HOLOGRAPHIC GRATING FORMATION IN PHOTOREFRACTIVE CRYSTALS WITH ARBITRARY ELECTRON-TRANSPORT LENGTHS

The time development of optically induced refractive-index hologram gratings in photrefractive electro-optic crystals such as lithium niobate and bismuth silicon oxide is analyzed allowing arbitrary electron-transport lengths and nonsinusoidal grating shapes. In this analysis, diffusion and drift in applied and space-charge fields as well as the bulk photovoltaic effect (when applicable) are included. Results for the photoinduced space-charge field are presented for a range of realistic experimental conditions. It is shown that the spatial phase of the space-charge field and therefore the beam coupling is strongly dependent on the electron-transport lengths, whereas the magnitude of the field and therefore the diffraction efficiency is not dependent. It is shown that for paraelectric materials (such as BSO) the results of short- and long-transport-length analyses must converge for long recording times (saturation).