A new model of Raman spectra in laser produced plasma

Experimental observations of Raman scattering in laser produced plasma can be explained by ordinary incoherent Thompson scattering, with a greatly enhanced plasma line. Transient local reversed-slope velocity distributions in the underdense region can be produced by pulses of hot electrons arising from the two-plasmon or absolute stimulated Raman instabilities (SRS-A) occurring near the quater critical surface. A simple model yields the observed spectral gaps near the incident frequency (LC OMEGA) 0 and near (LCOMEGA)0/2. It also explains the correlation of onset of this scattering with onset of the SRS-A, its transient localization in frequency and time, and the weak azimuthal angular variation. The existence of an upscattered frequency band is also predicted and been verified by experiment.