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Chaotic dynamics in passively Q-switched Tm:LiYF4 laser operating at 2.3 μ m on the 3H4 → 3H5 transition
No full textInternational audienceWe report on the chaotic dynamics in a passively Q-switched 2.3-μm thulium laser operating on the 3H4 → 3H5 transition. The experiment exploits a Tm:LiYF4 crystal and various laser cavity configurations, involving an optional cascade laser on the 3F4 → 3H6 transition at 1.9 μm. The saturable absorber employed is Cr2+:ZnSe, which is exclusively saturated by the 2.3 μm laser. An analysis of the Q-switched dynamics shows a pronounced inclination of the laser operation toward the unstable and chaotic behavior. To understand the origins of this chaos, we monitor the population of the metastable 3F4 level via cascade laser operation at 1.9 μm, underlying this variable as an interesting parameter to survey chaotic instabilities
Étude des interactions des lasers courts et ultra-courts avec les métaux et les semi-conducteurs à travers des simulations atomistiques détaillées.
No full textInternational audienceShort and ultrashort laser pulses are widely utilized for material ablation, micro- and nanostructuring, as well as for the creation of periodic surface and volume structures such as ripples and volume nanogratings [1-2]. The interaction of these lasers with materials induces a range of non-equilibrium effects that lead to structural transformations, damage, and/or ablation, depending on the experimental conditions. In this study, we employ atomistic simulations (two-temperature model and molecular dynamics, TTM-MD) to investigate material modifications under these conditions [3].For metallic targets, we demonstrate that at very low laser fluences, melting and solidification processes result in defect formation, which alters properties such as surface wettability. Additionally, phenomena such as surface cooling, oxidation, and structural formation play significant roles. As the laser fluence increases, material ablation results in the ejection of a mixture of gas and nanoparticles. In the case of semiconductors like silicon, low-fluence regimes lead to melting and amorphization (Figure 1), which are influenced by crystal orientation and cooling rates. Furthermore, periodic structures form on the surface in this regime with laser irradiation-dependent parameters. At higher fluences, phase explosion causes ejection of nanoparticles from the target. We also examine laser interactions with nanoparticles, providing guidelines for selecting appropriate laser parameters for their fragmentation. Lastly, we discuss the possible anisotropy of these interactions appearing in the case of nanoaggregates.[1] T.J.Y. Derrien, T.E. Itina, R Torres, T. Sarnet, M. Sentis, J. App. Phys, 2013 114(8), 083104. [2] A. Rudenko, H. Ma, V. P. Veiko, J. P. Colombier, T. E. Itina, Appl. Phys. A, 2018, 124, 1-11.[1] M. E. Povarnitsyn, V. B. Fokin, P.R. Levashov, T. E. Itina, Phys. Rev. B, 2015 92(17), 174104.Les impulsions laser courtes et ultra-courtes sont largement utilisées pour l'ablation des matériaux, la micro- et nanostructuration, ainsi que pour la création de structures périodiques en surface et en volume, telles que des ondulations et des nanoréseaux volumétriques [1-2]. L'interaction de ces lasers avec les matériaux induit une gamme d'effets hors équilibre qui entraînent des transformations structurelles, des dommages et/ou une ablation, selon les conditions expérimentales. Dans cette étude, nous utilisons des simulations atomistiques (modèle à deux températures et dynamique moléculaire, TTM-MD) pour étudier les modifications des matériaux dans ces conditions [3].Pour les cibles métalliques, nous démontrons qu'à de très faibles fluences laser, les processus de fusion et de solidification provoquent la formation de défauts, modifiant des propriétés telles que la mouillabilité de la surface. De plus, des phénomènes tels que le refroidissement de la surface, l'oxydation et la formation de structures jouent des rôles importants. À mesure que la fluence du laser augmente, l'ablation du matériau entraîne l'éjection d'un mélange de gaz et de nanoparticules. Dans le cas des semi-conducteurs comme le silicium, les régimes de faible fluence conduisent à la fusion et à l'amorphisation (Figure 1), qui sont influencées par l'orientation cristalline et les vitesses de refroidissement. En outre, des structures périodiques se forment en surface dans ce régime, avec des paramètres dépendant de l'irradiation laser. À des fluences plus élevées, l'explosion de phase provoque l'éjection de nanoparticules depuis la cible. Nous examinons également les interactions laser avec les nanoparticules, en fournissant des lignes directrices pour choisir les paramètres laser appropriés pour leur fragmentation. Enfin, nous discutons de l'anisotropie possible de ces interactions apparaissant dans le cas des nanoagrégats.[1] T.J.Y. Derrien, T.E. Itina, R. Torres, T. Sarnet, M. Sentis, J. App. Phys, 2013 114(8), 083104. [2] A. Rudenko, H. Ma, V. P. Veiko, J. P. Colombier, T. E. Itina, Appl. Phys. A, 2018, 124, 1-11. [3] M. E. Povarnitsyn, V. B. Fokin, P.R. Levashov, T. E. Itina, Phys. Rev. B, 2015 92(17), 174104
Comparative Study on the Interest in Non-Uniform Rational B-Splines Representation versus Polynomial Surface Description in a Freeform Three-Mirror Anastigmat
