Backward Stimulated Raman Scattering

This paper describes in detail the initiation and growth of backward-traveling stimulated Raman-Stokes pulses. The radiation-transfer equations for the pulse development are derived, and a general analytic solution is given in the rate-equation approximation. Special solutions are given for a variety of pulse-initiation conditions. It is shown that in the presence of residual linear absorption, a steady-state Stokes pulse is expected, and its characteristics are described. Extensive experimental observations in C${\mathrm{S}}_2$ of the properties of the backward pulse and the forward emission are reported, including measurements of the pulse energy as a function of position in the cell, the pulse duration as measured by the intensity-autocorrelation technique, and the time sequence of the emission of the forward and backward pulses. Various experimental results indicate the dominant role played by self-focusing in the initiation of the backward pulse and the role of competing processes. The growth of the pulse energy is found to be consistent with the theory; a minimum pulse duration of 30 psec and a peak pulse power 20 times the instantaneous laser pump power are reported, indicating substantial depletion of the incident laser pump light.