Stimulated Brillouin Scattering of Elliptical q-Gaussian Laser Beams in Plasmas with Axial Density Ramp: Effect of Self-Focusing

Theoretical investigation on stimulated Brillouin scattering of intense q-Gaussian laser beams interacting with axially nonuniform plasmas has been presented. A ramp-shaped density profile has modelled the axial inhomogeneity of the plasma and the optical nonlinearity of the plasma has been considered to be originating owing to the dependence of the relativistic mass of the plasma electrons on laser intensity. An intense laser beam with frequency ω 0 propagating through plasma gets coupled with a preexisting ion acoustic wave (IAW) at frequency ω ia and produces a backscattered wave at frequency ω s = ω 0 – ω ia . Using variational theory semi-analytical solution of the set of coupled wave equations for the pump, an IAW and a scattered wave have been obtained under W.K.B. approximation. It has been noted that the power of the scattered wave is significantly affected by the self-focusing effect of the pump beam.