Rigorous three-dimensional theory of subharmonic instability in sillenites

We propose a theory of the instability of the space-charge field induced in a semiconductor by the movement of light fringes against subharmonic generation. A crucial element of this theory is taking into account three-dimensional perturbations and higher spatial harmonics of the space-charge field. It is shown that, irrespective of fringe contrast and velocity, the strongest instability corresponds to the excitation of subharmonics that are not split in the transverse direction. The theory is applied to experimental data on subharmonic generation in sillenites.