No full textInternational audienceNovel freeform optical design methods can be classified in two categories, depending on whether they focus on the generation of a starting point or the development of new optimization tools. In this paper, we design a freeform three-mirror anastigmat (TMA) and compare different surface representations using either a differential ray tracer as a new optimization tool or a commercial ray tracer (ANSYS-ZEMAX OpticStudio). For differential ray tracing, we used FORMIDABLE (Freeform Optics Raytracer with Manufacturable Imaging Design cApaBiLitiEs), an optical design library with differential ray tracing and Non-Uniform Rational B-Splines (NURBS) optimization capabilities, available under the European Software Community License (ESCL). NURBS allow a freeform surface to be represented without needing any prior knowledge of the surface, such as the polynomial degree in polynomial descriptions. OpticStudio and other commercial optical design software are designed to optimize polynomial surfaces but are not well-suited to optimize NURBS surfaces, requiring a custom optical design library. In order to demonstrate the interest in using NURBS representation, we designed and independently optimized two freeform telescopes over different iteration cycles; with NURBS using FORMIDABLE or with XY polynomials using OpticStudio. We then compared the resulting systems using their root mean square field maps to assess the optimization quality of each surface representation. We also provided a full-system comparison, including mirror freeform departures. This study shows that NURBS can be a relevant alternative to XY polynomials for the freeform optimization of reflective three-mirror telescopes as it achieves more a uniform imaging quality in the field of view
Dose rate effects in Ag-doped metaphosphate glass RPL dosimeters up to MGy range
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Investigation of the Radiation Response of a Dual-Stage Optical Amplifier
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Exploring the architectures of nearby exoplanetary systems using high-precision space astrometry
No full textInternational audienceTo increase the accuracy of measurements obtained by global astrometry on specific astronomical objects, it is necessary to devote more observation time to determining their relative position with respect to the stars in the field of view. In ESA latest prospective study, the Senior Committee recognized that, after Gaia, "the next steps in space astrometry could be to improve by one order of magnitude relative astrometric accuracy ". The Theia mission was submitted in 2022 to ESA, using a diffraction-limited telescope about 1m in diameter and with a field of view of 0.5 degrees, capable of achieving sub-microsecond angular accuracy. Such precision makes it possible to study the architecture of exoplanetary systems close to the Sun, down to the mass of the Earth. We will present this space mission project, its detection capabilities and how this M-class project could be beneficial for understanding the architectures of nearby exoplanetary systems
LiRoT
No full textThe Semantic Web of Things enhances the Internet of Things with Web technologies as well as Knowledge Graphs and reasoning. Traditional reasoners are too heavy in terms of memory footprint and/or processing time to be implementable on things. LiRoT is a lightweight incremental reasoner that can be embedded in constrained objects, so that reasoning on them in a fog architecture becomes possible. The focus of this work is to reduce drastically memory footprint while paying attention to processing time, hence usual optimization techniques are not fully adequate.Le Web Sémantique des Objets intègre des technologies du Web à l'Internet des Objets, ainsi que des graphes de connaissances et du raisonnement. Les raisonneurs traditionnels sont trop lourds en termes d'empreinte mémoire et/ou de temps de calcul pour pouvoir être implémentés sur de petits objets. LiRoT est un raisonneur léger et incrémental qui peut être embarqué sur des objets contraints, rendant possible le raisonnement au sein d'une architecture fog. L'objectif principal de ce travail est de réduire l'empreinte mémoire du raisonnement tout en ayant un impact minimal sur le temps de calcul ; les techniques d'optimisation habituelles ne sont pas adaptées
Line-field confocal optical coherence tomography based on tandem interferometry with a focus-tunable lens
No full textInternational audienceThis article introduces an innovative line-field confocal optical coherence tomography (LC-OCT) system based on tandem interferometry, featuring a focus-tunable lens for dynamic focusing. The principle of tandem interferometry is first recalled, and an analytical expression of the interferometric signal detected is established in order to identify the influence of key experimental parameters. The LC-OCT system is based on a Linnik-type imaging interferometer with a focus-tunable lens for focus scanning, coupled to a Michelson-type compensating interferometer using a piezoelectric linear translation stage for coherence plane scanning. The system achieves axial and lateral image resolutions of approximately 1 µm over the entire imaging depth (400 µm), in line with conventional LC-OCT. Vertical section images (B-scans) of skin acquired at 14.3 fps reveal distinguishable structures within the epidermis and dermis. Using refocusing and stitching, images of a tissue phantom were obtained with an imaging depth superior to 1.4 mm. The system holds promise for LC-OCT miniaturization, along with enhanced imaging speed and extended imaging depth
Color effects based on resonant waveguide grating embedded in a luminescent sol-gel layer
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QOSST: A Highly Modular Open Source Platform for Continuous Variable Quantum Key Distribution Applications
No full textInternational audienceWe present a highly modular Open Source Software to perform CV-QKD experiments. The software is hardware agnostic and was benchmarked on bulk and integrated receivers, reaching state of the art secret key rates