Low-Frequency Noise and Photoinduced Scattering in Photorefractive Crystals

Photoinduced scattering (PS) is inherent in a varying degree in any photorefractive crystal. The origin of the PS is quite clear: this is an amplification of the weak seed scattering. A number of papers, for example [1-3], deal with a description of the effect. The pump and scattered waves supposed usually to have the same frequency. In the framework of that approach, a steady-state PS may only be caused by the nonlocal photorefractive response (i.e. by shifted gratings). However, in many cases experiments show the steady-state PS to be abnormaly large and this can not be accounted for by the nonlocal response. LiNbO3:Pe crystals, where the local response (i.e. unshifted gratings) exceed in value the nonlocal one by 101-102 times, can be pointed out as an example.