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Spectroscopie d'absorption ultra-rapide de rayonnement X pour l'étude de la matière en régime transitoire.

Abstract : In this work, we study the physics of dense matter, plasmas or solids, using x-ray absorption spectroscopy. Throug! h the use of sources produced by laser-matter interaction, we have measured the absorption spectra of aluminum and bromine plasmas, as well as those of vanadium dioxyde (VO2). The measurement of absorption coefficients allows us to probe the dense matter and to study its properties. The experiments are carried out following the same principle : they use the same experimental set-up, called pump-probe. When the matter is dense, the absorption properties of an atom are modified by the surrounding environment. In a plasma, it is mainly the bound- bound transitions which are altered : the shapes of those spectral rays are modified. In a solid, the position of the neighbouring atoms in relation to the absorbing atom modify the structure of absorption levels (bound-free transition). The study of this structure allows us to measure the parameters of the material, and provides information such as the state of the electronic band or the interatomic gaps. The experiments carried out at the LULI have allowed us to probe plasmas in the relatively unknown regime of the Warm Dense Matter. One of the key parameters is that the plasma is caracterised independently (FDI diagnostic). It allows for a better comparison of the measured absorption against a calculation made with the numerical model OPA-S. The experiments carried out at INRS have led to the realisation of an experimental system having the characteristics which allow the study of the dynamics of solids showing ultra-fast phase transition. For those experiments, we have used vanadium dioxyde as a model system allowing us to test the feasibility of the method.
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Submitted on : Thursday, July 22, 2010 - 11:30:34 AM
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  • HAL Id : pastel-00003732, version 1


Ludovic Lecherbourg. Spectroscopie d'absorption ultra-rapide de rayonnement X pour l'étude de la matière en régime transitoire.. Physique [physics]. Ecole Polytechnique X, 2007. Français. ⟨pastel-00003732⟩



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