Filamentation d'impulsions laser ultra-courtes dans l'air et dans l'eau : étude des processus de transfert d'énergie

Abstract : With the development of ultrashort lasers, pulses with peak power in the gigawatt level are easily obtained. In this intensity range, the propagation is no longer linear. Due to the Kerr effect, the beam self-focuses and tends to collapse until the intensity is high enough to ionize the medium, an effect that defocuses the beam. A dynamic competition takes place between Kerr effect, ionization and diffraction, resulting in a spectacular reshaping of the beam in an intense core propagating over many Rayleigh lengths. During this phenomenon, called laser filamentation, a thin and weakly ionized plasma channel is left in the trail of the pulse. This propagation mode strongly affects the pulse and the medium where it happens. Through several collaborations, I focus this work on experimental studies of the impact of the filamentary propagation in gases and liquids. I thus mapped the spatio-temporal distortions of the pulse during its propagation in water and identified their signatures in the spatial, spectral and energetic domain. I then characterized the energy losses in water and the shock wave generated by the plasma relaxation in different power ranges and focalisation geometries, for the generation of acoustic waves by femtosecond laser pulses. On the other hand, I studied the plasma generated at the intersection of two crossing filaments in molecular and atomic gases. I demonstrated that its spatial properties and transient behaviour can spatially and temporally filter a laser pulse, and could potentially offer a new alternative to generate femtosecond laser pulses with a high contrast and good quality beam profile. Finally I characterized the compression of high energy femtosecond pulses with a planar hollow waveguide and demonstrated that the time compressed pulses can be used to generate high order harmonics, and in general for high field physics.
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Submitted on : Wednesday, January 7, 2015 - 3:30:20 PM
Last modification on : Wednesday, July 3, 2019 - 10:48:02 AM
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Amélie Jarnac. Filamentation d'impulsions laser ultra-courtes dans l'air et dans l'eau : étude des processus de transfert d'énergie. Optique [physics.optics]. Ecole Polytechnique, 2014. Français. ⟨tel-01101002⟩

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