PHASE MODULATION IN 2-WAVE MIXING FOR DYNAMICALLY RECORDED GRATINGS IN PHOTOREFRACTIVE MATERIALS

We derive an analytical expression describing the effect of phase modu lation in two-wave mixing for dynamically recorded phase-shifted holog rams in photorefractive materials. The temporal harmonic terms that ar ise from phase modulation are explicitly formulated for small modulati on (as used in our experiments), allowing for pump depletion and an ar bitrary value of the phase shift. The theory is experimentally verifie d for the particular case of an unshifted hologram in a photovoltaic L iNbO3 crystal and for the general case of an arbitrarily shifted holog ram in a Bi12TiO20 crystal subject to an externally applied electric f ield, always for the 514.5-nm-wavelength laser light. In both cases th e present analytical formulation permits material parameters to be com puted that are self-consistent and in agreement with data in the liter ature. (C) 1997 Optical Society of America.