Search

International audience; Cargo transport by molecular motors along microtubules is essential for the function of eucaryotic cells, in particular neurons in which axonal transport defects constitute the early pathological features of neurodegenerative diseases. Mainly studied in motor and sensory neurons, axonal transport is still difficult to characterize in neurons of the brain in absence of appropriate in vivo tools. Here, we measured fast axonal transport by tracing the second harmonic generation (SHG) signal of potassium titanyl phosphate (KTP) nanocrystals endocytosed by brain neurons of zebrafish (Zf) larvae. Thanks to the optical translucency of Zf larvae and of the perfect photostability of nanoKTP SHG, we achieved a high scanning speed of 20 frames (of ≈ 90 μ m×60 μ m size) per second in Zf brain. We focused our study on endolysosomal vesicle transport in axons of known polarization, separately analyzing kinesin and dynein motor-driven displacements. To validate our assay, we used either loss-of-function mutations of dynein or kinesin 1 or the dynein inhibitor dynapyrazole, and quantified several transport parameters. We successfully demonstrated that dynapyrazole reduces nanoKTP mobile fraction and retrograde run length consistently, while the retrograde run length increased in kinesin 1 mutants. Taking advantage of nanoKTP SHG directional emission, we also quantified fluctuations of vesicle orientation. Thus, by combining endocytosis of nanocrystals having non-linear response, fast two-photon microscopy, and high-throughput analysis, we are able to finely monitor fast axonal transport in vivo in the brain of a vertebrate, and reveal subtle axonal transport alterations. The high spatiotemporal resolution achieved in our model may be relevant to precisely investigate axonal transport impairment associated to disease models.

Ultrafast laser processing can induce surface nanostructurating (SNS) in most materials with dimensions close to the irradiation laser wavelength. In-situ SNS characterization could be key for laser parameter's fine-tuning, essential for the generation of complex and/or hybrid nanostructures. Laser Induced Periodic Surface Structures (LIPSS) created in the ultraviolet (UV) range generate the most fascinating effects. They are however highly challenging to characterize in a non-destructive manner since their dimensions can be as small as 100 nm. Conventional optical imaging methods are indeed limited by diffraction to a resolution of ≈ 150 nm. Although optical super-resolution techniques can go beyond the diffraction limit, which in theory allows the visualization of LIPSS, most super-resolution methods require the presence of small probes (such as fluorophores) which modifies the sample and is usually incompatible with a direct surface inspection. In this paper, we demonstrate that a modified label-free Confocal Reflectance Microscope (CRM) in a photon reassignment regime (also called re-scan microscopy) can detect sub-diffraction limit LIPSS. SNS generated on a titanium sample irradiated with a λ =257 nm femtosecond UV-laser were characterized with nanostructuring period ranging from 105 nm to 172 nm. Our label-free, non-destructive optical surface inspection was done at 180µm²/s, and the results are compared with commercial SEM showing the metrological efficiency of our approach., L'interaction entre un laser ultrarapide et une objet peut induire une nanostructuration de surface (NSS) dans la plupart des matériaux, avec des dimensions proches de la longueur d'onde du laser d'irradiation. La caractérisation de NSS in-situ pourrait être la clé permettant un réglage fin des paramètres lasers, essentiel pour la génération de nanostructures complexes et/ou hybrides. Les structures de surface périodiques induites par laser (LIPSS) générées par une illumination ultraviolette (UV) génèrent les effets les plus fascinants. Ils sont cependant très difficiles à caractériser de manière non destructive puisque leurs dimensions descendre à 100 nm. Les méthodes d'imagerie optique classiques sont en effet limitées par la diffraction à une résolution de ≈ 150 nm. Bien que les techniques de super-résolution optique puissent aller au-delà de la limite de diffraction, ce qui permet en théorie la visualisation de LIPSS, la plupart des méthodes de super-résolution nécessitent la présence de petites sondes (comme des fluorophores) qui modifient l'échantillon et sont généralement incompatibles avec une imagerie directe des surfaces. Dans cet article, nous démontrons qu'un microscope confocale en réflectance sans marquage (CRM) dans un régime de réallocation de photons (également appelé microscopie de re-scan) peut détecter des LIPSS spis la limite de diffraction. Les NSS générées sur un échantillon de titane irradié avec un laser UV femtoseconde λ = 257 nm ont été caractérisés avec une période de nanostructuration allant de 105 nm à 172 nm. Notre inspection de surface optique sans marquage et non destructive a été effectuée à 180 µm²/s, et les résultats sont comparés avec un MEB commercial montrant l'efficacité métrologique de notre approche.

