Photorefractive effects induced by picosecond light pulses in reduced KNbO_3

We discuss the writing of a photorefractive grating with pulses much shorter than the diffusion time of photoexcited charge carriers and compare the results with experiments performed in reduced KNbO3 crystals. From the grating-spacing dependence of the observed buildup time and diffraction efficiency we show that the lifetime of the photoexcited electrons is approximately 4 ns and that the mobility of these electrons before trapping is 0.4 ± 0.2 cm2/(V s).