Dynamics of photoinduced lens formation in a photorefractive Bi_12TiO_20 crystal under an external dc electric field

Abstract

We report experimental results on the dynamics of formation of a photoinduced lens produced by a two-dimensional cw He–Ne Gaussian laser beam (633 nm) in a cubic Bi12TiO20 photorefractive crystal under an external dc electric field. The main features of the effect, namely, astigmatism of the dynamic lens formed, the pulse shape of the far-field response after switching on of the focused beam, inverse linear dependence of time of its growth on the beam intensity, and approximate constancy of its peak level, are explained in the framework of the analytical model for a one-dimensional Gaussian beam and numerical calculations for a two-dimensional one.