Measures de vent 3D avec le lidar Doppler coherent Live à bord d'un avion

International audienceA three-dimensional (3D) wind profiling Lidar, based on the latest high power 1.5 µm fiber laser development at Onera, has been successfully flown on-board a SAFIRE (Service des Avions Français Instrumentés pour la Recherche en Environnement) ATR42 aircraft. The Lidar called LIVE (LIdar VEnt) is designed to measure wind profiles from the aircraft down to ground level, with a horizontal resolution of 3 km, a vertical resolution of 100 m and a designed accuracy on each three wind vector components better than 0.5 m.s −1. To achieve the required performance, LIVE Lidar emits 410 µJ laser pulses repeating at 14 KHz with a duration of 700 ns and uses a conical scanner of 30 • total opening angle and a full scan time of 17 s.Un lidar vent 3D, basé sur le dernier développement de laser à fibre de 1,5 µm à haute puissance de l’ONERA a été testé avec succès à bord d’un avion SAFIRE ATR42. Le lidar appelé LIVE est conçu pour mesurer les profils de vent de l’avion jusqu'au sol, avec une résolution horizontale de 3 km, une résolution verticale de 100 m et une précision calculée supérieure à 0,5 m / s pour chaque composante du vecteur du vent

Workshop Report - WP4 Volvic Case Study. Pegasus, H2020 project, Grant agreement No 633814

Workshop Report - WP4 Volvic Case Study. Pegasus, H2020 project, Grant agreement No 633814, 53 pages and annex

Audit sur l’activité de conseil architectural du Parc naturel régional du Pilat: Premières pistes pour le futur du Conseil en Architecture

Premières pistes pour le futur du Conseil en Architectur

After 10’000 years of movements, is the La Frasse landslide stabilized? Numerical modeling of the crises of a large landslide and of its mitigation measures

Using advanced hydro-geological and geo-mechanical finite element simulations, it has been possible to model the behavior of a large slope movement, namely the La Frasse landslide in Switzerland. The slide experiences a permanent movement of about 10 to 15 cm/year in its central part and recurrent crises in its more active lower part. The pore water pressure fields corresponding to the 1994 crisis were first calculated with a hydrogeological model and then implemented in a geo-mechanical model. The various site investigations that were carried out consecutively to the previous crises of the slide or in order to calibrate the numerical model are also presented. The model is finally tuned to assess the efficiency of a drainage gallery. The comparison between the drainage gallery as modeled and as constructed is also presented

Combinaison cohérente de générateurs de différence de fréquences : démonstration expérimentale et application aux oscillateurs paramétriques optiques

International audienceCoherent beam combining (CBC) by active phase control could be useful for power scaling fiber-laser-pumped optical frequency converters like optical parametric oscillators (OPOs). We developed an indirect phase control approach based on the phase matching relation intrinsic to efficient nonlinear processes. Previously, we demonstrated coherent combining of second harmonic waves through real time active control of the phases of the fundamental waves, using high bandwidth fibered electro-optic phase modulators. In the case of this 2-wavelength process, it was possible to simultaneously combine both the fundamental and the second harmonic waves. In this paper, we present an experimental demonstration of coherent combining of difference frequency generators emitting an idler wave at 3400 nm. We confirm experimentally the theoretical prediction that through active phase control of the sole 1064 nm pump waves, it's possible to coherently combine the idler waves efficiently. A residual phase error of 1/28th wave at 3400 nm is achieved, corresponding to an excellent combining efficiency. However, in such a 3-wavelength process, simultaneous combination of the signal and idler waves is not always feasible. This demonstration opens the way to mid-infrared OPO combining. We present the architectures of continuous wave OPOs we are working on.Nous présentons une démonstration expérimentale de combinaison cohérente de générateurs de différence de fréquences émettant à 3400 nm. Nous montrons que par le contrôle actif de la phase des seules ondes de pompe à 1064 nm, il est possible de réaliser la combinaison cohérente efficace des ondes complémentaires, avec une différence de phase résiduelle de lambda/28. Nous présentons aussi les architectures d’OPO continus sur lesquelles nous travaillons, ainsi que les premiers résultats de combinaison cohérente de ces OPOs. Nous détaillons comment les modes de cavité des OPOs combinés sont mis en coïncidence, et comment le contrôle actif de la phase utilisé pour la combinaison de DFG peut être mis en œuvre dans ce cas

Coherent combining of optical parametric oscillators: challenges and experimental demonstrations

International audienceCoherent combining (CBC) techniques are very efficient to power scale lasers to the multikilowatt level. However, high power fiber lasers are only available within a finite set of wavelengths, mainly amongst 1 µm, 1.5 µm and 2 µm. Hopefully, nonlinear crystals offer the capability to convert these laser lines to access higher wavelengths in the midinfrared bands, for instance between 3 and 5 µm. In this paper, we present the challenges of applying coherent combining by active phase control to much more powerful frequency converters: optical parametric oscillators (OPO). An experimental demonstration of OPO CBC is also detailed.Les techniques de combinaison cohérente sont très efficaces pour monter en puissance les lasers jusqu'à plusieurs kilowatts. Cependant, les lasers à fibres forte puissance sont uniquement disponibles à certaines longueurs d'onde précises, 1 micron, 1,5 microns ou 2 microns. Par chance, les cristaux non linéaires offrent la possibilité de convertir ces longueurs d'onde laser vers le moyen infrarouge entre 3 et 5 microns.Dans cet article, nous présentons les défis de la mise en oeuvre de la combinaison cohérente par contrôle actif de la phase pour des convertisseurs de fréquence plus forte puissance: les oscillateurs paramétriques optiques (OPO). Une démonstration expérimentale de combinaison cohérente d'OPO est aussi présentée

