all wavelengths and polarizations.

International audience

National audience

International audience

Recently, a variety of unrolled networks have been proposed for image reconstruction. These can be interpreted as parameter-optimized algorithms that incorporate steps that are traditionally encountered during the optimization of a hand-crafted objective or in the Bayesian formulation. Here, we address the problem of training such networks in the presence of signal-dependent noise, which is more realistic that the common additive Gaussian noise; however, it is also much more computationally demanding, when possible. In particular, we focus on the deep expectation-maximization network and describe how to approximate the Bayesian denoised completion step to reduce the computational cost and memory requirements while limiting the reconstruction error. We present reconstruction results from simulated data at different noise levels. Our network yields higher reconstruction peak signal-to-noise ratios than other similar approaches. In particular, our network shows greater robustness in the practical case where the noise level is unknown or is badly estimated.

The development of solar concentrator technology has just reached a very significant level. Using reflectors to concentrate the sun's rays on the absorber dramatically reduces the size of the absorber, reducing heat loss and increasing its efficiency at high temperatures. Another advantage of this system is that the reflectors are significantly less expensive, per unit area, than the flat collectors. To determine the performances of a cylindrical-parabolic concentrator, mathematical modeling of the heat balance on the absorber, the coolant, and the glass envelope was established using Matlab. The system of equations obtained is solved by the finite difference method. The results for a typical day are the variation in the temperature of the heat transfer fluid, the absorber tube, and the glass envelope. Thus, we examine the effect of the wind speed, flow rate on the temperature distribution of the coolant at the outlet. However, for a mass flow rate of the fluid of 0.1 kg / s, the outlet temperature of the fluid is 85 ° C with a thermal efficiency of 73%. Excluding the energy absorbed by the absorber tube is 75% of the solar intensity received on the reflector. Keywords: Parabolic trough collector, Solar thermal energy, Simulation, Heat transfer, Solar concentrator

International audience

International audience; Direct bonding has been a major key technology in many fields nowadays. From microelectronic to optoelectronic technologies, it became a technique used for mass production technology in many different applications. Direct bonding of silicon or silicon dioxide is now a well known process. In this article, we explore this technology through the transfer of III-V AlGaAs/GaAs crystalline multilayer from its native GaAs substrate upon a fused silica substrate (SiO2). The goal of this work is to explore the conception of crystalline Bragg mirrors with low mechanical loss and high optical quality for precision measurement applications.We present the main results obtained for each step of the transfer process. Various experiment such as AFM characterization have been performed on the wafers to probe surface quality. Chemical wet etching with different experimental conditions have been tested to remove the GaAs substrate. We discuss the main challenges of the process, especially the bonding of two rather different materials from the thermo-mechanic point of view. Focus is also made on the chemistry used in the wet etching part to have a selective etching between GaAs and AlGaAs.

