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Recovering particle velocity and size distributions in ejecta with Photon Doppler Velocimetry
No full textInternational audienceWhen a solid metal is struck, its free surface can eject fast and fine particles. Despite the many diagnostics that have been implemented to measure the mass, size, velocity or temperature of ejecta, these efforts provide only a partial picture of this phenomenon. Ejecta characterization, especially in constrained geometries, is an inherently ill-posed problem. In this context, Photon Doppler Velocimetry (PDV) has been a valuable diagnostic, measuring reliably particles and free surface velocities in the single scattering regime. Here we present ejecta experiments in gas and how, in this context, PDV allows one to retrieve additional information on the ejecta, i.e. information on the particles' size. We explain what governs ejecta transport in gas and how it can be simulated. To account for the multiple scattering of light in these ejecta, we use the Radiative Transfer Equation (RTE) that quantitatively describes PDV spectrograms, and their dependence on the velocity but also on the size distribution of the ejecta. We remind how spectrograms can be simulated by solving numerically this RTE and we show how to do so on hydrodynamic ejecta simulation results. Finally, we use this complex machinery in different ejecta transport scenarios to simulate the corresponding spectrograms. Comparing these to experimental results, we iteratively constrain the ejecta description at an unprecedented level. This work demonstrates our ability to recover particle size information from what is initially a velocity diagnostic, but more importantly it shows how, using existing simulation of ejecta, we capture through simulation the complexity of experimental spectrograms
Effects of Pt doping on surface properties and quenching of band edge emission in ZnO
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Numerical simulations for the SAXO+ upgrade: Performance analysis of the adaptive optics system
No full textInternational audienceContext. SPHERE, operating at the VLT since 2014, is currently one of the high-contrast instruments with a higher performance. Its adaptive optics system, known as SAXO, will be upgraded to SAXO+, which features the addition of a second stage of adaptive optics. This stage will use a near-infrared pyramid wavefront sensor to record images of fainter exoplanets around redder stars. Aims. In this work, we compare the performance of SAXO and SAXO+. We look for the optimal values of the key system parameters of SAXO+ for various science cases and turbulence conditions. Methods. We performed numerical simulations using COMPASS, an end-to-end adaptive optics simulation tool. We simulated perfect coronagraph images of an on-axis point source, and we minimized the residual starlight intensity between 3 and 5 λ/D as a performance criterion. The explored parameter space includes science cases (described by magnitude in G and J bands), turbulence conditions (seeing and coherence time), and key system parameters (first and second stage gains, first and second stage frequencies, pyramid modulation radius, pyramid modal gains optimization). Results. In every science case and turbulence condition, SAXO+ reduces the residual starlight intensity inside the correction zone of the second stage by a factor of ten compared to SAXO. The optimal first stage gain is lower for SAXO+ than for SAXO alone. We quantified the gain in performance of SAXO+ when changing the second stage frequency from 2 to 3 kHz, and we conclude that 2 kHz may be sufficient for most realistic conditions. We give the optimal first stage gain as well as the first and second stage frequencies for every seeing, coherence time, and science case. Finally, we find that a 2 λ WFS / D pyramid modulation radius is a good trade-off between performance and robustness against varying turbulence conditions. Conclusions. This study shows that the future SAXO+ system will outperform the current SAXO system in all studied cases
SAR image synthesis using text conditioned pre-trained generative AI models