Raman lidar for hydrogen gas concentration monitoring and future radioactive waste management

International audienceA multi-channel Raman lidar has been developed, allowing for the first time simultaneous and high-resolution profiling of hydrogen gas and water vapor. The lidar measures vibrational Raman scattering in the UV (355 nm) domain. It works in a high-bandwidth photon counting regime using fast SiPM detectors and takes into account the spectral overlap between hydrogen and water vapor Raman spectra. Measurement of concentration profiles of H2 and H2O are demonstrated along a 5-meter-long open gas cell with 1-meter resolution at 85 meters. The instrument precision is investigated by numerical simulation to anticipate the potential performance at longer range. This lidar could find applications in the French project Cigéo for monitoring radioactive waste disposal cells

All-fibered coherent-differential absorption lidar at 1.645 μm for simultaneous methane and wind-speed measurements

International audienceHere we report on the development of a new coherent-DIAL system as well as first quantitative measurements of simultaneous gas mixing ratio and radial wind-speed with the instrument. Integrated measurement of atmospheric methane (CH4) mixing ratio between the instrument and a hard-target located at 2:25 km has been conducted with a relative precision of nearly 20% in 17 s. The measurement procedure also gives information on integrated water vapor (H2O) mixing ratio

En camino hacia la mejora continua de procesos

International audienceSome applications like range finding, optical counter measures or engine ignition, require lasers capable of delivering high repetition rate bursts of nanosecond pulses with hundreds of microjoules to a few millijoules in terms of energy per pulse. We have developed such a diode pumped Yb:YAG micro-laser with an oscillator comprised of a 2-mm long 10% at. doped Yb:YAG crystal followed by a Cr:YAG passive Q-switch with an initial transmittance of 85 %. The laser plano-concave cavity is 5-cm long. This oscillator emits 250 µJ to 300 µJ per pulse, with a 3-5 ns pulse duration, with an intra-burst pulse repetition frequency that can be tuned continuously from 1 kHz to 20 kHz by increasing the pump power. The pumping diode laser is operated in quasi continuous wave regime, emitting 1-ms to 10-ms long pulses with up to 20 W peak power This qcw pumping results in the emission of a burst of pulses at high repetition rate for the duration of this pump long pulse. These pump pulses, and consequently the bursts of nanosecond pulses, are repeated at very low frequency, between 1 Hz and 5 Hz, so that the average power to handle doesn't require active cooling. This oscillator is then amplified to the millijoule level in a second 3-mm long Yb:YAG crystal pumped by a synchronous qcw emitting diode laser.Nous avons développé un micro-laser Yb:YAG pompé par diode et déclenché passivement par un cristal de Cr:YAG, qui délivre des paquets d’impulsions nanoseconde avec des énergies par impulsions de l’ordre du millijoule.L’oscillateur émet autour de 300 µJ par impulsion, avec une durée d’impulsion de quelques nanosecondes, dont la cadence à l’intérieur du paquet d’impulsions peut être accordée continûment jusqu’à 20 kHz. Il est amplifié jusqu’au millijoule par un second cristal d’Yb:YAG pompé par diode laser. Les diodes laser de pompe sont synchrones et fonctionnent en régime quasi continu. Elles émettent des pulses longs répétés à seulement quelques hertz, de façon à ne pas nécessiter de refroidissement actif

'Les Sacoches du Climat': An outreach cycling initiative for covering the last mile of climate communication in rural France

International audienceRural and medium-sized town populations already regularly face the tangible impacts of climate change, particularly in relation to their professional activities. However, they are often overlooked by the scientific community when it comes to knowledge sharing, even though they equally deserve attentive listening and consideration. 'Les Sacoches du Climat' (i.e. 'The Climate Panniers') is a French scientific outreach initiative led by a collective of young climate researchers specializing in various fields. The initiative was designed to raise awareness of climate issues in such regions, taking on the challenge of reaching the last mile in the large-scale French awareness campaign 'La Tournée du Climat et de la Biodiversité' (i.e. 'The Climate and Biodiversity Tour') — a traveling exhibition in major cities addressing climate and biodiversity issues led by a multidisciplinary team of scientists. Our journey unfolded over a week, navigating the landscapes of rural France on bicycles. During the day, we engaged with secondary school audiences, delivering an introduction to climate challenges followed by interactive discussions and workshops, with a particular emphasis on a sensitive approach. This educational endeavor was seamlessly intertwined with collaborative projects involving teaching staff. In the evening, we engaged adult audiences through conferences and debates, fostering collaboration with local communities and associations. Accompanied by esteemed French climatologists riding tandem with us, our collective presents here a brief retrospective of this journey and the messages derived from it. This initiative serves as an earnest call for climatologists to step beyond the traditional confines of research, immerse themselves in the field, and consider the impacts, adaptation, and vulnerability of territories in all their diversity and specificity in the face of climate change, fostering a responsible societal paradigm shift