A new application for a laser-cooled trapped ion ensemble is proposed for the non-destructive detection of giant molecules. In this application a molecular ion is injected into a Ca+ ion ensemble. The detection signal is expected in the fluorescence of the ion set which may vary after the perturbation induced by the molecule. In this manuscript, the necessary elements for the design and handling of a prototype are presented, as well as experimental and numerical results to validate the concept and to study the operating conditions. The thesis is organised in three parts. The first part presents the fundamental aspects of ion trapping and laser cooling, with an emphasis on the non-adiabatic case the behaviour of more than one ions. Experimental principles and results are also exhibited. The second part deals with the fundamental and experimental aspects of the electrospray ionisation molecular source and its attached guiding elements for charged particle. This part is the opportunity to sum up the recent advances in similar systems. The third part presents the molecular dynamics simulations conducted in order to numerically reproduce the interaction as well as to study the behaviour of the trapped ions. With the simulations, we highlight the key roles of the Coulomb interaction combined with radio-frequency heating in the cloud destabilisation mechanism leading to detection. The conditions favouring detection are studied, as well as certain aspects of ion trapping such as radio-frequency heating., Une nouvelle application pour un ensemble d’ions piégés refroidis par laser est proposée pour la détection non-destructive de molécules géantes. Dans cette application, un ion moléculaire est injecté dans un ensemble d’ions Ca+. Le signal de détection est attendu dans la fluorescence de l’ensemble d’ions susceptible de varier après la perturbation induite par la molécule. Dans ce manuscrit, les éléments nécessaires à la conception, la réalisation et le maniement d’un prototype sont présentés, ainsi que les résultats expérimentaux et numériques permettant de valider le concept et d’étudier les conditions de fonctionnement. La thèse est organisée en trois parties. La première partie présente les aspects fondamentaux du piégeage des ions et de leur refroidissement par laser, en mettant l’accent sur le cas non-adiabatique et le comportement de plusieurs ions. Les principes et résultats expérimentaux sont également exposés. La deuxième partie traite des aspects fondamentaux et expérimentaux de la source moléculaire d’ionisation par électrospray ainsi que des éléments de guidage des particules chargées qui lui sont rattachés. Cette partie est l’occasion de faire le point sur les avancées récentes dans des systèmes similaires. La troisième partie présente les simulations de dynamique moléculaire réalisées afin de reproduire numériquement l’interaction ainsi que d’étudier le comportement des ions piégés. Grâce aux simulations, nous mettons en évidence les rôles clés de l’interaction coulombienne combinée au chauffage radiofréquence dans le mécanisme de déstabilisation du nuage conduisant à la détection. Les conditions favorisant la détection sont étudiées, ainsi que certains aspects du piégeage des ions comme le chauffage par radiofréquence.

Many optical systems use acousto-optics for fast steering of light. However, acousto-optic (AO) light diffraction permits manipulation and shaping of light fields in a much broader sense including holography. While acousto-optic devices operate at incontestable speed, they are one dimensional (1D) diffraction devices depending on analog serial data transfer and as such have a mode of use distinguished from common 2D spatial light modulators. Combination with an amplified laser source allows to clock the serial buildup of AO diffraction patterns for avoidance of phase aberration in the output beam due to acoustic wave progression. Pseudo 2D holography is established with two crossed AO deflectors for biaxial spatial modulation of the input phase, and optionally also of its amplitude. In this configuration, acousto-optics permits light patterning into micrometer-scale 2D point grids with the possibility to switch the pattern between individual laser pulses. We describe algorithms for deriving AO holograms for either pure phase modulation or for a co-modulation of amplitude. Computationally reconstructed phase holograms show focal patterns in presence of side lobes. Side lobes are entirely suppressed by amplitude modulation, though at the expense of reduced optical power transmission., under review with JPhys Photonics

International audience; The 3D orientation of a single gold nano-bipyramid (AuBPs) on a glass substrate is successfully measured by polarimetric analysis of its scattering. The AuBPs are very attractive due to the presence of hot spots at their end tips resulting from a strong longitudinal localized surface plasmon resonance. In addition, this resonance can be modeled as a radiating dipole. To study the 3D orientation, we designed a specific spectroscopic dark-field microscope with a precise control of the collection angles of the scattering in the Fourier plane. The 3D angles are resolved by analyzing the polarization of the AuBP scattering. Simulations are used to extract the inplane and out-of-plane angles with a very good accuracy of 3 %. In particular, the critical role of the numerical aperture collection was investigated experimentally by Fourier filtering of the scattering into the back focal plane of the objective. It reveals a physical insight into the contribution of the evanescence waves and provides a technical guideline for choosing the collection objective for polarimetric measurements.

International audience; We introduce a nano-optical platform based on Bloch surface waves (BSWs) capable of exploiting the entire cleaved end facet of a multicore optical fiber. Interconnecting various fiber cores with BSWs directly at the end of a multicore fiber opens the perspective of highly compact complex optical functionalities for the design of “lab on fiber” devices. In counterpart, optical fibers provide a unique opportunity to obtain turnkey nano-optical functions addressing a vast application domain ranging from telecommunications to medical sensing. To show the full potential of our platform, we demonstrate a multiplexing function between three fiber cores.

