SPEED LIMIT OF THE PHOTOREFRACTIVE EFFECT IN KNBO3

We present time resolved measurements of photorefractive grating build-up in reduced and unreduced KNbO3 crystals. After writing with 70 ps laser pulses at 532 nm the photorefractive diffraction efficiency reaches a stationary value in about 5 ns. The dynamics of grating build-up for different configurations exploiting isotropic and anisotropic Bragg diffraction and for different crystal temperatures is reported. We show that the build-up time is remarkably constant over many different experimental conditions.