The dynamics of coherently excited LO phonons is investigated in GaAs using an infrared time-resolved coherent anti-Stokes Raman scattering technique. The LO-phonon dephasing time is precisely measured as a function of crystal temperature. The results reveal that the relaxation is dominated by the intraband decay into a transverse-acoustic phonon and a LO phonon at the L critical point of the Brillouin zone. The frequently proposed decay route into two longitudinal-acoustic phonons is found to be incompatible with results from our temperature-dependent measurements.

• Received 16 January 1991

DOI:https://doi.org/10.1103/PhysRevB.43.12049