Simulated Raman scattering instability of laser beam in a plasma channel

Abstract

A high power laser beam propagating through collisional plasma creates a low density channel through which it propagates self-guided. This equilibrium, however, is unstable to stimulated Raman back scattering above a threshold power. The self focusing, leads to enhancement of wave intensity, elevation of electron temperature and reduction of local electron density, leading to diminished attenuation rate. Stimulated Raman scattering instability is treated for laser beam propagating through collisional plasma with thermal conduction in a self-focused filament. Thermal conduction could play a dominant role in determining the energy dissipation of electrons. Inside a filament, the laser undergoes stimulated Raman backscattering. Since the temperature inside a filament is higher and density lower than those outside, the collisional damping rates of the decay waves are lowered and hence the threshold power for B-SRS is reduced. It remains an important process in laser produced plasma. It is also a limiting process in a plasma- loaded free electron laser.