Linear phase demodulation in photorefractive crystals with nonlocal response

On the basis of the vectorial theory of light diffraction in cubic photoref ractive crystals, we derive analytical expressions to describe the output i ntensities and polarization states of two coherent beams coupled via a dyna mic index grating and subjected at the input to a fast phase modulation. It is shown that the linear transformation of fast phase excursions into inte nsity modulation can be achieved in the case of a nonlocal ac response by m eans of proper polarization filtering. Theoretical results are supported by the data obtained in experiments with Bi12TiO20 crystals of different orie ntations. The polarization technique is used for the evaluation of the spac e-charge fields created in different crystals. (C) 2001 American Institute of Physics.