SPATIAL SUBHARMONIC INSTABILITIES IN PHOTOREFRACTIVE CRYSTALS

The parametric generation of spatial subharmonic gratings in photorefr active crystals is studied based on an evolution equation for the spac e charge held. It is shown that a Kin subharmonic instability can be r esonantly excited when b = q/(1 + q(2)/n(2)) is satisfied with b and q the detuning parameter and the external de field, respectively. The s pectral widths near the resonances for K/2, K/3 and K/4 subharmonic in stabilities are also given. The theoretical results are compared with previous experiments.