PHOTOREFRACTIVE GRATING FORMATIONS AT LARGE MODULATION WITH ALTERNATING ELECTRIC-FIELDS

A finite-difference technique was used to model photorefractive grating formations in sillenite crystals under nonstationary recording conditions of applied ac electric fields. These numerical results predict the magnitude, spatial distribution, and temporal evolution of the space-charge field at large modulations. The modulation-index-dependence of the magnitude of the fundamental component of the space-charge field was well described by the correction function f(m) = [1 - exp(-am)]exp(m). The value of the correction parameter a was correlated with crystal parameters and external conditions. These results were generalized to other crystal parameters and expressed as analytical functions that approximate the numerical solutions.