SPACE-CHARGE WAVES IN PHOTOREFRACTIVE FERROELECTRICS

The conditions for the existence and the main characteristics of weakl y damped space-charge waves are investigated for photorefractive ferro electrics. These conditions are opposite those derived previously for sillenites and may be fulfilled in such crystals as LiNbO3, BaTiO3, an d SrBaNb2O6. The waves exist for sufficiently large values of the appl ied or photovoltaic field and have a linear dispersion law. The resona nce excitation of space-charge waves by a moving Light pattern is inve stigated. Possible manifestations of the instability of the photorefra ctive grating against parametric excitation of eigenmodes are consider ed.