A. Shumelyuk et al., Multiline coherent oscillation in photorefractive crystals with two species of movable carriers, APP PHYS B, 68(5), 1999, pp. 959-966
The coherent oscillation, because of nearly degenerate four-wave mixing in
photorefractive crystals with two types of movable charge carriers, occurs
at two spectral lines symmetrically shifted with respect to the pump freque
ncy. Consequently the output oscillation exhibits the high contrast intensi
ty modulation. The frequency separation of two oscillation modes land modul
ation frequency of the output intensity) depend on the incident light inten
sity and spatial frequency of the developing grating. A model is presented
explaining this typo of oscillation by the two-maxima shape of the gain spe
ctrum in crystals with sufficiently different relaxation times of two space
-charge gratings, one formed by movable electrons and the other one by mova
ble holes. The experimental data for coherent oscillator with tin hypothiod
iphosphate (Sn2P2S6) an in reasonable quantitative agreement with the calcu
lations.