Brillouin shifted third harmonic generation of a laser in a plasma

摘要

The process of Brillouin shifted resonant third harmonic generation of an intense laser of finite spot size in a plasma is investigated. The laser of frequency ω_0 and wave number k_0 excites an ion acoustic wave of frequency ω≈kc_s and wave number k≈2k_0, where c_s is the ion acoustic speed, in the primary stimulated Brillouin scattering process. The laser also exerts a second harmonic ponderomotive force on electrons. This imparts them an oscillatory velocity v_(2ω_0), 2k_0. This velocity beats with the electron density perturbation associated with the ion acoustic wave to produce a density perturbation at Brillouin shifted second harmonic. This perturbation couples with the oscillatory velocity v_(ω_0), k_0 due to the laser to produce Brillouin shifted third harmonic current density and the radiation field. The phase matching is satisfied when plasma density is two third critical.