Picosecond photorefractive beam coupling in GaAs

We report the first observation to our knowledge of the photorefractive effect on picosecond time scales. Photorefractive beam coupling in GaAs with picosecond, 1.06-microm pulses is observed owing to charge separation between electrons and the ionized defect EL2(+) at low fluences and to separation between free electrons and holes created by two-photon interband absorption for high fluences. The accompanying processes of linear absorption, two-photon absorption, and transient energy transfer are also observed.