Dynamics of the emission and amplification of light in stimulated Raman scattering

A theoretical and experimental investigation was made of the dynamics of a Raman laser emitting two Stokes components. It is shown that when the second Stokes component appears, the quantum efficiency of the first component reaches 50% and then falls with rising pumping intensity. The results are given of a study of transient processes and saturation in two types of Raman amplifier: 1) parallel amplifier in which the pump and signal waves travel in the same direction; 2) opposed amplifier in which the pump and signal waves are antiparallel. It is established that for the same pumping intensity the saturation in the parallel amplifier occurs at a lower input signal than in the opposed amplifier. The divergence of the Stokes signal at the input and output of the amplifier is close to the diffraction limit. In the parallel variant the quantum efficiency under strong saturation conditions is close to 100% and the shape of the output pulses is governed by the shape of the pump pulses. In the opposed variant the leading edge of the Stokes pulses becomes shorter under saturation conditions.