International audience; Optical characterization and appearance prediction of translucent materials is needed in several fields of engineering such as computer graphics, dental restorations or 3D printing technologies. In the case of strongly diffusing materials, flux transfer models like the Kubelka-Munk model (2-flux) or 4-flux model have been successfully used to this aim for decades. However, they lead to inaccurate prediction of the color variations of translucent objects of different thicknesses. Indeed, as they assume Lambertian fluxes at any depth within the material and in particular at the bordering interfaces, they fail to model the internal reflectance at the interfaces, penalizing the accuracy of the optical parameter extraction. The aim of the paper is to investigate the impact of translucency on light angular distribution and corresponding internal reflectances, by the mean of the radiative transfer equation, which describes more rigorously the impact of the scattering on the light propagation. It turns out that the light angular distribution at the bordering interfaces, assumed to be flat, is far from being Lambertian, and the internal reflectance may vary a lot according to the layer's thickness, refractive index, scattering and absorption coefficients. This work not only enables to better understand the impact of scattering within a translucent layer but also invites to revisit the well-known Saunderson correction used in 2-or 4-flux models.

Street lighting ensures visibility and legibility for road users. In this paper, performances of the lighting installation of two road sections with different type of road surface are measured in accordance with guidelines and road lighting standards. Then, the calculation of the visibility level of a target according to the Adrian’s model is included considering the light reflections on the road. We compare the results obtained for each section with and without considering the light reflections and conclude that there is an incidence of the nature of the road surface on the target luminance. However, the effect on the visibility level of the target is not so straightforward. This depends on whether it is close to the visibility threshold, and it is therefore important to consider the reflective properties of the road surface. Moreover, we see that the visibility level provides us more information than the classical descriptors. The same luminance distribution for two pavement/lighting couples does not necessarily lead to the same distribution in terms of target visibility. It seems necessary to us to reinstate the visibility level in the performance criteria defined by the standard because it would act as a local descriptor of the performance of the pavement/lighting combination and would thus make it possible to avoid safety problems.

