Stimulated Raman scattering of self-focused elliptical q-Gaussian laser beam in plasma with axial density ramp: effect of ponderomotive force

摘要

Abstract The phenomenon of stimulated Raman scattering (SRS) of elliptical q-Gaussian laser beams interacting nonlinearly with underdense plasmas has been investigated theoretically. When an intense laser beam with frequency ω0documentclass12pt{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}$$omega _0$$end{document} propagates through plasma, due to the nonuniform irradiance over its cross-section d.c component of ponderomotive force becomes active. Due to this ponderomotive nonlinearity of plasma, the laser beam gets coupled with a preexisting electron plasma wave (EPW) at frequency ωepdocumentclass12pt{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}$$omega _{ep}$$end{document}. The nonlinear interaction of pump beam with EPW produces a back scattered wave at frequency ωs=ω0-ωepdocumentclass12pt{minimal} usepackage{amsmath} usepackage{wasysym} usepackage{amsfonts} usepackage{amssymb} usepackage{amsbsy} usepackage{mathrsfs} usepackage{upgreek} setlength{oddsidemargin}{-69pt} begin{document}$$omega _s=omega _0-omega _{ep}$$end{document}. Using variational theory semi-analytical solution of the set of coupled nonlinear wave equations for the three waves (pump, EPW and scattered) has been obtained under W.K.B approximation technique. It has been observed that power of the scattered wave is significantly affected by the self-focusing effect of pump beam.