Detection of small phase modulation using two-wave mixing in photorefractive crystals

Two-wave mixing of phase-modulated beams in photorefractive crystals under a de electric field is studied bath theoretically and experimentally. Based on the vectorial theory of light diffraction in crystals of cubic symmetry , we derived an analytical expression that describes the phase demodulation in crystals with an arbitrarily oriented electric field. The phase-demodul ation technique was used for estimation of the space-charge field created i n photorefractive crystals. It is shown that the space-charge-field grating created in Gap and Bi12TiO20 crystals is much smaller than that predicted from the one-level band-transport model of the photorefractive effect.