Threshold and amplification of convective two-plasmon decay instability in a collisional laser plasma

The threshold and amplification of convective two-plasmon decay instability in a collisional laser plasma are investigated using the fluid theory. Taking into account the collisional damping of electron plasma waves, the expressions for the threshold intensity and the amplification coefficient are obtained. It is observed that the damping increases the threshold significantly for electron temperatures less than 1 keV, one threshold increasing by a factor of about 102 at a temperature of 100 eV. Analysis of the amplification coefficient shows that the plasmon spectrum greatly depends on the value of wavenumber component ky in a direction perpendicular to the direction of plasma inhomogeneity. Whereas for ky < ko, the laser wavenumber, the spectrum is narrower, for ky > ko, it is broader. The collisional damping significantly reduces the amplification coefficient as well as the plasmon spectrum. Results are discussed with reference to half-harmonic light emissions from laser plasmas. (Author)