International audience; Three room-temperature metallomesogens based on Zn(II) cations pentacoordinated by different chelating N^N^N terpyridines and two monodentate gallate co-ligands were designed and synthesized. Depending on the terpyridine ligand's tip functionality, the complexes self-assemble into either a 3D hexagonal mesophase or into a columnar hexagonal mesophase. A systematic study between the structure (molecular architecture, arrangement of the molecules and columns, and chains in both types of mesophases) and photophysical properties (emission maxima and yields, lifetimes of the excited states in the mesophase), correlated with investigations of single molecules in solution, was conducted. Remarkably, one complex exhibited a record quantum yield of 95.0% in solution, while in the mesophase, despite quenching due to the radiative deactivation from the ILCT state, still retained a considerable emission yield of ϕ = 20.2%. The polarized emission of an oriented film, determined for the first time in columnar metallomesogens, shows a dichroic emission ratio (I||/I⊥) of 1.30. DFT and TDDFT computational studies confirmed the origin of the observed fluorescence anisotropy from the transition dipole moment oriented along the C2 symmetry axis of the molecule combined with a high level of order in the 3D mesophase.

Dans le domaine de l’ablation par laser femtoseconde, une classe particulière de faisceaux a récemment attiré une large attention de la part de la communauté scientifique et industrielle : les faisceaux « non-diffractants ». Leur profil transverse varie très peu lorsqu’ils se propagent et ils se révèlent particulièrement efficaces pour déposer de l'énergie à une échelle nanométrique sur de grandes distances à l'intérieur des matériaux transparents. Ceci permet en particulier la découpe de verre et de saphir à des vitesses pouvant atteindre le mètre par seconde. Ces nano-plasmas à très haut rapport de forme posent des défis scientifiques et ouvrent de nouvelles opportunités.

Contrairement au soliton brillant, les solitons à respiration présentent un comportement oscillatoire périodique. L’utilisation des fibres optiques a grandement facilité leur observation: l’interaction sur une grande distance entre la non-linéarité Kerr et la dispersion, en la quasi-absence de dissipation a ainsi permis la caractérisation fine des solitons à respiration d’Akhmediev, de Ma ou bien encore de leur cas limite, le soliton de Peregrine.Grâce au développement des techniques de détection en temps réel, les cavités laser à fibre offrent une autre plateforme extrêmement intéressante. Dans le contexte des lasers ultrarapides à modes bloqués, la génération d’impulsions à respiration constitue un mode de fonctionnement alternatif [1,2] au cas bien répandu où une impulsion aux propriétés toujours identiques est émise à chaque tour de cavité. L’excitation des solutions à respiration déclenche donc spontanément l’émergence d’une seconde fréquence caractéristique dans le système. Cette deuxième fréquence sera plus faible que la fréquence associée à la cavité, i.e. la fréquence de répétition. Or les systèmes non linéaires à deux fréquences concurrentes peuvent conduire à un verrouillage de fréquence, conduisant à une réponse périodique résonante avec un rapport de fréquence rationnel [3].Bien que les phénomènes de verrouillage de fréquence aient fait l’objet d’études théoriques et expérimentales approfondies dans de nombreux systèmes physiques, y compris les lasers à semi-conducteurs dans le domaine de l’optique, les recherches menées jusqu’à présent concernent essentiellement des systèmes dans lesquels une modulation externe, contrôlable avec précision, ajoute une nouvelle fréquence caractéristique au système. Le cas d’une seconde fréquence émergeant naturellement a par contre été très peu discuté. Cela s’explique en grande partie par la difficulté expérimentale d’atteindre de manière précise ces régimes à respiration. Pour simplifier cette tache laborieuse, nous avons mis en place une approche d’apprentissage automatique basée sur l’utilisation d’un algorithme évolutionnaire pour l’optimisation de la fonction de transfert non linéaire intra-cavité [4]. Nous démontrons alors qu’un laser à fibre verrouillé par un mode de respiration est un système montrant un verrouillage de fréquence [5]. Ces états sont caractérisés par une robustesse à la variation des paramètres (puissance de pompage et polarisation) et un rapport signal/bruit nettement amélioré. Ils se produisent dans l’ordre où ils apparaissent dans l’arbre de Farey et dans un intervalle de puissance de pompagedonné par la largeur de la marche correspondante dans l’escalier du diable.[1] J. Peng, S. Boscolo, Z. Zhao, H. Zeng, Sci. Adv. 5 (2019), eaax1110.[2] J. Peng et al., Laser Photon. Rev. 15 (2021), 2000132.[3] M.H. Jensen, P. Bak, T. Bohr, Phys. Rev. Lett . 50 (1983), 1637.[4] X. Wu et al., Laser Photon. Rev. 16 (2), 2100191[5] X. Wu et al., Nat. Commun. 13 (1), 5784