Microcavity polaritons originate from the strong coupling between cavity photons and electronic excitations of a semiconductor microcavity. These quasi-particles inherit properties from both constituents: the electronic component is responsible for giant Kerr non-linearities while the photonic part makes the system inherently dissipative and allows confining polaritons in micro-structures obtained via etching of the cavity. This thesis presents the study of the non-linear properties of micro-cavity arrays with chiral symmetry. The first part of the work is dedicated to one-dimensional topological lattices emulating the Su-Schrieffer-Heeger model. In the non-linear regime, driving the system coherently using a laser leads to the formation of gap solitons at the edges and in the bulk of the structure. We evidenced that such solitons present symmetry properties making them robust against certain types of defects. In addition, we unveiled that a careful engineering of the drive allows observing novel non-linear solutions which are specific to open systems. We analyzed the systems excitations spectrum in presence of such stationary state and demonstrate the possibility to realize a topological phase transition induce by the interactions. In the second part, we explored the properties of the interaction between two gap solitons and showed that the interaction sign is strongly linked to the underlying structure of the lattice. This work showed the presence of a spontaneous symmetry breaking. The study of the systems non-linear response in the vicinity of such phase allows us to discover a novel effect of bistability allowing to induce chirality in the system depending on the drive protocol. We called this effect “helical bistability”. The helical bistability is a very general effect that can be observed in a simple set of two coupled Kerr resonators and is linked to the physics of a particle with spin one half. These results are supported both by numerical simulations and experiments. This thesis illustrates how symmetries and non-linearities enriches the physics of photonic systems in a driven-dissipative context., Les polaritons d'excitons sont des particules mixtes lumière-matière émergeant du couplage fort entre photons de cavité et excitations électroniques dans des microcavités semi-conductrices. Ces quasi-particules héritent des propriétés de leurs deux constituants élémentaires : la composante électronique leur confère une non-linéarité Kerr géante, tandis que la partie photonique rend le système intrinsèquement dissipatif et permet de confiner les polaritons dans des microstructures obtenues en gravant la cavité. Cette thèse présente l'étude des propriétés non-linéaires de réseaux de microcavités optiques présentant la symétrie chirale. La première partie de l'étude est consacrée à des chaînes topologiques unidimensionnelles émulant le modèle de Su-Schrieffer-Heeger. Dans le régime non-linéaire, le pompage cohérent du système en utilisant un laser conduit à la formation de solitons de gap dans le réseau massif ainsi qu'aux bords du réseau. Ces solitons possèdent des propriétés de symétrie qui les rendent robustes face à certains types défauts. D'autre part, en structurant la phase du laser de pompe, de nouvelles solutions non-linéaires apparaissent, qui sont spécifiques à la physique des systèmes ouverts. En présence d'un tel état stationnaire, l'analyse détaillée du spectre des excitations permet de mettre en évidence une transition de phase topologique induite par les interactions. Dans un second temps, l'étude de l'interaction entre deux solitons a permis de montrer que le signe de cette interaction est étroitement lié à la structure du réseau sous-jacent. Ces travaux ont mis en évidence la présence d'une brisure spontanée de symétrie entre les deux solitons. Au voisinage de cette phase, un nouvel effet de multi-stabilité a été découvert, qui permet d'induire de la chiralité dans la réponse du système en fonction du protocole de pompage. Nous dénommons cet effet “bistabilité hélicoïdale”. Cet effet très général peut être obtenu dans un simple système de deux résonateurs non-linéaires couplés, et relié ainsi à la physique d'une particule de spin demi-entier. Ces résultats sont étayés à la fois par des simulations numériques détaillées ainsi que par des expériences. Cette thèse illustre ainsi comment symétries et nonlinéarités permettent d'enrichir considérablement la physique des systèmes photoniques.

International audience; The limiting amplitude principle is a well-known result connecting the solution of the Helmholtzequation with the large-time behavior of timedependent wave equations with a source term which is periodic in time. Motivated by numerical analysis of time-domain methods for stationary scattering problems in heterogeneous media, we quantify the solution convergence of such time-dependent wave equation towards the stationary solution, under some assumptions on the coefficients and the source term. We also generalise the formulation of the limiting amplitude principle to the one-dimensional setting where the classical statement of the principle is known to be violated.

In this contribution, we investigate a simple and reconfigurable all-fiber ring cavity to generate tunable Kerr optical frequency combs in both 1.55-and 2-µm spectral bands. We demonstrate that coherent frequency combs can be obtained by finely exploiting both stimulated Brillouin backscattering and cascaded four-wave mixing in the nonlinear fiber cavity.

The invention relates to a system (10) for characterising a pulse (I) of electromagnetic radiation by time-resolved optical windowing, which comprises an device (1) for forming an interference which is suitable for superimposing four parts of the pulse. The system also comprises a matrix image sensor (3) which selectively captures an interference pattern formed by the pulse from two-photon absorptions. Said system allows the pulse shape to be obtained completely and accurately, and is particularly suitable for characterising ultrashort pulses. In various embodiments, the two-photon absorption can be produced in the matrix image sensor, or replaced by optical frequency doubling which is produced by an SHG crystal plate., Un système (10) de caractérisation d'une impulsion (I) de rayonnement électromagnétique par fenêtrage optique résolu en temps, comprend un dispositif (1) de formation d'une interférence qui est adapté pour superposer quatre parties de l'impulsion. Le système comprend aussi un capteur d'images matriciel (3) qui saisit sélectivement à partir d'absorptions à deux photons, une figure d'interférence formée par l'impulsion. Ledit système permet d'obtenir de façon complète et exacte la forme de l'impulsion, et est particulièrement adapté pour caractériser des impulsions ultracourtes. Dans divers modes de réalisation, l'absorption à deux photons peut être produite dans le capteur d'images matriciel, ou bien remplacée par un doublement de fréquence optique qui est produit par une lame de cristal SHG.

