Influence of shallow traps on the enhancement of the photorefractive grating amplitude by a high-frequency alternating electric field: a probabilistic analysis

Abstract : We calculate the photorefractive grating amplitude in the presence of a high-frequency applied electric field in terms of the mean-square drift length of the charge carriers. We describe how a shallow-trap level and the related long effective deep-trap recombination time are detrimental to the enhancement produced by a squarewave field. We give expressions for the shallow-trap-induced reduction in the steady-state photorefractive gain as well as for its frequency dependence. The photorefractive gain reaches the same value obtained in the one-level model at low frequencies but falls almost exponentially to a shallow trap-limited value for higher frequencies. We compare the predictions of our model with other existing models and with experimental data.