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 coherent light beams while using the running grating technique [M.P. Petrov, S.I. Stepanov and A.V. Khomenko, Photorefractive Crystals in Coherent Optical Systems, Springer Series in Optical Sciences (Springer, 1991); P. Refregier, L. Solymar, H. Rajbenbach and J.P. Huignard, J. Appl. Phys. 58 (1985) 45], as a function of detuning frequency and beam ratio ß in photorefractive Bi12SiO20. It is shown that for ß > 0.05, in addition to the main peak in the frequency dependence of the amplitude, there is an additional peak of lower frequency which, as a rule, dominates the main peak. The position of the main peak depends on ß. The experimental results are in good agreement with the theoretical analysis and the general ideas about excitation and nonlinear interaction of weakly damped space-charge waves

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

We analyze theoretically the photorefractive response of periodically poled lithium niobate (PPLN) taking into account spatial fluctuations of its domain structure. It is shown that these fluctuations strongly affect the amplitude of space-charge field in the limit of small photorefractive grating vectors. 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 sensitive 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 samples

Excitation of higher spatial harmonics by a moving light pattern in sillenites

We investigate numerically the dependence of higher harmonics of the space-charge field on the detuning frequency between the pump waves, which form a running interference pattern. Bistability and hysteresis of harmonics are predicted for a contrast of the interference pattern m =(0.25-0.3). For contrasts m˜1 and small detuning frequencies we show the existence of a narrow resonance, connected with the nonlinear excitation of a slowly decreasing sequence of spatial harmonics. For experiments we use a BSO crystal in the optical configuration which avoids nonlinear optical distortions. The experimental data show good qualitative agreement with theory

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

We analyze theoretically the photorefractive response of periodically poled lithium niobate (PPLN) taking into account spatial fluctuations of its domain structure. It is shown that these fluctuations strongly affect the amplitude of space-charge field in the limit of small photorefractive grating vectors. 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 sensitive 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 samples