Stratégies de contrôle laser de la dynamique moléculaire PDF Download

Author: Catherine Lefebvre
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Languages : en
Pages : 159

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Book Description
This thesis studies the phenomenology of the molecular dynamics in intense laser field and, more precisely the basic mechanisms in the stabilization of a molecule with respect to the dissociation. The main line in these works concerns the dynamics of the Floquet resonances in intense laser field. Simple and generic strategies are proposed and applied to the one-dimension model of H2+ molecular ion for which time-dependent wavepacket calculations have been performed. Starting from the synchronization mechanism between the wavepacket movements and those of the potential energy curves, originally established in the infrared spectral domain where the quasi-static picture is used, we propose a scenario to extend its application to the ultraviolet-visible spectral domain where the multiphotonic picture is valid. In the Floquet representation, we observe a breathing of the dressed potential energy curves at the one-photon crossing following, not the carrier-wave oscillations, but those of the envelope of frequency lying in the infrared. We are particularly interested in the dependance of the molecular dynamics on the phase of the envelope and we use a recent reformulation of the Floquet theory to establish the origin of the dynamical role of the absolute phase. By a simple optimization of the optical parameters, we take advantage of the different basic mechanisms in the multiphotonic and quasi-static pictures in order to stabilize the molecule with respect to the dissociation via an adiabatic transfer of an initial vibrational state onto a resonance. Even more efficiently, this transfer is done onto a zero-width resonance. All these multiphotonic processes are then applied to the problem of the dissociative ionization of H2 for which we study the dynamics of H2+ molecular ion under a femtosecond near-infrared laser pulse, previously prepared from the neutral molecule by an extreme ultraviolet attosecond pulse. The study of the adiabatic or non-adiabatic character of the preparation of the ion and its subsequent evolution under the infrared pulse allows one to retrieve a signature of the dynamics of the Floquet resonances and an indirect image of the initial vibrational wavepacket. This type of molecular dynamics imaging brings a theoretical support for interpretation of experimental results concerning the photofragment kinetic energy spectra. Finally, using the same reformulation of the Floquet theory, we demonstrate the existence of a wavepackets interferometry, the wavepackets being individually prepared successively by each attosecond pulse in a train. This new scheme of an extreme ultraviolet attosecond pump pulse combined with an infrared femtosecond probe pulse gives in principle a strategy to characterize attosecond pulse trains.