Investigations of photorefractive effects with pico and nanosecond pulses

Abstract

We give a short overview over pulsed photorefractive experiments and present measurements performed in orthorhombic KNbO₃ with nanosecond and picosecond pulses that allowed the investigation of some material parameters. We discuss the dark decay of the grating after pulsed illumination and show that from the temperature dependence of the decay the existence of a shallow trap level with a thermal excitation energy of approximately 0.3 eV can be inferred. From the dynamics of the grating build-up on a microsecond time scale we deduce a recombination time of the order of microseconds. After illumination with 70 ps pulses the photorefractive grating builds-up in reduced KNbO₃ in about 5 nanoseconds. This build-up time is typical for reduced KNbO₃ and does not change by more than 20%if the grating-spacing is changed by a factor of ten or the temperature is increased to 165°C.