Self-focusing of dark hollow Gaussian laser beam and its effect on second harmonic generation in collisionless plasma: Moment theory approach

This paper presents an investigation on the generation of second harmonics of dark hollow Gaussian (DHG) laser beam in plasma with collisionless nonlinearity. Due to uneven intensity distribution of beam the ponderomotive force moves plasma out of the high intensity region of the beam and thereby increases the dielectric constant of plasma which leads to the self-focusing of beam. The background density gradients excite the electron plasma wave (EPW) at pump frequency which on interaction with the incident laser beam produces its second harmonics. Moment theory approach has been used to derive the differential equation for the spot size of laser beam and by solving the nonlinear wave equation for second harmonics, the second harmonic yield (SHY) is obtained. In this work, the effect of different modes and intensity of pump beam on self-focusing as well as on SHY is analyzed.