International audience; Inelastic electron tunneling in a scanning tunneling microscope is used to generate excitons in monolayer tungsten disulfide (WS2). Excitonic electroluminescence is measured both at positive and negative sample bias. Using optical spectroscopy and Fourier-space optical microscopy, we show that the bias polarity of the tunnel junction determines the spectral and angular distribution of the emitted light. At positive sample bias, only emission from excitonic species featuring an in-plane transition dipole moment is detected. Based on the spectral distribution of the emitted light, we infer that the dominant contribution is from charged excitons, i.e., trions. At negative sample bias, additional contributions from lower-energy excitonic species are evidenced in the emission spectra and the angular distribution of the emitted light reveals a mixed character of in-plane and out-of-plane transition dipole moments.

Lanthanide-doped nanoparticles constitute a versatile family of photoluminescent local nanoprobes. In this work, we study the photoluminescence of Eu3+-doped NaYF4 nanorods characterized by highly polarized spectra. We develop a full theoretical model and paraxial approximation for nanorod dipole emission. We measure the photoluminescence of individual nanorods by fluorescence confocal microscopy and determine some of their intrinsic optical properties. We also determine the nature (electric or magnetic) and orientations of dipoles moments of the optical transitions used for nanoprobing in the visible range.In addition to the full theoretical model and the paraxial approximation, Fourier microscopy provides a third method to determine the dipole moment angle and but also gives access to the efective height of the nanorods. We also clarify the role of the electric and magnetic transition, including Stark sublevels in the formation of the Fourier plane images, in contrast to the literature.Finally, we use the nanorods as probes for the local density of optical states by performing a Drexhage-like experiment. We study the photoluminescence emitted by the nanorods, focusing on the transitions 5D0 →7F1, 5D0 →7F2 and 5D0 →7F4, as a function of the distance to a gold mirror. We determine the branching electric/magnetic ratios, the oscillators strengths and the quantum yield of these transitions. We finally demonstrate that the nanorods can be used as a vectorial probe of the electric and magnetic contributions to the local density of optical states (LDOS)., Les nanoparticules dopées aux lanthanides constituent une famille polyvalente de nanosondes locales photoluminescentes. Dans ce travail, nous étudions la photoluminescence de nanobâtonnets de NaYF4 dopés à l'Eu3+ caractérisée par un spectre fortement polarisé. Nous développons un modèle théorique complet et une approximation paraxiale de l'émission dipolaire des nanobâtonnets. Nous mesurons la photoluminescence de nanobâtonnets individuels par microscopie confocale de fuorescence et déterminons certaines de leurs propriétés optiques intrinsèques. Nous déterminons également la nature (électrique ou magnétique) et les orientations des moments dipolaires des transitions optiques utiles comme sonde locale dans le domaine visible.En plus du modèle théorique complet et de l'approximation paraxiale, la microscopie de Fourier fournit une troisième méthode pour déterminer l'angle du moment dipolaire, tout en donnant également accès à la hauteur efective des nanobâtonnets. Nous clarfiions également le rôle de la transition électrique et magnétique, y compris les sous-niveaux de Stark dans la formation des images du plan de Fourier, pas pris en compte dans la littérature.En fin, nous utilisons les nanobâtonnets comme sondes pour la densité locale des états optiques en réalisant une expérience de Drexhage. Nous étudions la photoluminescence émise par les nanobâtonnets, en nous concentrant sur les transitions 5D0 →7F1, 5D0 →7F2 et 5D0 →7F4, en fonction de la distance à un miroir en or. Nous déterminons les rapports de branchement électrique/magnétique, les forces des oscillateurs et le rendement quantique de ces transitions. Nous démontrons que les nanobâtonnets peuvent être utilisés comme une sonde vectorielle des contributions électriques et magnétiques à la densité locale d'états optiques (LDOS).

