Abstract
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 \AA{} at 295\ifmmode^\circ\else\textdegree\fi{}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 ${\ensuremath{\lambda}}^{\ensuremath{-}4}$ 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.
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