Phase modulation in two-wave mixing for dynamically recorded gratings in photorefractive materials

We derive an analytical expression describing the effect of phase modulation in two-wave mixing for dynamically recorded phase-shifted holograms in photorefractive materials. The temporal harmonic terms that arise from phase modulation are explicitly formulated for small modulation (as used in our experiments), allowing for pump depletion and an arbitrary value of the phase shift. The theory is experimentally verified for the particular case of an unshifted hologram in a photovoltaic LiNbO3 crystal and for the general case of an arbitrarily shifted hologram in a Bi12TiO20 crystal subject to an externally applied electric field, always for the 514.5-nm-wavelength laser light. In both cases the present analytical formulation permits material parameters to be computed that are self-consistent and in agreement with data in the literature. (C) 1997 Optical Society of America.