Picosecond photorefractive and free-carrier transient energy transfer in GaAs at 1 mu m

The strength, formation, and decay of photorefractive and free-carrier gratings written in GaAs by 43-ps pulses at a wavelength of 1 mu m are investigated using picosecond-time-resolved two-beam coupling, transient grating, and degenerate-four-wave-mixing techniques. Photorefractive weak-beam gains of a few percent are measured at fluences of a few pJ/ mu m/sup 2/ (0.1 mJ/cm/sup 2/), and gain from transient energy transfer is observed at fluences larger than approximately 10 mJ/cm/sup 2/ in the beam-coupling experiments. The roles of saturation and two-photon absorption in determining the final electron, hole, and ionized-donor populations and the roles of drift and diffusion in determining the quasi-steady-state photorefractive and free-carrier index modulations are discussed.< >