6533b832fe1ef96bd129aaf0

RESEARCH PRODUCT

On the study of the laser filamentation process in rare gases under the strong field model : impacts of third harmonic generation and of the vicinity of resonances in the ultraviolet

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Filamentation originates from the dynamic balance between linear and nonlinear effects, allowing the laser beam autostabilization over distances significantly greater than those predicted by linear optics laws. The aim of this thesis is to describe this phenomenon on rare gases under the strong field model, contrary to the commonly used perturbation model based on the weak field approximation. The influence of harmonics, so far neglected, is then revisited both at the microscopic level and at a propagation scale. It is shown, experimentally and with the support of numerical simulations, that a weak proportion of third harmonic is sufficient to strongly impact the filamentation dynamics, especially through the ionization process. Also, the vicinity of a resonance can lead to strong modifications of the self-guiding mechanism: when a fundamental field centered at 400nm and its third harmonic interact together with krypton, it is shown that the cross-phase modulation process is enhanced and can participate to the beam defocusing. Another situation - at 300nm in krypton - leads to resonantly enhanced filamentation, i.e. to longer filaments compared to the non-resonant case.