No full textInternational audienceWe explore the utilization of artificial intelligence (AI) generative models for creating high-resolution airborne Synthetic Aperture Radar (SAR) images. Our methodology involves the use of a text-conditioned latent diffusion architecture to train a generative model. We use a database of high-resolution SAR images obtained from the SETHI sensor at ONERA for training purposes. This model is capable of generating synthetic images based on textual prompts provided by users. Additionally, we illustrate the model's versatility for various applications, such as generating SAR images from handdrawn sketches
Optimization of a freeform TMA with a differential ray tracer with NURBS capabilities
No full textInternational audienceOptimizing freeform systems can encounter convergence difficulties due to the many degrees of freedom that these surfaces bring to optical systems. Moreover, the description of these freeform surfaces in a polynomial basis may impose prior knowledge on the shape of the surface. In this presentation, we will showcase a differential ray tracer with NURBS capabilities called FORMIDABLE. In contrast to available commercial optical design software, such as Zemax OpticStudio and Synopsys Code V, this library i can simulate and especially optimize Non-Uniform Rational B-Spline (NURBS) surfaces. The key advantage of NURBS lies in their ability to locally describe an optical surface, thereby minimizing preconceived notions about the surface shape, aside from the surface sampling determined by the density of the NURBS representation. The main drawback, however, is the significant increase in the degrees of freedom within the optical system, making the optimization of these surfaces a complex task with a conventional commercial optical design software. FORMIDABLE's implementation of differential ray-tracing capabilities allows faster convergence of systems described by many degrees of freedom and makes optimization with NURBS surfaces viable. The features of FORMIDABLE will first be described. Then its capabilities will be illustrated with the optimization of a classical nonreimaging Three-Mirror Anastigmat (TMA) by considering either a description of surfaces by NURBS or a description by the polynomial basis XY. Then, this optimized TMA will be compared with its equivalent optimized with Zemax OpticStudio. To enable this software comparison, we will use the same starting point and practically the same merit function. Standard metrics, such as Root Mean Square (RMS) spot size across the field of view (FOV) will be used to assess the imaging quality
Silicon Solid-state Detector for Characterization of Thermal Neutrons in the Accelerator Radiation Environment
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Highly uniform silicon nanopatterning with deep-ultraviolet femtosecond pulses
No full textInternational audienceThe prospect of employing nanophotonic methods for controlling photon-electron interactions has ignited substantial interest within the particle accelerator community. Silicon-based integrated dielectric laser acceleration (DLA) has emerged as a viable option by leveraging localized photonic effects to emit, accelerate, and measure electron bunches using exclusively light. Here, using highly regular nanopatterning over large areas while preserving the crystalline structure of silicon is imperative to enhance the efficiency and yield of photon-electron effects. While several established fabrication techniques may be used to produce the required silicon nanostructures, alternative techniques are beneficial to enhance scalability, simplicity and costefficiency. In this study, we demonstrate the nano-synthesis of silicon structures over arbitrarily large areas utilizing exclusively deep ultraviolet (DUV) ultrafast laser excitation. This approach delivers highly concentrated electromagnetic energy to the material, thus producing nanostructures with features well beyond the diffraction limit. At the core of our demonstration is the production of silicon laser-induced surface structures with an exceptionally high aspect-ratio -reaching a height of more than 100 nm-for a nanostructure periodicity of 250 nm. This result is attained by exploiting a positive feedback effect on the locally enhanced laser electric field as the surface morphology dynamically emerges,</div
Pre-irradiation Influence on Proton Radioluminescence Responses of Sol-gel Optical Fibers