&nbsp

We use the machine learning technique of spars eregression to “reverseengineer” dynamical data to discover the underlying physical model of four wave mixing in nonlinear fibre optics.

International audience

We propose an experimental technique aimed to reveal a fundamental four-wave mixing process resulting in a complete reconstruction of the phase-space topology. The analysis is accompanied by training of a neural network on the experimental data.

We present a novel self-referenced method for the complete temporal characterization (phase and amplitude) of ultrashort optical laser pulses. The technique, called TIme-Gated Electric field Reconstruction (TIGER), measures a second-order nonlinear signal (namely, second harmonic generation or two-photon absorption) produced by four time-delayed replicas of the input pulse. The delays are spatially encoded in the beam profile using a four-faced pyramid-like optical element. The presented technique enables single shot measurement and does not require any spectral measurements, in contrast with well-known self-referenced characterization methods. Depending on the chosen geometry, the recorded TIGER signal can be either interferometric (i.e., carrier frequency resolved) or intensimetric. This paper describes the principle operation of the device together with a detailed theoretical analysis. TIGER measurements of various laser pulse shapes with their reconstructions are then presented demonstrating the relevance of this original approach., Comment: 10 pages, 14 figures

Viscoelastic fluids are currently used for a wide variety of applications in food, chemical, cosmetics and pharmaceutical industries. They are dilute or semi-dilute solutions of high-molecular-weight polymers. For some concentrations, the controlled stretching of the fluid leads to the formation of beads-on-string structures which are characterized by drops connected by a filament. In our case, the controlled extension of the viscoelastic fluid is achieved thanks to an in-house filament stretching device. In order to analyse the 3D dynamic of the beads-on-string structure, i.e. to measure the displacement and the velocity of the bead-like drops during and after the stretching process, we use double exposure Holographic imaging. Holography allows us to choose a 3D volume of space to capture the entire phenomenon. Thanks to Holography, we can focus on one or several planes along the optical axis in order to estimate the 2D coordinates of beads in each plane. The computation of these planes leads to a reconstructed volume where the 3D displacements of beads along the x, y and z axes can be extracted. The dynamic of beads-on-string structures may depend on several factors which are linked to the fluid properties but also to the initial state and elongation parameters. The aim of this work is to experimentally identify the factors which are appropriate to observe a repeatable beads-on-string structure before studying the influence of an orthogonal air current.

International audience; Conformational dynamics of biomolecules, which can span very large time scales ranging from seconds down to femtoseconds, play a key role in their function. In this regard, the combination of the high temporal resolution of ultrafast pump–probe spectroscopy and the structural sensitivity of electronic circular dichroism (CD) spectroscopy provides an extremely promising tool to follow these dynamics with a "virtually" unlimited temporal resolution. However, although CD spectroscopy is a widely used tool in structural biology to determine the secondary structure of biomolecules in solution, transposition of these measurements to the time domain (TRCD), on the sub-picosecond time scale, remains very challenging due to their weak signals prone to pump-induced polarization artifacts. Recent advances in laser technologies and non-linear optics, however, offer new perspectives for the development of femtosecond TRCD set-ups. In this review, we present recent developments in ultrafast TRCD spectroscopy. We discuss the advantages and drawbacks of the few existing functional experimental set-ups for their use to access the conformational dynamics of biomolecules at ultrashort time scales.

