Raman Scattering from Nonequilibrium LO Phonons with Picosecond Resolution

A novel technique is described for time-resolved Raman scattering for studying the dynamics of nonequilibrium excitations on a picosecond time scale. The generation and the decay of nonthermal LO phonons in GaAs is measured, and ${\tau }^{\prime }=7\mathrm{}\pm 1$ ps is obtained for the relaxation time of the phonon population at 77 K.