Interaction laser matière à haut flux et fort contraste temporel

Abstract : The continuous progress in laser installations has already lead to ultra-short pulses capable of achieving very high focalized intensities (I>1018 W/cm²). At these intensities, matter presents new non-linear behaviours, due to the fact that the electrons are accelerated to relativistic speeds. The experimental access to this interaction regime on solid targets has long been forbidden because of the presence, alongside the femtoseconde pulse, of a pedestal (mainly due to the amplified spontaneous emission (ASE) which occurs in the laser chain) intense enough to modify the state of the target.
In this thesis, we first characterized, both experimentally and theoretically, a device which allows an improvement of the temporal contrast of the pulse: the Plasma Mirror. It consists in adjusting the focusing of the pulse on a dielectric target, so that the pedestal is mainly transmitted, while the main pulse is reflected by the overcritical plasma that it forms at the surface. The implementation of such a device on the UHI 10 laser facility (CEA Saclay – 10 TW – 60 fs) then allowed us to study the interaction between ultra-intense, high contrast pulses with solid targets.
In a first part, we managed to generate and characterize dense plasmas resulting directly from the interaction between the main pulse and very thin foils (100 nm). This characterization was realized by using an XUV source obtained by high order harmonics generation in a rare gas jet.
In a second part, we studied experimentally the phenomenon of high order harmonics generation on solid targets, which is still badly understood, but could potentially lead to a new kind of energetic ultra-short XUV sources.
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Submitted on : Friday, March 24, 2006 - 10:38:36 PM
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Gilles Doumy. Interaction laser matière à haut flux et fort contraste temporel. Physique Atomique [physics.atom-ph]. Ecole Polytechnique X, 2006. Français. ⟨tel-00012038⟩

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