Subharmonic generation in photorefractive crystals: Application of theory to experiment

The main results of the theory of spatial subharmonics in photorefractive crystals are summarized. The theory shows that Kukhtarev's equations for the photorefractive response are not valid for sufficiently large values of the mobility-lifetime product and for certain parameters (external field, frequency detuning, grating vector, pump intensity) of a two-beam experiment. The solution for the space-charge field including only the fundamental and the higher harmonics is not stable against the generation of new spatial frequencies. The condition of subharmonic generation and the main characteristics of the subharmonics are expressed by standard experimental and crystal parameters. Good quantitative agreement between theory and experiment is obtained. The prospects of further investigations of subharmonics are discussed.