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 IpIcr the gain increment tended to the static value. An anomalous scatter of the Raman amplifier gain was observed experimentally for Δνs≈Δνp≫Δνl (Δνs,Δνp, and Δνl 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.