Influence of the spectral width and statistics of a Stokes signal on the efficiency of stimulated Raman scattering of nonmonochromatic pump radiation

A theoretical and experimental investigation was made of the amplification of a Stokes signal in a multimode pump field when the ratio of the spectral widths of the interacting fields was varied. In the pump intensity range I_p < I_cr (I_cr was a critical intensity) the gain increment was considerably less than the static value and it was governed entirely by the spectral distributions of the pump and Stokes signal. In the range I_p > I_cr the gain increment tended to the static value. An anomalous scatter of the Raman amplifier gain was observed experimentally for Δν_s ≈ Δν_p≫Δν_l (Δν_s, Δν_p, and Δν_l were the line widths of the Stokes signal, pump, and spontaneous stimulated Raman scattering). A theory developed for the purpose indicated that the scatter was observed because the phase relationships between the interacting waves at the input into the medium varied from one measurement to another.