Abstract

Highly excited ("hot") conduction band electrons in GaAs lose their energy primarily by the emission of zone center LO phonons¹. The quantitative study of this emission process requires the ability to measure the vibrational spectrum of GaAs on a sub-picosecond time scale. We have combined a sync-pumped dye laser with a filtered fiber optic pulse compressor to obtain spectrally clean 600 femtosecond pulses for wavelengths between 580 nm and 610 nm. A pump pulse generates excited carriers and a weaker, delayed probe pulse measures the Raman scattering from the phonons created by these carriers. Because the average probe beam power is of the order of 1 milliwatt and has a spectral full width at half maximum of about 30 cm^-1, the weak Raman scattered spectrum is detected by a cooled, microchannel plate photomultiplier with a position sensitive resistive anode. Changes of less than 10% from the equilibrium room temperature phonon population can be observed using this system. Spectral shifts of the order of 10 cm^-1 can be resolved.

© 1985 Optical Society of America