Numerical simulation of filamentation and its interplay with SBS in underdense plasmas

We present results of a new code which models the interaction of intense electromagnetic beams with the low-frequency dynamics of the plasma fluid in two or three spatial dimensions. The light propagation is treated without the restriction of the paraxial optics approximation. The numerical scheme is based on spatial discretisation in the direction along the axis of the incident laser light whereas the transversal directions are treated spectrally. The specific cases discussed here refer to conditions found in recent experiments where filamentation was diagnosed [1]. In this study we first focus on effects originating from filamentation and/or forward stimulated Brillouin scattering (SBS), which can hardly be distinguished in the nonlinear case. We discuss then the impact of side- and backward SBS on these effects, observing the onset of an absolute filamentation instability predicted by Luther et al. [2].