Couplage entre auto-focalisation et diffusion Brillouin stimulée pour une impulsion laser nanoseconde dans la silice

Abstract : As part of the studies on laser damage linked to the Megajoule project, we analyze the coupling between the Kerr induce self-focusing and the stimulated Brillouin backscattering pour nanosecond optical pulses propagating in silica samples. The influence of the incident power, phase or amplitude modulations as well as the spatial profile of the pulse of the filamentation dynamic is discussed. We show that an appropriate amplitude modulation dividing the incident pulse in pulse trains of picosecond durations suppresses the Brillouin effect for any incident power but noticeably reduces the available average laser power. On the contrary, phase modulated pulses with a comparable spectral width can undergo multiple filamentation and self-focusing at a shorter distance, caused by modulational instabilities. We demonstrate however the existence of a critical spectral bandwidth from which the backscattering can be radically inhibited by a phase modulation, even for high powers. This conclusion remains valid for spatially broader squared pulses, which self-focus earlier and break into multiple filaments at shorter distances. The inclusion of plasma generation to limit the growth of pump and Stokes waves is finally addressed.
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Sarah Mauger. Couplage entre auto-focalisation et diffusion Brillouin stimulée pour une impulsion laser nanoseconde dans la silice. Autre [cond-mat.other]. Université Paris Sud - Paris XI, 2011. Français. ⟨NNT : 2011PA112146⟩. ⟨tel-00638962⟩

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