<title>Mechanism of external electric field influence on the process of hologram building-up in photorefractive crystals</title>

Abstract

The external electric field influence on the stationary state, that existed in the photorefractive crystal under inhomogeneous illumination before the field appeared, is analyzed. In this case, the additional charge grating is built-up and its amplitude is found to be proportional to the charge amplitude of initial grating and the field value. The building-up time of this grating does not depend on the field value and it is equal to the Maxwell relaxation time. However, the charge growth velocity is proportional to the electric field value. Consequently, the time interval which is necessary to obtain the set charge value providing sufficient diffractional efficiency decreases whereas the electric field increases. The expression connecting this interval with a corresponding value of the field is found. The dependence of a free charge carrier concentration on the light intensity for the two possible crystal types, in one of which the photorefractive centers are traps and in the other they are donors, is analysed too. The conditions are elucidated where this dependence becomes sublinear for relatively not high levels oflight intensity.