Resonant Brillouin Scattering in GaAs

The dispersion of the Brillouin-scattering cross section of fast-TA phonons in GaAs was measured in detail in the range 8850 to 11 500 Å at 295°K. Acoustoelectrically amplified domains supplied very intense acoustic flux in the range 0.2-1.0 GHz; this permitted a detailed study of the dispersion with a monochromator and a continuous light source. Close to the intrinsic absorption edge, we see a resonant contribution to the scattering cross section. Further from the edge, a deep minimum indicates that the contributions to the elasto-optic coefficient $P_{44}$ from resonant and nonresonant terms have opposite signs. At still longer wave-lengths, the dominant trend is determined by the expected ${\lambda }^{-4\mathrm{}}$ dependence of the scattering cross section. The effect of increasing phonon intensity on the dispersion curve was studied and correlated with an associated broadening of the intrinsic absorption edge.