Influence of modulation and shape of laser pump pulses on stimulated Brillouin scattering in self-focusing regime in silica

The propagation of powerful nanosecond optical pulses at the wavelength of 355 nm in thick silica windows usually gives rise to Kerr-induced multiple filamentation, which breaks the homogeneity of the energy distribution and can initiate surface or bulk damage. Part of the incident beam is furthermore back-reflected by stimulated Brillouin scattering (SBS), leading to the creation of a Stokes wave which is also source of damage at the front surface of the sample. To address this problem, the authors study the interaction of these two nonlinear effects from coupled envelope equations in full (3+1)-dimensional geometry. Emphasis is put on the influence of the incident pulse spatial profile and of phase or amplitude modulations applied to the pump wave.