Spectra of backward stimulated Raman scattering of short relativistically strong laser pulses in an underdense plasma

A theory of the backward stimulated Raman scattering of short relativistically strong laser pulses in an underdense plasma is developed. Analytical study and particle-in-cell simulations show that, if the pulse excites a nonlinear wake plasma wave, a strong up-or downshift of the backscattered radiation frequency can occur. It is shown that the structure of the backscatter spectrum depends strongly on the shape of the pulse.