TRANSIENT-RESPONSE OF PHOTOREFRACTIVE BISMUTH SILICON-OXIDE IN THE PULSED REGIME

The transient response of bismuth silicon oxide in the regime, pulsed exposure time << carrier recombination time, is modelled using the linearized band transport equations. The theory predicts a rapid build-up of photorefractive grating on a nanosecond time scale with response time inversely proportional to exposure. The build-up is followed by a decline in grating strength to a finite final value on a microsecond time scale. A permanent grating remains as time tends to infinity. The transient response is investigated experimentally by writing gratings in BSO with a frequency-doubled Q-switched Nd-YAG laser. The two main predictions of the theory - fast build-up followed by microsecond decline - are verified and the transverse photocurrent response confirms the carrier recombination time to be in the microsecond range. It is unexpected that the photorefractive grating continues to rise over a millisecond time scale indicating the presence of an unknown charge transfer mechanism. Another result is an induced absorption at the red (633 nm) wavelength.