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VERS DES SECTIONS EFFICACES D'ABSORPTION DE HAUTE PRÉCISION AUTOUR DE 308 NM POUR LA DÉTECTION À DISTANCE DE L'OZONE ATMOSPHÉRIQUE
No full textInternational audienceAtmospheric ozone amount measurements in the atmosphere strongly depend on spectroscopic data in the UV and other wavelength ranges. Recently, the ozone absorption cross section at 253.65 nm used in standard reference photometers (SRPs) for the calibration of ambient ozone photometers has been re-evaluated and a new value was recommended [1]. Within experimental uncertainty, this new value is in agreement with current recommendations of UV-VIS absorption cross sections to be used for atmospheric remote sensing of ozone [2]. High precision laboratory measurements at 325 nm, however, possibly indicate that currently recommended cross sections might be biased by some percent in the Huggins band region [3]. Since this wavelength region is used by a number of ozone measurement platforms such as stratospheric LIDARs (at 308 nm), Brewer and Dobson spectrophotometers in the range, and various satellite missions, we propose new accurate measurements in the 308 nm - 320 nm region. A UV spectroscopic system based on a narrow tunable laser for the 307.8 nm - 308.2 nm range and on a broadly tunable 308 nm – 318 nm laser is presented. It targets an ozone absorption cross section uncertainty of better than 1% at temperatures between -90°C and +30°C. The impact on the accuracy of stratospheric lidar measurements [4] is discussed.This work is funded by the French ANR under grant number ANR-22-CE01-0007.[1] Hodges et al., Metrologia 56, 034001 (2019). Doi : 10.1088/1681-7575/ab0bdd[2] Orphal et al., J. Mol. Spectrosc. 327, 105-121 (2016). Doi: 10.1016/j.jms.2016.07.007[3] Janssen et al., Atmos. Meas. Tech. 11, 1707-1723 (2018). Doi: 10.5194/amt-11-1707-2018[4] Leblanc et al., Atmos. Meas. Tech. 9, 4051-4078 (2016). Doi: 10.5194/amt-9-4051-2016Les mesures de la quantité d'ozone atmosphérique dans l'atmosphère dépendent fortement des données spectroscopiques dans l'UV et d'autres gammes de longueurs d'onde. Récemment, la section efficace d'absorption de l'ozone à 253,65 nm utilisée dans les photomètres de référence standard (SRP) pour l'étalonnage des photomètres d'ozone ambiant a été réévaluée, et une nouvelle valeur a été recommandée [1]. Dans l'incertitude expérimentale, cette nouvelle valeur est en accord avec les recommandations actuelles des sections efficaces d'absorption UV-VIS à utiliser pour la télédétection atmosphérique de l'ozone [2]. Cependant, des mesures de haute précision en laboratoire à 325 nm indiquent que les sections efficaces actuellement recommandées pourraient être biaisées de quelques pour cent dans la région de la bande de Huggins [3]. Comme cette région de longueurs d'onde est utilisée par un certain nombre de plateformes de mesure de l'ozone, telles que les lidars stratosphériques (à 308 nm), les spectrophotomètres Brewer et Dobson dans cette gamme, ainsi que diverses missions satellites, nous proposons de nouvelles mesures précises dans la région de 308 nm à 320 nm. Un système spectroscopique UV basé sur un laser accordable étroit pour la gamme de 307,8 nm à 308,2 nm et sur un laser accordable large de 308 nm à 318 nm est présenté. Il vise une incertitude de la section efficace d'absorption de l'ozone inférieure à 1 % à des températures comprises entre -90°C et +30°C. L'impact sur la précision des mesures lidar stratosphériques [4] est discuté.Ce travail est financé par l'ANR française sous le numéro de subvention ANR-22-CE01-0007.[1] Hodges et al., Metrologia 56, 034001 (2019). DOI : 10.1088/1681-7575/ab0bdd [2] Orphal et al., J. Mol. Spectrosc. 327, 105-121 (2016). DOI : 10.1016/j.jms.2016.07.007 [3] Janssen et al., Atmos. Meas. Tech. 11, 1707-1723 (2018). DOI : 10.5194/amt-11-1707-2018 [4] Leblanc et al., Atmos. Meas. Tech. 9, 4051-4078 (2016). DOI : 10.5194/amt-9-4051-201
CARACTÉRISATION D’UNE SOURCE LASER UV ACCORDABLE A 308 NM POUR LA SPECTROSCOPIE DE L'OZONE
