Time-Resolved Investigations of Stimulated Brillouin Scattering in Transparent and Absorbing Media: Determination of Phonon Lifetimes

Stimulated Brillouin scattering was studied both theoretically and experimentally. The evolution in time of the scattering process, its dependence on frequency, and the influence of optical absorption were analyzed. For quantitative investigations, the individual shapes of the laser and signal pulses were taken into account. Strong transient effects predicted by theory were confirmed experimentally. The amplification of Brillouin light was measured in a generator-amplifier system using single-mode giant laser pulses. Several liquids, glasses, and quartz were investigated. The experimental results allow the determination of phonon lifetimes $\ensuremath{\tau}$ and of elasto-optic constants. In our amplifier system, accurate values of $\ensuremath{\tau}$ are obtained for $\ensuremath{\tau}<3$ nsec, i.e., for liquids and some solids. The limitation of the method is discussed. In absorbing media, stimulated thermal Brillouin scattering was observed in quantitative agreement with theory.