Intracavity absorption spectroscopy with a turbulent detuned actively mode-locked Ti:sapphire laser

International audienceIntracavity laser absorption spectroscopy (ICLAS) is an extremely sensitive method for the detection of very weak absorptions. However, the conventional use of multimode lasers has thus far significantly reduced its ability to detect in situ molecules and its sensitivity. We propose the use of a new type of laser that overcomes these limitations: the turbulent detuned actively mode-locked (TDAM) Ti:sapphire laser, which owing to its short coherence length, eliminates harmful intracavity interferences. The proposed technique called TDAM-ICLAS is furthermore highly sensitive to intracavity absorption, continuously tunable and has no frequency chirp

Statistical properties of frequency shifted feedback lasers

International audienceWe evidence experimentally the statistical properties of frequency shifted feedback (FSF) lasers through measurements of the homodyne beat signal and interferometric autocorrelation of a dye FSF laser at the output of a Michelson interferometer. The FSF laser is found to show thermal fluctuations and photon bunching. Moreover whereas the degree of first-order coherence vanishes beyond the coherence length of the FSF source, the degree of second-order coherence exhibits periodic revivals far beyond the coherence length, with a period equal to the cavity roundtrip time. Our observations are in good agreement with the theoretical treatment of Yatsenko et al. [L.P. Yatsenko, B.W. Shore, K. Bergmann, Opt. Comm. 236 (2004) 183] and validate the description of the output field of a FSF laser by a broadband cyclostationary thermal field

λ/2 fringe-spacing interferometer

International audienceThe precision of interferometry is directly linked to the fringe spacing of the recorded interferogram. Whereas all interferometric devices show a fringe spacing equal to a wavelength of the laser light we present a novel scheme of a two-beam interferometer exhibiting a fringe spacing reduced by a factor of 2; the direct detection of the beat signal is replaced with the monitoring of the fluorescence of a twofold degenerate atomic system resonant with the laser. The λ/2 fringe spacing in the fluorescence signal is demonstrated with a hot sodium vapor excited by a broadband laser tuned to the D1 line. In the saturation regime, the dark fringes are expected to be extremely narrow, leading to the possibility of nanoscale displacement measurements or atom localization

Coherence properties of modeless lasers

International audienceMost of classical light sources show a close similarity between their first and second order correlation functions (resp. g(1) and g(2)) functions. We present here the original coherence properties of a peculiar type of laser named modeless laser or Frequency Shifted Feedback (FSF) laser where the g(1) and g(2) functions show a different behaviour. We calculate and evidence experimentally the first and second order correlation functions of modeless lasers, through measurements of the homodyne beat signal and interferometric autocorrelation of a dye FSF laser at the output of a Michelson interferometer. Whereas the degree of first-order coherence vanishes beyond the coherence length of the FSF source, the degree of second-order coherence exhibits periodic revivals far beyond the coherence length, with a period equal to the cavity roundtrip time. Our observations are in good agreement with the theoretical treatment of Yatsenko et al. (Opt. Comm. 282 (2009) 300) [1]

Pulsed frequency-shifted feedback laser for laser guide stars: intracavity preamplifier

International audienceIntensive use of Laser Guide Star (LGS) with the new generation of Extremely Large Telescopes and Hypertelescopes will requires the use of more efficient lasers to surmount the novel limitations and aberrations. The Pulsed Frequency Shifted Feedback (FSF) laser we have developed overcomes the saturation of sodium atoms and solves new problems. This work presents a highly efficient solution for operating pulsed FSF lasers. For the first time, an intra-cavity preamplifier achieves a gain of 104 and more than 40 μJ per pulse, with a near diffraction limited beam and without Amplified Spontaneous Emission. Endurance tests have shown that good performance is maintained over several hundred hours

Effects of laser beam propagation and saturation on the spatial shape of sodium laser guide stars

International audienceThe possibility to produce diffraction-limited images by large telescopes through Adaptive Optics is closely linked to the precision of measurement of the position of the guide star on the wavefront sensor. In the case of laser guide stars, many parameters can lead to a strong distortion on the shape of the LGS spot. Here we study the influence of both the saturation of the sodium layer excited by different types of lasers, the spatial quality of the laser mode at the ground and the influence of the atmospheric turbulence on the upward propagation of the laser beam. Both shape and intensity of the LGS spot are found to depend strongly on these three effects with important consequences on the precision on the wavefront analysis

High resolution cw laser beam preamplified in a multipass cavity pumped by a CuHBr (HyBrID) laser

International audienceThe amplification of a cw high resolution (1 MHz) single-mode dye laser in a single-stage, multipass preamplifier based on a free flowing dye jet as amplifying medium is reported. The device is pumped by a homemade CuHBr laser (HyBrID laser) (18 kHz repetition rate, 30 ns pulse duration at half-maximum and 80 ns at its base) and yields pulses of duration of 10 ns (at half-maximum). In the studied pump energy domain, the gain is a linear function of pump energy and the maximum value obtained so far with pump energy of 400 μJ is 25 μJ per pulse for an input beam power of 30 mW. The corresponding gain is of the order of 10 4. We assume that a higher gain can be reached using better quality elements. The output beam is a high quality TM 00 mode. The pulse shapes of the pump beam and the output beam are compared and a phenomenological model ("switched photon lifetime") is introduced that reproduces our observations with a good agreement

Intérêt de l’amendement et du paillage pour les plantations forestières en région méditerranéenne : le projet FP7 Sustaffor

En région méditerranéenne, il est nécessaire de faire l’entretien des jeunes plantations d’arbres pour faire face à la sécheresse et à la végétation concurrente. Ces interventions ont un grand impact économique, en plus d’avoir, lors de l’utilisation de plusieurs techniques (arrosage d’urgence, dégagement chimique ou mécanique), un effet négatif sur l’environnement. Dans le cadre du projet Sustaffor, de nouveaux produits innovants sont développés : un amendement de sol et trois prototypes de paillis, dont deux sont biodégradables (un nouveau biopolymère et une toile de jute) et un réutilisable (en caoutchouc recyclé). Ces produits sont étudiés dans le nord-est de l’Espagne dans quatre bioclimats méditerranéens représentatifs : semi-aride, méditerranéen continental, méditerranéen humide et étage montagnard. Durant les deux premières saisons de végétation, le nouvel amendement de sol a eu un effet très positif pour les sols légers ayant une faible capacité de rétention d’eau. Le paillage a été très efficace dans les conditions les plus productives et, dans une moindre mesure, en conditions limitantes. Les nouveaux produits permettent de réduire entre autres les entretiens nécessaires dans les plantations d’arbres, tout en présentant un avantage environnemental

Fourier transform: A tool to measure statistical level properties in very complex spectra

International audienceWe show that the Fourier transform of very complex spectra gives a sound measurement of long-range statistical properties of levels even in cases of badly resolved, poorly correlated spectra. Examples of nuclear energy levels, highly excited acetylene vibrational levels, and singlet-triplet anticrossing spectra in methylglyoxal are displayed