BUILDUP AND DARK DECAY OF TRANSIENT PHOTOREFRACTIVE GRATINGS IN REDUCED KNBO3

Build-up and decay of transient photorefractive gratings written with 200 ns pulses (intensity up to 20 kW/cm2) in reduced KNbO3 were studied. Grating build-up times of about 1 μs were measured. Saturation effects and fast transients preceding a millisecond dark decay were observed. From an accurate measurement of the temperature dependence of the dark decay we could identify a component with an activation energy of 0.3 eV that may be attributed to a shallow trap level. The measurements were compared with the results of computer simulations based on the band transport model. The observed phenomena can be described by a single carrier model assuming that an additional shallow electron trapping level is present below the conduction band. © 1990.