L’équation de Schrödinger non linéaire régit l’évolution des ondes dans de nombreux domaines non linéaires tels que l’hydrodynamique, la physique des plasmas, les condensats de Bose-Einstein et l’optique fibrée. Dans ce dernier cas, l’onde subit des changements dans un milieu dispersif combiné à un déphasage non linéaire dépendant de l’intensité. Le processus clé sous-jacent est le mélange à quatre ondes, qui décrit l’échange d’énergie entre des composantes de fréquence discrètes. En raison de la croissance des bandes latérales additionnelles et des pertes optiques qui limitent la distance d’interaction potentielle, il est notoirement difficile d’observer expérimentalement la dynamique idéale de mélange à quatre ondes. Afin de résoudre ce problème, nous proposons de modifier itérativement les conditions de phase et d’amplitude d’un signal composé de trois raies spectrales également espacées qui est ensuite injecté dans un court segment de fibre optique [1]. Une telle approche segmentée nous permet d’imiter une propagation idéalisée sur des dizaines de kilomètres - une distance qui dépasse largement la fibre de 500 m utilisée. Notre étude expérimentale révèle la topologie complète de l’espace de phase présentant plusieurs cycles de récurrence de Fermi-Pasta-Ulam-Tsingou, l’existence d’une onde stationnaire ainsi que la présence d’une séparatrice qui marque la transition entre deux régimes d’évolution spatio-temporelle distincts [2]. Lorsqu’elle est tracée sur un portrait de phase, la dynamique des ondes suit des orbites proches qui sont définies de manière unique par les conditions initiales, et qui ne se croisent pas. En changeant brusquement au cours de la propagation les paramètres de contrôle, tels que la puissance moyenne, nous démontrons à la fois théoriquement et expérimentalement qu’il est possible de connecter deux états qui ne sont pas initialement situés sur la même trajectoire fermée [3]. Enfin, nous étudions également les avantages des techniques d’apprentissage automatique supervisées de deux manières différentes. Tout d’abord, nous combinons des mesures non itérées avec un réseau neuronal [4]. Les résultats démontrent que le réseau peut extraire les caractéristiques clés de la topologie de l’espace des phases et peut prévoir avec précision la dynamique non linéaire. Deuxièmement, nous avons mis en œuvre les techniques d’identification clairsemée de la dynamique non linéaire. À partir d’un ensemble de plusieurs trajectoires pouvant être potentiellement affectées par le bruit, nous sommes en mesure de récupérer quantitativement les termes directeurs dans les systèmes d’équations différentielles [5].[1]A. Sheveleva et al., Optica 9, 656-662, 2022.[2]G. Cappellini and S. Trillo, J. Opt. Soc. Am. B 8, 824-838, 1991.[3]A. Sheveleva et al. Optics Communications, in press, 2023, arXiv:2303.08469.[4]A. Sheveleva et al., Opt. Lett. 47, 6317-6320, 2022.[5]A. V. Ermolaev et al., Sci Rep, 12, 12711, 2022.

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.

International audience; Individual nanoparticle spectroscopic characterization is fundamental, but challenging in liquids. While confocal selectivity is necessary to isolate a particle in a crowd, Brownian motion constantly offsets the particle from the light collection volume. Here, we present a system able to acquire holograms and reconstruct them to precisely determine the 3D position of a particle in real time. These coordinates drive an adaptive system comprising two galvanometric mirrors (x,y, transverse directions) and a tunable lens (z, longitudinal) which redirect light scattered from the corresponding region of space towards the confocal entrance of a spectrometer, thus allowing long spectral investigations on individual, freelymoving particles. A study of the movements and spectra of individual 100 nm Au nanoparticles undergoing two types of aggregations illustrates the possibilities of the method.

