BRAGG-SHIFT OF HOLOGRAPHIC GRATINGS IN PHOTOREFRACTIVE FE-LINBO(3) CRYSTALS

In order to obtain the maximum diffraction efficiency, holograms recor ded in a photorefractive crystal must be replayed by a readout beam in cident at the correct angle. The optimum angle may be shifted away fro m the angle used for recording by a ''Bragg-shift'', caused (under cer tain conditions) by phase coupling between the two writing beams durin g recording. Although this Bragg-shift is small, a large diffraction e fficiency enhancement is obtained when the grating is read out at the optimum angle. In this paper detailed numerical calculations of the Br agg-shift are presented, based on an earlier theory, and a good agreem ent between theory and experiment is reported.