MATHEMATICAL MODELING ON STIMULATED RAMAN SCATTERING INSTABILITY OF LASER BEAM PROPAGATINGTHROUGH COLLISIONAL PLASMA IN A SELF-FOCUSED FILAMENT INCLUDINGTHE EFFECT OFTHERMAL CONDUCTION

Abstract

Collisional plasma causes self-focusing of laser beam via Ohmic heating and density distribution.
 The self focusing, leads to enhancement of wave intensity, elevation of electron temperature and reduction of
 local electron density, leading to diminished attenuation rate. Thermal conduction plays an important role
 in temperature equilibrium when the electron mean free path m
 is greater than the beam radius ( m
 ro
 ).
 For 1
 m, (> ro
 , thermal conduction suppresses any non-uniformities in electron temperature, and nonlinearity
 is dominated by ponderomotive force. Stimulated Raman scattering instability is treated for laser beam
 propagating through collisional plasma in a self-focused filament where nonlinear refraction due to the
 redistribution of the electron density caused by nonuniform Ohmic heating of electron is balanced by diffraction
 divergence. Thermal conduction could play a dominant role in determining the energy dissipation of electrons.
 Inside a filament, the laser undergoes stimulated Raman backscattering (B-SRS). The filament supports
 radially localized Langmuir waves. Since the temperature inside a filament is higher and density lower than
 those outside, the collisional damping rates of the decay waves are lowered hence the threshold power for B
SRS is reduced.