Electrochemistry exploits local current heterogeneities at various scales ranging from the micrometer to the nanometer. The last decade has witnessed unprecedented progress in the development of a wide range of electroanalytical techniques allowing to reveal and quantify such heterogeneity through multiscale and multifonctionnal operando probing of electrochemical processes. However most of these advanced electrochemical imaging techniques, employing scanning probes, suffer from either low imaging throughput or limited imaging size. In parallel, optical microscopies, which can image a wide field of view in a single snapshot, have made considerable progress in terms of sensitivity, resolution and implementation of detection modes. Optical microscopies are then mature enough to propose, with basic bench equipment, to probe in a non destructive way a wide range of optical (and therefore structural) properties of a material in situ, in real time: under operating conditions. They offer promising alternative strategies for quantitative high-resolution imaging of electrochemistry. The first sections recall the optical properties of materials and how they can be probed optically. They discuss fluorescence, Raman, surface plasmon resonance, scattering or refractive index. Then the different optical microscopes used to image electrochemical processes are examined along with some strategies to extract quantitative electrochemical information from optical images. Finally the last section reviews some examples of in situ imaging, at micro- to nanometer resolution, and quantification of electrochemical processes ranging from solution diffusion to the conversion of molecular interfaces or solids., Comment: 66 pages, 23 figures. To be published in Encyclopedia of Electrochemistry

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).

Oral; International audience

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

Numerous techniques for the fabrication of microlenses in optical fiber tips exist. My numerical studies to focus the light below the diffraction limit in the fiber tip and to form beams qualified as photonic jets, led me to consider microlenses with strong curvatures which rest only on the core. However, such lenses were very difficult to produce, especially for single-mode fibres. The fibre end caps that had been produced in the literature up to that point were mainly produced by thermoforming. Lensing by fusion is well suited for multimode fibres, but less so for single-mode fibres where the core is almost 10 times smaller than the cladding. We have therefore proposed a new method of manufacturing a microlens for optical fibres, which has been patented. I also set up a set-up that allowed us to experimentally characterise the focal volume of photonic jets obtained by direct imaging. This allowed to validate the quality of the manufactured microlenses., De nombreuses techniques de fabrication de microlentilles en embout de fibre optique existent. Mes études numériques pour focaliser la lumière en deçà de la limite de diffraction en embout de fibre et former des faisceaux qualifiés de jets photoniques, m’ont amené à considérer des microlentilles à fortes courbures qui s’appuient uniquement sur le cœur. De telles lentilles étaient cependant très difficiles à réaliser, qui plus est pour les fibres monomodes. Les embouts de fibre réalisés jusque-là dans la littérature l’avaient été principalement par thermoformage. La réalisation de lentille par fusion convient bien pour les fibres multimodes mais moins pour les monomodes pour lesquelles le cœur a une dimension près de 10 fois plus petite que la gaine. Nous avons donc proposé une nouvelle méthode de fabrication de microlentille pour fibre optique, qui a été brevetée. J’ai également mis en place un montage qui a permis caractériser expérimentalement le volume focale des jets photoniques obtenus par imagerie directe. Ce qui a permis de valider la qualité des microlentilles fabriquées.

International audience; Internet of things (IoT) technology is based on connecting each real object to the internet. Every single object is uniquely recognized and reachable over the network. IoT last mile connectivity is based on different communication technologies and protocols, where the majority is categorized as short-range networks that operate in ISM bands like Zigbee, Wi-Fi, and Bluetooth. Short-range technologies were successfully tested and deployed in different industrial sectors. However, in the energy sectors, the deployment is challenging in certain hard to reach areas where reliable last-mile connectivity is required between the home area network (HAN) smart meters and the meter data management system (MDMS). Therefore recently, Low Power Wide Area Network (LPWAN) technology implementations, which offer long-range connectivity, has emerged as a promising alternative for IoT in Energy applications. Within LPWAN, a variety of technology implementations exist and operate in licensed and unlicensed spectrum respectively like NB-IoT, LoRaWAN, and Sigfox. In this article, we discuss both the performance of LoRaWAN in a real-world environment and its deployment as a low-cost, long-range, and reliable last-mile solution for energy smart metering in urban area scenario where a short-range solution may not be the optimum one. Furthermore, a prototype that is adapted to the existing Lebanese traditional energy sector was developed to test LoRaWAN's usefulness in Lebanon.

