Two‐dimensional studies of stimulated Brillouin scattering, filamentation, and self‐focusing instabilities of laser light in plasmas

The parametric interaction of an intense laser beam with ion plasma modes in a two‐dimensional Cartesian geometry has been studied for the first time by avoiding the paraxial optics approximation. This model allows investigation of the competition between forward, sideward, and backward stimulated Brillouin scattering (SBS) along with filamentation and self‐focusing instabilities. It is shown that the SBS saturation level, the angular distribution of transmitted and scattered light, and their temporal dependence are governed mainly by two control parameters: the backward SBS gain coefficient G, and the ratio αsf of the incident beam power to its critical value for the onset of self‐focusing. In the case of large values of G≳15, backward SBS dominates and prevents both self‐focusing and forward SBS. For smaller values of G, the interaction exhibits a complex oscillatory behavior, which corresponds to the competition between backward and forward SBS for αsf≲1, and involves also self‐focusing for higher beam...