International audience

The simulation of lattice Hamiltonians in photonic platforms has been enlightening in the understanding of novel transport and localization properties in the context of solid-state physics. In particular, exciton-polaritons provide a versatile system to investigate these properties in lattices with intriguing band structures in the presence of gain and loss, and particle interactions. Polaritons are hybrid light-matter quasiparticles arising from the strong coupling between photons and excitons in semiconductor microcavities, whose properties can be directly accessed in photoluminescence experiments. In this thesis, we firstly study the features of strained honeycomb lattices made of coupled polariton resonators having high photonic content. In a critically strained lattice, we evidence both a semi-Dirac transport and an anisotropic localization of photons. Secondly, we show that a judicious driving in lattices of lossy resonators allows the appearance of novel localized modes. Using polariton lattices driven resonantly with several optical beams, we demonstrate the localization of light in at-will geometries down to a single site. Finally, we take advantage of the polarization-dependent polariton interaction to demonstrate an optical Zeeman-like effect in a single micropillar. In combination with optical spin-orbit coupling inherent to semiconductor microstructures, the interaction-induced Zeeman effect results in emission of vortex beams with a well-defined chirality. This thesis brings to light the power of polariton platforms to study lattice Hamiltonians with unprecedented properties and it also provides a first step towards the fully-optical generation of topological phases in lattices., La simulation des Hamiltoniens de réseaux dans les plateformes photoniques a permis de mieux comprendre les nouvelles propriétés de transport et de localisation dans le contexte de la physique de l'état solide. En particulier, les exciton-polaritons constituent un système polyvalent permettant d'étudier ces propriétés dans des réseaux avec des structures de bande intrigantes en présence de pertes et de gains, et d'interactions entre particules. Les polaritons sont des quasi-particules hybrides lumière-matière résultant du couplage fort entre les photons et les excitons dans les microcavités semi-conductrices, dont les propriétés peuvent être directement accessibles dans les expériences de photoluminescence. Dans cette thèse, nous étudions premièrement les caractéristiques des réseaux en nid d'abeille déformés, composés de résonateurs de polaritons couplés, à haut contenu photonique. Dans un réseau déformé de façon critique, nous mettons en évidence à la fois un transport semi-Dirac et une localisation anisotrope des photons. Deuxièmement, nous montrons qu'un forçage judicieux dans des réseaux de résonateurs à pertes permet l'apparition de nouveaux modes localisés. En utilisant des réseaux de polaritons sous un forçage résonant par plusieurs faisceaux optiques, nous démontrons la possibilité de localiser la lumière sur différentes géométries, voir jusqu'à un seul site. Enfin, nous profitons de l'interaction de polaritons dépendant de la polarisation pour démontrer un effet optique de type Zeeman dans un seul micropilier. En combinant le couplage spin-orbite optique, inhérent aux microstructures semi-conductrices, avec l'effet Zeeman, induit par l'interaction, nous montrons l'émission de faisceaux de vortex avec une chiralité bien définie. Cette thèse met en lumière la puissance des plateformes de polaritons pour étudier les Hamiltoniens de réseaux avec des propriétés sans précédent. Elle apporte également un premier pas vers la génération, entièrement optique, de phases topologiques dans les réseaux.

We propose to exploit the interaction between surface acoustic waves (SAW) and locally-resonant phononic resonators toachieve coherent driving of micro- nano-mechanical resonators with SAW and, reciprocally, to control SAW propagation at a deep sub-wavelength scale. We investigate the proposed physical system both in the linear and non-linear regimes and reveal the occurrence of Duffing-like nonlinearities and of non-linear coupled mechanical states in the 100-MHz frequency range.&nbsp

