Effect of domain structure fluctuations on the photorefractive response ofperiodically poled lithium niobate

We analyze theoretically the photorefractive response of periodically poled lithium niobate (PPLN) taking into account spatial fluctuations of its dom ain structure. It is shown that these fluctuations strongly affect the ampl itude of space-charge field in the limit of small photorefractive grating v ectors. The behavior of the nonlinear response in this limit is controlled by the root-mean-square of the spatial fluctuations of the domain structure . In the limit of large grating vectors, the nonlinear response is not sens itive to deviations from the ideal periodic geometry. The results obtained can be useful for the interpretation of photorefractive experiments and the formulation of requirements for the fabrication of photorefractive PPLN sa mples.