New signal processing for fast and accurate QEPAS measurements

International audienceQuartz Enhanced Photoacoustic Spectroscopy (QEPAS) gas sensors have been widely developed over the last decade. This technique takes advantage of a high quality factor micro tuning fork to enable high detectivity & high selectivity miniature gas sensors. Lock-in detection technique is classically used to measure the resonator amplitude proportional to gas concentration, but this technique is slow and does not follow the resonator frequency shift over temperature. This paper presents a new QEPAS signal processing technique that allows faster and more accurate measurements that will enable accurate and fast multi gas sensors

Coherent combining of mid-infrared difference frequency generators

International audienceWe report what is, to the best of our knowledge, the first experimental demonstration of coherent combining of two mid-infrared difference frequency generators by active phase control in continuous-wave regime. Using the phase relation that is inherent to the nonlinear process, we are able to phase-lock and combine the idler waves by the sole phase control of one of the pump waves. This control is done by an all fiber electro-optic modulator. Combining is achieved with an excellent efficiency with a residual phase error of λ/28

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

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

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

Mise en forme spectrale et temporelle de sources optiques infrarouges par mélange non-linéaire à trois ondes

Because they use a resonant process, lasers are often hindered by the small number of available wavelengths and their narrow tunability. Fortunately, nonlinear optics allows to go beyond these limitations by doing frequency conversion in a non resonant way. It is now used in optical parametric oscillators (OPOs) to cover the whole optical spectrum with a wide tunability. However, OPOs display unique properties : three coupled waves with different frequencies and group velocities, a power and phase dependent amplification, and no energy storage. In this work we show that these properties lead to new designs of nonlinear optical sources. We begin with an OPO with increased efficiency, implementing two KTA crystals pumped at 1,064 μm in the nanosecond regime. We then study the possibility of generating short pulses directly in a cw-pumped OPO. We show for the first time that active modelocking in an OPO is possible in the steady-state regime. We then propose to implement passive modelocking by a saturabler absorber in an cw-pumped OPO where there is a strong group velocity mismatch between the signal and the pump. Finally, we adress optical sources including a laser medium and a nonlinear crystal. We build a nonlinear mirror using a PPLN crystal and insert it in a Cr:ZnSe laser to produce picosecond pulses by passive modelocking. We also discuss the possibility of including an OPO inside a cw laser, to produce short tunable pulses in the mid-infrared.Pour certaines applications, les lasers offrent un choix trop restreint de longueurs d'ondes, et une faible accordabilité. Ces limitations viennent du fait que l'effet laser utilise des résonances atomiques. L'optique non-linéaire permet de s'en affranchir c'est un phénomène non résonnant, donc peu sélectif en longueur d'onde. Néanmoins elle présente des caractéristiques particulières : trois fréquences différentes mises en jeu, l'absence de stockage d'énergie, et le rôle primordial de la phase relative entre les ondes. Dans ce travail nous mettons à profit ces specificités pour mettre en forme spectralement ou temporellement l'émission de lumière dans des sources infrarouges. La première source réalisée est un oscillateur paramétrique optique (OPO) à 3 μm utilisant deux cristaux de KTA. Ses performances sont discutées en régime nanoseconde. Puis nous réalisons un OPO à cristal de PPLN générant des impulsions courtes sous pompage continu par modulation active des pertes. Nous proposons ensuite d'utiliser un absorbant saturable pour verrouiller passivement les modes d'un OPO continu présentant un fort désaccord de vitesse de groupe entre la pompe et le signal. Enfin, nous considérons le cas des sources intégrant à la fois un milieu laser et un dispositif non-linéaire. Nous présentons d'abord un miroir non-linéaire à base de PPLN intégré dans un laser Cr:ZnSe, permettant de produire des impulsions picosecondes accordables autour de 2,5 μm. Nous proposons ensuite de généraliser ce principe en intégrant un OPO dans un laser afin de réaliser une source ultrabrève compacte et accordable

Mise en forme spectrale et temporelle de sources optiques infrarouges par mélange non-linéaire à trois ondes

PALAISEAU-Polytechnique (914772301) / SudocSudocFranceF

Optical parametric oscillators

Optical parametric oscillators are versatile devices for generating a tunable coherent radiation from an incident laser beam. They rely on nonlinear frequency conversion to cover spectral ranges that are poorly or not covered by direct laser emission. This article presents a short overview of the optical parametric oscillators principles of operation, main implementations and related applications