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DYNAMIQUE DE LA GENERATION D'HARMONIQUES DANS LES ATOMES ET LES MOLECULES

Abstract : High-order harmonic generation by focusing of femtosecond laser pulses in gases can produce attosecond pulses trains in the XUV domain. In this thesis, we present a technique for optimizing the generation efficiency. Then we show how one can study dynamics in molecules under strong field through the characterization of the radiation. In a first part, by spatial phase manipulation, we shape the laser profile near focus in order to enlarge the generation volume. We demonstrate the possibility to create a flat top profile, 2.5 times larger than the Gaussian one. We study the harmonic generation in rare gases, experimentally as well as numerically. Although we did not observe significant enhancement of the harmonic signal, simulations performed at higher laser energies predict a gain in efficiency. In a second part, we show that the harmonic spectrum and phase from a set of aligned linear molecules present structures due to the characteristics of the molecule. We put in evidence a phase jump linked to quantum interferences during the recombination step. We study this phase jump dependencies with several parameters, such as the molecule's orientation or the generation intensity. Electronic dynamics during the recombination of the electronic wavepacket can be inferred from these measurements. Moreover, they should be used as a test bench for new model of molecular dynamics under strong fields.
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https://tel.archives-ouvertes.fr/tel-00593728
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Submitted on : Tuesday, May 17, 2011 - 11:23:31 AM
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Willem Boutu. DYNAMIQUE DE LA GENERATION D'HARMONIQUES DANS LES ATOMES ET LES MOLECULES. Physique Atomique [physics.atom-ph]. Université Paris Sud - Paris XI, 2007. Français. ⟨tel-00593728⟩

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