Breathing solitons exhibiting periodic oscillatory behaviour form an important part of many different classes of nonlinear wave systems. Recently, thanks to the development of real-time detection techniques, they have also emerged as a ubiquitous mode-locked regime of ultrafast fibre lasers [1,2]. The excitation of breather oscillations in a laser naturally triggers a second characteristic frequency in the system, which therefore shows competition between the cavity repetition frequency and the breathing frequency. The theoretical model describing nonlinear systems with two competing frequencies predicts frequency locking, in which the system locks into a resonant periodic response featuring a rational frequency ratio, and quasi-periodicity following the hierarchy of the Farey tree and the structure of the devil’s staircase [3]. Whilst frequency-locking phenomena have been extensively studied theoretically and experimentally in many physical systems including semiconductor lasers in the field of optics, all the investigations so far relate to systems where an external, accurately controllable modulation adds a new characteristic frequency to the system. Conversely, the link between breathers and frequency locking in fibre lasers is largely missing, arguably because tuning the breathing frequency is a laborious task when done manually, requiring precise control of multiple laser parameters. Here we circumvent this difficulty by a machine-learning approach based on the use of an evolutionary algorithm for the optimisation of the intra-cavity nonlinear transfer function steered by electronically driven polarisation control [4], and we demonstrate that a breather mode-locked fibre laser is a passive system showing frequency locking at Farey fractions [5]. The frequency-locked states, characterised by robustness against parameter (pump power and polarisation) variation and a high signal-to-noise ratio of the breathing frequency, occur in the sequence they appear in the Farey tree and within a pump-power interval given by the width of the corresponding step in the devil’s staircase. The breather laser may therefore serve as a simple model system to explore universal synchronisation dynamics of nonlinear systems. Furthermore, frequency-locked breather lasers can generate wide radiofrequency combs with a line spacing that is not constrained by the length of the laser cavity and can reach the sub-megahertz range, thus representing an attractive alternative to long, unstable fibre cavities for many applications such as in high-resolution spectroscopy. [1] J. Peng, S. Boscolo, Z. Zhao, H. Zeng, Sci. Adv. 5 (2019), eaax1110.[2] J. Peng, Z. Zhao, S. Boscolo, C. Finot, S. Sugavanam, D.V. Churkin, H. Zeng, Laser Photon. Rev. 15 (2021), 2000132.[3] M.H. Jensen, P. Bak, T. Bohr, Phys. Rev. Lett. 50 (1983), 1637.[4] X. Wu, J. Peng, S. Boscolo, Y. Zhang, C. Finot, H. Zeng, Laser Photon. Rev. 1

Chirality is a structural property of molecules lacking mirror symmetry that has strong implications in diverse fields, ranging from life to materials sciences. Established spectroscopic methods that are sensitive to chirality, such as circular dichroism (CD), exhibit weak signal contributions on an achiral background. Helical dichroism (HD), which is based on the orbital angular momentum (OAM) of light, offers a new approach to probe molecular chirality, but it has never been demonstrated on disordered samples. Furthermore, in the optical domain the challenge lies in the need to transfer the OAM of the photon to an electron that is localized on an {\AA}-size orbital. Here, we overcome this challenge using hard X-rays with spiral Fresnel zone, which can induce an OAM. We present the first HD spectra of a disordered powder sample of enantiopure molecular complexes of [Fe(4,4'-diMebpy)3]2+ at the iron K-edge (7.1 keV) with OAM-carrying beams. The HD spectra exhibit the expected inversions of signs switching from a left to a right helical wave front or from an enantiomer to the other. The asymmetry ratios for the HD spectra are within one to five percent for OAM beams with topological charges of one and three. These results open a new window into the studies of molecular chirality and its interaction with the orbital angular momentum of light., Comment: 15 pages, 5 figures

We report the second harmonic scattering experiments from acetonitrile liquid suspensions of two-dimensional metal dichalcogenide nanoflakes,: the semiconducting MoS2 and WS2, the metallic NbS2, and the semi-metallic ZrTe2. Because the study is directly performed in the liquid phase, no symmetry breaking can be attributed to a supporting substrate as it is often the case in the investigation of the second harmonic generation efficiency for these materials. A comparative look of the origin of the nonlinear response using polarization analysis of the hyper Rayleigh scattering intensity is performed. Retardation is clearly exhibited by all nanoflakes considering their average dimensions but remains weak. This is attributed to the non-negligible role played by the nanoflake edges or the presence of surface absorbed polyoxometalates (POMs), in all cases.