We propose FluoGAN, an unsupervised hybrid approach combining the physical modelling of fluorescence microscopy timelapse acquisitions with a generative adversarial learning procedure for the problem of image deconvolution. Differently from standard approaches combining a least-square data term based on one (long-time exposure) image with sparsity-promoting regularisation terms, FluoGAN relies on a data term being the distributional distance between the fluctuating observed timelapse (short-time exposure images) and the generative model. Such distance is computed by adversarial training of two competing architectures: a physics-inspired generator simulating the fluctuating behaviour as a Poisson process of the observed images combined with blur and undersampling, and a standard convolutional discriminator network. FluoGAN is a fully unsupervised approach requiring only a fluctuating sequence of blurred, undersampled and noisy images of the sample of interest as input. It can be complemented with prior knowledge on the desired solution such as sparsity, non-negativity etc. After having described the main ideas behind FluoGAN, we formulate the corresponding optimisation problem and report several results on simulated and real phantoms used by microscopy engineers to quantitatively assess spatial resolution. The comparison of FluoGAN with state-of-the-art methodologies shows improved resolution, allowing for high-precision reconstructions of fine structures in challenging real Ostreopsis cf Ovata data. The FluoGAN code is available at: https://github.com/cmayeul/FluoGAN.

International audience; Protoporphyrin IX (PpIX) is a fluorophore now used to identify tumoral tissues. The tissue is usually excited at one wavelength, e.g., 405 nm, and the fluorescence signal generated by this molecule and other fluorophores (the baseline) is used to estimate the amount of PpIX. However, fluorophores too close to PpIX impair the estimation and resulting classifications. Thus, we handle this issue by suggesting an efficient multi-excitation wavelengths method, free from any a priori on the baseline. Our method aims to distinguish healthy tissues from tumor margins, while being more robust to baseline variability. It keeps an ability to distinguish healthy from tumor tissues up to 87% in cases where existing methods'ability drops near 0%.

Microstructured optical fibres (MOFs), also known as Photonic Crystal Fibres (PCFs) or Holey Fibres (HFs), play an important role in supercontinuum generation because of their high nonlinearity and ability to tailor the dispersion profile. Nowadays, studies have extended to the multimode environment to enhance spectral broadening by taking advantage of various intermodal nonlinear effects. Recently, it has been shown that these types of fibres can also be able to provide spatially cleaned output beams through a novel nonlinear spatial effect called Kerr-induced beam self-cleaning (KBSC), which makes these fibres suitable for a variety of multimode-based applications. In this paper, a full modal analysis of germanium (Ge)-doped graded-index multimode PCFs with different geometrical sizes is provided. The influence of fibre size on modal properties, such as effective refractive index, birefringence and dispersion, was investigated using the finite element method. It was found that the changes in the geometric parameters can significantly affect the modal properties and then the frequency generation and spectral broadening. Experimentally, high-efficiency frequency generation with different frequency detunings was obtained in a short length of each PCF by launching input pulses at 1064 nm pump wavelength. For longer fibre length and high input power, supercontinuum generation with improved broadening from visible to near IR by intermodal four-wave mixing and stimulated Raman scattering was observed in all PCFs. A study of the effect of input peak power, input polarization axis and fibre length on supercontinuum spectrum is presented. Experimental evidence of the KBSC effect as a function of various fibre and laser parameters is also reported. The evolution of spatial output beam pattern from higher-order mode to fundamental mode with low-peak-power self-cleaning threshold was observed for all the fibres by launching a 1064 nm pump laser with 1 ns pulse duration.

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.

