On the effect of long-wavelength electron plasma waves on large-angle stimulated Raman scattering of short laser pulse in plasmas

Spectral features of a large-angle stimulated Raman scattering (LA SRS) of a short electromagnetic pulse in an underdense plasma, which are caused by the presence in a plasma of a given linear long-wavelength electron plasma wave (LW EPW), are investigated. It is shown that the LW EPW, whose phase velocity coincides with a group velocity of a pulse and a density perturbation normalized to a background electron density /spl delta/n/sub LW//n/sub 0/ exceeds the ratio of the electron plasma frequency to the laser frequency /spl omega//sub pe///spl omega//sub 0/ suppresses the well-known Stokes branch of the weakly coupled LA SRS. Under the same condition, the anti-Stokes band appears in the spectrum of the scattered radiation. Variation of a scattering angle and an electron temperature do not significantly modify qualitative features of the effect. In the case of strongly coupled LA SRS, the maximum of the increment is decreased by nearly one-half for /spl delta/n/sub LW//n/sub 0//spl sim/(a/sub 0//spl omega//sub pe///spl omega//sub 0/)/sup 2/3//spl Gt//spl omega//sub pe///spl omega//sub 0/, where a/sub 0/ is an amplitude of an electron quiver velocity in the laser field normalized to a speed of light c, and it decreases further with an increase in plasma density perturbation in LW EPW.