Sources paramétriques optiques et applications

Ce mémoire de HDR reprend les activités de recherche que j’ai menées à l’Onera. Le fil directeur de ces travaux est la compréhension et la mise en œuvre d’effets d’optique non linéaire pour la réalisation de sources et de fonctions optiques ayant principalement vocation à être intégrées dans des instruments de métrologie optique. Les applications visées concernent plus particulièrement la détection et l’analyse de gaz par des mesures locales ou à distance.Ces différentes activités sont regroupées selon cinq thématiques correspondant chacun à un chapitre différent :- Le premier chapitre est dédié aux développements portant sur les oscillateurs paramétriques optiques (OPO) à filtrage par effet Vernier et leurs mises en application, en particulier pour les applications de détection et d’analyse de gaz.- Le deuxième chapitre décrit d’autres développements d’architectures d’OPO originales utilisant les spécificités de l’interaction paramétrique. - Le troisième chapitre présente les travaux sur les sources paramétriques optiques infrarouges à base de matériaux semi-conducteurs. - Le quatrième chapitre est dédié à la thématique des fonctions et sources optiques non linéaires ultra-rapides.- Le cinquième chapitre porte sur les activités plus fondamentales de caractérisation des corrélations de photons par absorption à deux photons dans les semi-conducteurs

Tunable Narrowband Tm:YAP Laser using a Transversally Chirped Volume Bragg Grating

International audienceTunable long wave infrared (LWIR) coherent sources emitting between 8 and 12 μm can be used for versatile remote gas sensing. In ref [1] we implemented a parametric oscillator in which wavelength tunability was achieved by temperature tuning of the crystal indices of refraction. It is well known that a similar wavelength range can be addressed by tuning the pump wavelength rather than the crystal temperature [2]. In addition, pump tuning can be significantly faster than temperature tuning. In this context we also need a narrow band spectrum to control the spectral output of the optical parametric oscillator, which is based on Vernier spectral filtering in doubly-resonant cavities. Seger and his team exhibited single longitudinal mode operation in a microlaser tuned with transversally chirped volume Bragg grating (TC-VBG) near 1 μm [3]. We show how this concept can be applied to a different laser emitting at 2 μm

Parametric Sources for Chemicals and Gas Sensing

International audienceWe present our activities on the development of tunable optical parametric sources for gas sensing. In particular, we introduce the nested cavity OPO, and rapidly tunable OPOs based on aperiodic quasi-phase matching

Thermal effects in a single-frequency, fiber laser pumped, nested cavity optical parametric oscillator

International audienceWe investigate thermal effects in a nested-cavity doubly resonant optical parametric oscillator (NesCOPO), pumped by a high repetition rate laser, and the consequences on its spectral characteristics

Quartz Enhanced Photoacoustic Spectroscopy Based on a Custom Quartz Tuning Fork.

We have designed and fabricated a custom quartz tuning fork (QTF) with a reduced fundamental frequency; a larger gap between the prongs; and the best quality factor in air at atmospheric conditions ever reported, to our knowledge. Acoustic microresonators have been added to the QTF in order to enhance the sensor sensitivity. We demonstrate a normalized noise equivalent absorption (NNEA) of 3.7 × 10-9 W.cm-1.Hz-1/2 for CO₂ detection at atmospheric pressure. The influence of the inner diameter and length of the microresonators has been studied, as well as the penetration depth between the QTF's prongs. We investigated the acoustic isolation of our system and measured the Allan deviation of the sensor

The NAOMI GAZL multispecies differential absorption lidar: realization and testing on the TADI gas leak simulation facility

International audienceWe report on a differential absorption lidar, designed for remote detection of CH 4 and CO 2 , based on a single-frequency 1.57-1.65 µm parametric oscillator/amplifier system. The lidar is tested on a controlled gas release facility

Closed-loop separation control over a sharp edge ramp using Genetic Programming

We experimentally perform open and closed-loop control of a separating turbulent boundary layer downstream from a sharp edge ramp. The turbulent boundary layer just above the separation point has a Reynolds number $Re_{\theta}\approx 3\,500$ based on momentum thickness. The goal of the control is to mitigate separation and early re-attachment. The forcing employs a spanwise array of active vortex generators. The flow state is monitored with skin-friction sensors downstream of the actuators. The feedback control law is obtained using model-free genetic programming control (GPC) (Gautier et al. 2015). The resulting flow is assessed using the momentum coefficient, pressure distribution and skin friction over the ramp and stereo PIV. The PIV yields vector field statistics, e.g. shear layer growth, the backflow area and vortex region. GPC is benchmarked against the best periodic forcing. While open-loop control achieves separation reduction by locking-on the shedding mode, GPC gives rise to similar benefits by accelerating the shear layer growth. Moreover, GPC uses less actuation energy.Comment: 24 pages, 24 figures, submitted to Experiments in Fluid

Comprendre. Détection de gaz par spectroscopie photoacoustique : principe et mise en œuvre

International audienceLa spectroscopie photoacoustique permet la détection de gaz à l’état de traces. Cette technique permet d’allier compacité, sensibilité, rapidité et grande bande passante optique. Pour ces raisons, elle a le potentiel d’être intégrée dans des instruments permettant de répondre à de multiples enjeux liés à l’environnement, la défense, et la sûreté