SPATIOTEMPORAL RESONANCE IN GENERATION OF SUBHARMONICS, SUM AND DIFFERENCE FREQUENCIES IN PHOTOREFRACTIVE CRYSTALS

Illumination of a photorefractive crystal by light containing two interference patterns (generally running) is considered. As well as linear terms in the response, the nonlinear ones are calculated, corresponding to sum and difference spatial frequencies. Efficient recording of those nonlinear gratings due to temporal phase-matching, i.e. phase-locked detection, is predicted under the application of spatially homogeneous field with DC and/or with sinusoidal time dependence. Thresholds for parametric instabilities of the types of subharmonic generation are calculated for different cases.