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Theses

Étude et réalisation de la pré-amplification d'impulsions à dérive de fréquence par amplification paramétrique optique.

Abstract : The research area of this thesis is the optical parametric chirped pulse amplification (OPCPA). It is a promising technique for improving the quality of ultra short and intense laser pulses, which aims at replacing traditional laser preamplifiers based on Titanium Sapphire. It has many advantages, among which the absence of spectral shortening. For a few years, the OPCPA technique has been used in many French and foreign laboratories, in high power laser systems, or for the generation of ultra-short pulses. We wished to study the experimental limits of this technique in order to use it as an injector for a high intensity laser system. OPCPA is a second-order nonlinear optical effect which combines parametric amplification and chirped pulse amplification technologies. An intense optical source (called the "pump") and a weak signal source (called the "seed") interact in a nonlinear crystal, allowing the amplification of the signal and the generation of a new wave known as the "idler". Two configurations allowing a broadband phase matching corresponding to very short pulses will be presented. The first configuration is a non-degenerate, non-collinear, parametric interaction. The seed and the pump beams are produced by two independent laser sources and their temporal synchronization is external. The second configuration is quasi-degenerate and quasi-collinear. Both beams come from the same laser source and are thus automatically synchronised. The second type of interaction proved to be the most promising for the studies we wished to carry out. Therefore, its development was pursued further, by setting up a hybrid type of amplification in which a parametric amplifier is combined with a traditional Titanium Sapphire multipass amplifier. The amplified signal is then temporally re-compressed by a group of four prisms associated with an acousto-optic filter with a programmable dispersion. The spatial profile and wavefront of the seed are well preserved during amplification. After amplification, an energy of 300 µJ and a gain higher than 105 were obtained, without reduction of the spectral bandwidth. The duration of the pulses after temporal recompression is 35 femtoseconds. Further improvements will be made to this experimental system in the near future, using the results of this thesis and its description of the technological bottlenecks. The results obtained are promising and prove the interest of such a technology for its use in the amplification of ultra-short laser pulses.
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Amandine Renault. Étude et réalisation de la pré-amplification d'impulsions à dérive de fréquence par amplification paramétrique optique.. Optique [physics.optics]. Ecole Polytechnique X; ENSTA ParisTech, 2006. Français. ⟨pastel-00603579⟩

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