International audience; Optogenetic techniques have been developed to allow control over the activity of selected cells within a highly heterogeneous tissue, using a combination of genetic engineering and light. Optogenetics employs natural and engineered photoreceptors, mostly of microbial origin, to be genetically introduced into the cells of interest. As a result, cells that are naturally light-insensitive can be made photosensitive and addressable by illumination and precisely controllable in time and space. The selectivity of expression and subcellular targeting in the host is enabled by applying control elements such as promoters, enhancers and specific targeting sequences to the employed photoreceptor-encoding DNA. This powerful approach allows precise characterization and manipulation of cellular functions and has motivated the development of advanced optical methods for patterned photostimulation. Optogenetics has revolutionized neuroscience during the past 15 years and is primed to have a similar impact in other fields, including cardiology, cell biology and plant sciences. In this Primer, we describe the principles of optogenetics, review the most commonly used optogenetic tools, illumination approaches and scientific applications and discuss the possibilities and limitations associated with optogenetic manipulations across a wide variety of optical techniques, cells, circuits and organisms.

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.

Passive mode-locked lasers are valued by scientists and industry for their ability to generate ultra-short (femtosecond) pulses. In ultra-high intensity facilities, these lasers are used to produce an energetic (nanojoule) and femtosecond pulse that will be amplified by a chirped pulse amplification method in order to reach the necessary energy (kilo joule) to obtain a considerable post-compression/focusing intensity, in the range of 10^20 W/cm2 such as PETAL facility. Developed in the 80's, the passive mode-locking technology by spatial Kerr effect (Ti:Sa oscillator) allows to obtain the best performances in terms of low pulse duration / energy couple. However, their free space architecture causes integration problems and requires regular maintenance. There is another technology based on a passive mode-locking by temporal Kerr effect called Mamyshev oscillator. Recent developments have shown the ability of these new oscillators to compete with Ti:Sa oscillators while adopting an all-fiber architecture. Fiber sources are greatly appreciated by laser users due to their compactness and robustness. The objective of this thesis is therefore to design and develop a compact and robust Mamyshev oscillator in agreement with the needs of the PETAL facility. After having reviewed the Mamyshev oscillators state of art, we will present our single-mode fully-fiber polarization-maintaining oscillator emitting around 1μm, able of operating at several repetition rates (from 7.7 to 107.8MHz) due to the harmonic regime phenomenon. This allows our oscillator to deliver a significant average power up to 1.3W. We will present a numerical/experimental study on the origin of these harmonic regimes, which was previously little understood and subject to debate. We will also expose stability studies that we have performed in order to obtain a stable mode of operation in the fundamental regime able to reach 48nJ per pulse for a post-compression duration up to a few tens femtoseconds. Finally, we will put forward the first characterization of the intensity and phase noise of a fully-fiber Mamyshev oscillator., Les lasers à blocage de modes passifs sont appréciés par les scientifiques et les industriels pour leur capacité à générer des impulsions ultra-courtes (femtoseconde). Au sein des installations ultra-haute intensité, ces lasers sont utilisés pour produire une impulsion énergétique (nanojoule) et femtoseconde qui sera amplifiée par la suite dans un dispositif d'amplification à dérive de fréquence afin d'atteindre l'énergie nécessaire (kilo joule) pour obtenir post-compression / focalisation une intensité considérable, de l'ordre de 10^20 W/cm2 pour une installation telle que PETAL. Développée dans les années 80, la technologie du blocage de modes passif par effet Kerr spatial (oscillateur Ti :Sa) permet d'obtenir les meilleures performances en terme de couple faible durée d'impulsion / énergie. Néanmoins, leur architecture en espace libre pose des problèmes d'intégration et implique une maintenance régulière. Il existe une autre technologie basée sur un blocage de modes passif par effet Kerr temporel appelée oscillateur Mamyshev. Des développements récents ont montré la capacité de ces nouveaux oscillateurs à rivaliser avec les oscillateurs Ti :Sa tout en adoptant une architecture entièrement fibrée. Les sources fibrées sont grandement appréciées par les utilisateurs en raison de leur compacité et de leur robustesse. L'objectif de cette thèse est donc de concevoir et de développer un oscillateur Mamyshev compact et robuste compatible avec les besoins de l'installation PETAL. Après avoir dressé un état de l'art des oscillateurs Mamyshev présents dans la littérature, nous présenterons notre oscillateur monomode à maintien de polarisation entièrement fibré émettant aux alentours de 1μm, capable de fonctionner à plusieurs cadences (de 7,7 à 107,8MHz) en raison du phénomène de régime harmonique. Ceci permet à notre oscillateur de délivrer une puissance moyenne importante allant jusqu'à 1.3W. Nous exposerons une étude numérique / expérimentale sur l'origine de ces régimes harmoniques jusqu'alors peu comprise et sujette à débat. Nous présenterons également des études de stabilité que nous avons réalisées afin d'obtenir un mode de fonctionnement stable en régime fondamental capable de délivrer des impulsions de 48nJ pour une durée post compression pouvant aller jusqu'à quelques dizaines de femtosecondes. Enfin, nous mettrons en avant la première caractérisation du bruit d'intensité et de phase d'un oscillateur Mamyshev entièrement fibré.

