Dispersion law of photorefractive waves in sillenites

Abstract

We investigate the dispersion law (relationship between Omega(k) and K) of photorefractive waves using a new experimental method based on the excitation of photorefractive waves by a spatially oscillating interference pattern and on the detection of the first non-Bragg diffraction order. The existence of a sharp resonancelike dependence of the output signal on the frequency of excitation allows us to analyze the dispersion law with high precision. Bi12TiO20 and Bi12GeO20 single crystals are used for the investigations, and the dependences of Omega(k) on K, on external field, on index of modulation, and on light intensity are studied. The experimentally observed relation Omega(k)proportional to 1/K is in excellent agreement with theory. A contribution of nonlinear effects to the spectrum of photorefractive waves is discussed. [S1050-2947(99)00909-9].