LOW-FREQUENCY PECULIARITIES OF THE PHOTOREFRACTIVE RESPONSE IN SILLENITES

We investigate experimentally and theoretically the dependence of the amplitude of the spatial fundamental grating, created by a pair of coh erent light beams while using the running grating technique [M.P. Petr ov, S.I. Stepanov and A.V. Khomenko, Photorefractive Crystals in Coher ent Optical Systems, Springer Series in Optical Sciences (Springer, 19 91); P. Refregier, L. Solymar, H. Rajbenbach and J,P, Huignard, J. App l. Phys. 58 (1985) 45], as a function of detuning frequency and beam r atio beta in photorefractive Bi12SiO20. It is shown that for beta grea ter than or equal to 0.05, in addition to the main peak in the frequen cy dependence of the amplitude, there is an additional peak of lower f requency which, as a rule, dominates the main peak. The position of th e main peak depends on beta. The experimental results are in good agre ement with the theoretical analysis and the general ideas about excita tion and nonlinear interaction of weakly damped space-charge waves.