Investigation of Nonequilibrium Phonons in GaAs

The propagation of acoustic phonons in GaAs generated by laser radiation of a clean as well as Au coated surface are experimentally investigated in dependence on the crystallographic orientation. The angular dependence of the T1 phonon spectrum is confirmed by comparison with the calculated focussing factor. Besides the ballistic motion of modes of L, T1, and T2 polarization a further peak is observed in the time of flight spectra, which is interpreted by repeated conversion and decay processes of high-frequency phonons leading to T2 modes with a frequency low enough for ballistic motion. [Russian Text Ignored]