Beat wave excitation of electron plasma wave by cross-focusing of intense cosh-Gaussian laser beams in collisionless plasma with upward density ramp

Abstract

This paper presents theoretical investigation of the effect of cross-focusing of two coaxial cosh-Gaussian (ChG) laser beams on beat wave excitation of electron plasma wave (EPW) in an under dense plasma with upward density ramp. The plasma wave is generated on account of beating of two coaxial laser beams of frequencies ω1 and ω2. The mechanism for laser induced nonlinearity is assumed to be a ponderomotive force. Following moment theory approach in Wentzel–Kramers–Brillouin (W.K.B) approximation nonlinearly coupled differential equations governing the evolution of spot size of the laser beams with distance of propagation have been derived. The ponderomotive nonlinearity depends not only on the intensity of first laser beam but also on that of second beam. Therefore, the behavior of first laser beam affects that of second laser beam and hence cross focusing of two laser beams takes place. By changing the decentred parameter, the peak intensity of the laser beam can be shifted in the transverse direction and a noticeable change is observed on the cross-focusing of the two laser beams as well as on the power of generated plasma wave. The results are presented in the form of graphs for typical set of laser-plasma parameters.