Nonlinear optics has been a productive field of research and investigation for a few decades now, but the rapid progression of photonic integration platforms in recent years has opened up a whole new range of applications. On-chip integration of effective saturable absorbers and secondary sources including Brillouin laser, supercontinua, or frequency combs are few examples of the very wide possibilities offered by nonlinear nanophotonics. In this context, materials with large third-order optical nonlinearities become highly sought after, as they enable the development of nonlinear functionalities at low input powers. Given a large number of potential candidates as material for nonlinear nanophotonics, it becomes even more important to be able to measure their nonlinear optical response.The two most common techniques for measuring the optical nonlinearity of materials are the Z-scan and four wave mixing (FWM) techniques. The Z-scan method can only be applied to bulk materials, and not to optical waveguides such as the ones used in nanophotonics. In contrast, FWM can measure nonlinearities in waveguides but requires a phase matching, waveguides with low losses and high optical power.This thesis report an interferometric technique relied on heterodyne detection to measure the Kerr index of nonlinear materials. The different stages of the technique implementation have been presented as well as the data processing method. We applied this technique to nonlinear materials of different compositions such as silicon nitride, chalcogenides and silicon-on-insulator. The heterodyne interferometer is not only suitable for integrated waveguides but also for fibers and microfibers. This method has the advantage of being highly sensitive, and is therefore well-adapted to short waveguides or lossy materials. Such a tool would be useful to control nonlinearity and of great help in the development of new materials for integrated photonics., La progression rapide de la photonique intégrée ces dernières années a ouvert un large éventail d’applications. L’intégration sur puce des absorbants saturables ou des sources secondaires comme le laser Brillouin, le supercontinuum ou les peignes de fréquence sont quelques exemples. Dans ce contexte, les matériaux présentant une grande non-linéarité optique du troisième ordre sont de plus en plus recherchés, comme le silicium ou les verres de chalcogénure. En effet, ils permettent le développement des fonctionnalités non-linéaires à une basse puissance injectée. Compte tenu du grand potentiel de ces matériaux pour la nanophotonique non-linéaire, il s’avère encore plus important de développer des méthodes de mesure pour déterminer la réponse optique non-linéaire de ces matériaux.À ce jour, parmi les techniques les plus courantes pour mesurer la non-linéarité, on retient la méthode Z-scan, qui est utilisée uniquement pour des matériaux bruts, et la méthode du mélange à quatre ondes (FWM) qui est compatible avec les guides d’ondes, mais requiert un accord de phase et des guides avec très peu de pertes, ce qui nécessite de disposer d’une filière technologique de nanofabrication déjà mature.Nous rapportons dans cette thèse, une méthode interférométrique basée sur la détection hétérodyne pour la mesure de l’indice Kerr des matériaux non-linéaires. Les différentes étapes de la mise en place de la technique et le procédé de traitement de données ont été détaillés dans ce manuscrit. La méthode a été appliquée à des matériaux non-linéaires de différentes compositions comme le nitrure de silicium, les chalcogénures et le silicium-sur-isolant, où certains d’entre eux présentent de l’absorption à deux photons que nous avons mesurée avec cette même technique. L’interféromètre hétérodyne est adapté à des guides d’ondes intégrés, mais aussi à d’autres structures guidantes telles que des fibres macroscopiques ou des microfibres. Cette technique extrêmement sensible permet de mesurer des petits déphasages non-linéaires à des puissances modérées et pour des guides présentant des grandes pertes de propagation. Un tel outil serait utile pour contrôler la non-linéarité et pour participer au développement de nouveaux matériaux pour la photonique intégrée.

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.