<title>Theory of SRS of short laser pulse in underdense plasma</title>

Abstract

region, Russian Federation AB STRACT Both analytical and numerical analysis of weakly coupled backward stimulated Raman scattering (BSRS) of a modulated laser pulse in an underdense plasma is made. In that regime the spectrum of a backscattered field contains only the usual Stokes lines from respective spectral components of a laser pulse, each narrow compared to w1 . Additionally, the intensity of radiation, backscattered from a given spectral component of a laser pulse, drammatically lowers in appearing in the pulse spectrum of another component, red-shifted by 2 Wpe with respect to the former. It is proved that a long-wavelength plasma wave with a relativistic phase velocity, propagating in plasma, affects the mode structure of weakly coupled BSRS. It is shown via direct numerical modeling that the strong pulse modulation visibly modifies the spectrum of strongly coupled BSRS. The linear theory clarifies some details of numerically modelled evolution of BSRS spectra due to nonlinear pulse evolution. 0-8194-2 155-3/96/$6.00 SPIE Vol. 2770 /53 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/15/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx 20, and (koL)2 = 4000, b) fi = 17.5 at e = 1, (w8/c)L = 10, and (koL)2 = 17500. The spectral density of BSRS which corresponds to the same parameters but = -'BG are plotted on Figs 3 to compare them with Figs 2. Difference between 2a and 3a is related to the resonant stabilizing of the "blue" wave scatter, 2b SPIE Vol. 2770 /59 Downloaded From: http://proceedings.spiedigitallibrary.org/ on 06/15/2016 Terms of Use: http://spiedigitallibrary.org/ss/TermsOfUse.aspx