No full textInternational audienceAtmospheric ozone measurements are largely influenced by spectroscopic data covering various spectral ranges, particularly in the UV. Laboratory measurements conducted at 325 nm suggest that the currently recommended cross-sections for atmospheric sounding may be biased by a few percent in the Huggins band region [1]. Since this wavelength range is used by various ozone measurement platforms, such as stratospheric LIDAR at 308 nm, Brewer and Dobson spectrophotometers, and various satellite missions, we propose to revisit the ozone cross-section in this spectral range using a laser method. Laser spectroscopy enables spectral resolution and frequency control that are difficult to achieve with traditional spectroscopic methods.We envision a study based on two different laser systems. The first source is configured with a narrow range from 307.8 nm to 308.2 nm, suitable for stratospheric LIDAR applications. The second source is designed to be broadly tunable between 308 nm and 318 nm, making it suitable for spectroscopic measurements and enabling extensive exploration of the spectral range.The current presentation will focus on the first system. Using Sum Frequency Generation (SFG) techniques, the laser system can emit monochromatic light in the wavelength range from 307.8 nm to 308.2 nm. We will present the system setup and characterize its tunability, spectral resolution, and power. The UV source is generated by frequency summing a blue laser at 441.6 nm and a tunable infrared laser source around 1 µm. The output power of the latter is amplified using a Ytterbium-doped fiber amplifier. The two signals are combined with a dichroic mirror, and the frequency sum is generated with a BBO crystal.Our goal is to achieve an uncertainty in the ozone absorption cross-section of less than 1%, which will help reduce uncertainties in the ozone molecule cross-sections in this wavelength range.This work was supported by the ANR (ALPHA-O3 project, under number ANR-22-CE01-0007) and the national LEFE (Les Enveloppes Fluides et l'Environnement) program of INSU-CNRS.[1] Janssen et al., Atmos. Meas. Tech. 11, 1707-1723 (2018). Doi: 10.5194/amt-11-1707-2018Les mesures de l'ozone atmosphérique sont largement influencées par les données spectroscopiques couvrant diverses gammes spectrales, en particulier dans l'UV. Des mesures de laboratoire réalisées à 325 nm laissent suggérer que les sections efficaces actuellement recommandées pour le sondage atmosphérique pourraient être biaisées de quelques pourcents dans la région de la bande de Huggins [1]. Étant donné que cette région de longueur d'onde est utilisée par différentes plates-formes de mesure de l'ozone, telles que les LIDAR stratosphériques à 308 nm, les spectrophotomètres Brewer et Dobson, et diverses missions satellitaires, nous proposons de revisiter la section efficace de l’ozone dans cette gamme spectrale par méthode laser. La spectroscopie laser permet d’obtenir une résolution spectrale et un contrôle de fréquence difficilement atteignable avec des méthodes spectroscopiques traditionnelles.Nous envisageons une étude basée sur deux systèmes laser différents. La première source est configurée avec une plage étroite de 307.8 nm à 308.2 nm, adaptée aux applications du LIDAR stratosphérique. Quant à la seconde source, elle est conçue pour être largement accordable entre 308 nm et 318 nm, ce qui la rend adaptée pour les mesures spectroscopiques et permet une exploration étendue de la gamme spectrale.La présentation actuelle ciblera le premier système. En utilisant des techniques de génération de somme de fréquences (SFG), le système laser est capable d'émettre de la lumière monochromatique dans une gamme de longueurs d'onde allant de 307.8 nm à 308.2 nm. Nous présenterons le montage du système et en caractériserons l'accordabilité, la résolution spectrale et la puissance. La source UV est réalisée par somme de fréquence d’un laser bleu à 441.6 nm et une source laser accordable dans l'infrarouge autour de 1µm. La puissance de sortie de cette dernière est amplifiée grâce à un amplificateur à fibre dopée Ytterbium. Les deux signaux sont combinés avec une lame dichroïque, et la somme de fréquence est réalisée avec un cristal de BBO.Notre objectif est de parvenir à une incertitude sur la section efficace d'absorption de l'ozone inférieure à 1 % ce qui permettra de réduire les incertitudes des sections efficaces des molécules d'ozone dans cette gamme de longueurs d’onde. Ce travail a bénéficié du soutien de l'ANR (projet ALPHA-O3, sous numéro ANR-22-CE01-0007) et du programme national LEFE (Les Enveloppes Fluides et l'Environnement) de l'INSU-CNRS.[1] Janssen et al., Atmos. Meas. Tech. 11, 1707-1723 (2018). Doi: 10.5194/amt-11-1707-201