Gain and line width in stimulated Brillouin scattering in gases

The thresholds of stimulated Brillouin scattering and the velocities of hypersound were determined experimentally for CH₄, N₂, Xe, and SF₆. The instantaneous powers of a laser beam at the entry to a gas-filled cuvette and of the beam transmitted by the gap were recorded by two photocells. The signals from these photocells were applied to the horizontal and vertical deflection systems of a cathode-ray tube. Oscillograms obtained in this way were used to determine the threshold of stimulated Brillouin scattering. The threshold powers for different gases were compared with the corresponding value for methane at a pressure of 105 atm, for which the gain was calculated theoretically. The velocity of hypersound was deduced from the frequency shift between the spectra of the exciting and scattered radiation. The results of the measurements were used to calculate the linewidths and gains.