HAL Portal IOGS (nstitut d'Optique Graduate School)
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Continuous wave tunable laser from 616 nm to 637 nm based on a compact sum frequency generation setup
No full textInternational audienceWe report on a compact sum frequency generation (SFG) setup generating continuously tunable single-frequency visible radiation from 616 nm to 637 nm, starting from two tunable laser sources at 1 µm and 1.5 µm. We compare two types of crystals: periodically poled lithium niobate (PPLN) and periodically poled magnesium oxide-doped lithium niobate (PPMgOLN), both custom-made such that the tunability range is achieved via temperature control only. We achieve a Watt level of power over the entire tunability range in PPMgOLN, with a mode profile enabling 80% coupling efficiency in a single-mode fiber, limited by the IR sources' tunability, while keeping the system easy to operate
Theia and HWO astrometric power for Giant Exoplanets around solar-type stars
No full textInternational audienceTheia and HWO are respectively ESA astrometry mission and NASA astrometry instrument designed to achieve a precision of 0.3 μas, enabling ultra-precise measurements of stellar positions. When focused on giant planet detection, Theia and HWO astrometry mode can carry out a large-scale census of Jupiter-like planets orbiting stars at 150 parsecs and beyond, including systems that are inaccessible to radial velocity due to high stellar activity or youth. This provides a valuable insight into the early dynamical evolution of planetary systems and offers important constraints on the formation and migration mechanisms of giant planets. Theia’s and HWO astrometry complements radial velocity (RV) measurements by providing true planetary masses and full orbital inclinations. It can also reveal mutual inclinations in multi-planet systems, helping to map the three-dimensional architecture of planetary systems. Furthermore, its 0.33 deg2 field enables the astrometric monitoring of stars up to ten magnitudes fainter than the primary targets, greatly increasing its statistical reach. Theia and HWO astrometry mode can also identify prime targets for direct imaging and atmospheric characterization for future missions
Contextual Hypernetwork for Adaptive Prediction of Laser-Induced Colors on Quasi-Random Plasmonic Metasurfaces
No full textInternational audienceLaser processing is a rapid, versatile, and low-cost technology to print images on large surfaces. When applied to very thin films embedded with disordered metallic nanoparticles, known as quasi-random plasmonic metasurfaces, it generates colors that vary with the observation mode, making it valuable for visual security applications. Predicting these colors in different modes from the knowledge of laser processing parameters and the initial state of the metasurface can accelerate the industrialization process. However, there is no general physical model able to make this prediction accurately in various modes. In order to address this issue, this paper proposes a data-driven approach for learning deep models on experimental data able to predict the colors observed in different environments for a large range of laser processing parameters. We leverage a framework that learns jointly a shared latent space for multiple environments together with a contextual representation specific to each. This contextual representation is generated by an hypernetwork conditioned on an interpretable context vector. This context vector can be learned from few data allowing fast adaptation to new environments. This approach demonstrates that a single model can learn to predict a large range of colors across different environments. Its effectiveness is demonstrated through its ability to rapidly adapt to new scenarios with minimal data and to serve as an improved weight initializer for finetuning when larger datasets are available. Source code and datasets are available on Gitlab
Cr:ZnSe as a luminescent concentrator
No full textInternational audienceWe demonstrate the first Cr:ZnSe luminescent concentrator. Enhanced by amplified spontaneous emission, it has the best efficiency ever reported for luminescent concentrators emitting in the SWIR band. It emits an output power of 1.6 W and a brightness of 5.4 W/cm 2 /sr over a broadband spectrum between 2.1 µm and 2.6 µm. It has a remarkably simple setup using a fibre-coupled laser diode at 1530 nm as a pump source
Protection des System-on-Chips par l'isolation : Le paysages des TEE dans le monde de l'embarqué
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Saturating interaction in coherently coupled two-component Bose-Einstein condensates
No full textRabi-coupled spinor Bose-Einstein condensates, with competing intra-and interspecies interactions, enable independent control of two-and three-body interactions. We show that coupling can also drive the system into a strongly nonlinear regime of saturating interaction. More precisely, the equation of state interpolates between low-and high-density regimes described by two different two-body scattering lengths. Interestingly, the transition can be determined by the strength of the coupling. We experimentally demonstrate this saturation phenomenon by measurements of the interaction energy of a Bose-Einstein condensate as a function of the detuning and of the strength of the Rabi coupling in spin mixtures of potassium 39
Particle tracking with continuous energy minimization for the study of segregation in bedload transport
No full textInternational audienceBedload transport, the coarser component of sediment transport moving in contact with the bed in stream channels, has major implications for public safety, water resources, and environmental sustainability. Size segregation is largely responsible for our limited ability to predict sediment flux and river morphology, particularly in mountains where steep slopes drive an intense transport of a wide range of grain sizes. Two-size experiments were carried out in a dedicated 10% steep flume to study vertical segregation at the grain scale. Particle tracking was used to obtain trajectories of high concentration bedload mixtures of spherical particles but it fails to correctly retrieve long trajectories due to strong grain-grain interactions. In this paper we propose a new particle tracking algorithm using a global optimization scheme based on a Continuous Energy function and a specific iterative Minimization (CEM). For the purpose of evaluating this new algorithm named CEM-ST * , we have designed two * available at https://gitlab.univ-st-etienne.fr/labhc-iscv/cem-st</div
Dynamic Ultrafast Laser-Induced Structural Changes and Extreme Nanostructuring in Hard Dielectric Materials
No full textInternational audienceUnderstanding matter transformation under light enables ultrafast 3D laser structuring to attain precise control down to the nanoscale. This is challenging for hard crystals given their mechanical resistance; nonetheless, it is key in structurally designing matter, pendling between crystalline and amorphous phases. The particular time evolution of structural and morphological changes can pinpoint either dynamics related to shock compaction or to thermal relaxation with phase transition. We report quantified the time-resolved dynamics of laser modifications induced by nondiffractive ultrafast laser beams in bulk sapphire using qualitative and quantitative phase-contrast microscopy to link optical changes to thermodynamic and structural evolutions. The final morphological changes of irradiated structures are revealed by high-resolution electron microscopy. Observations confirm that Bessel pulse irradiation transforms the pristine crystalline structure into a homogeneous amorphous phase in tens of ns, via the passage through a liquid phase nucleated at the early stages of the process. This ns-lived liquid phase is subject to cavitation at higher energy concentrations on the cooling phase (100 ns), facilitating nanoscale void fabrication with high aspect ratios. The outcomes strongly support bulk modification without shock assistance, governed instead by thermal relaxation. This determines a robust path for extreme laser structuring down to the nanoscale
Collective States of α-Sexithiophene Chains Inside Boron Nitride Nanotubes
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Entanglement of quasiparticles in a modulated Bose-Einstein condensate
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