LASER-INDUCED TRANSIENT GRATINGS IN LINBO3-FE

Holographic gratings are recorded in LiNbO3:Fe using frequency-doubled pulses of a Q-switched Nd:YAG laser (light wavelength lambda = 532 nm, pulse duration t(p) = 20 ns). We monitor diffraction efficiencies of the holograms during and several milliseconds after exposure. Variations of Fe2+ concentration, light intensity, and fringe spacing show that different types of gratings are involved: amplitude, thermo-optic, pyroelectric, and space-charge gratings. The influence of the internal pyroelectric field on the light-induced charge transport is discussed in terms of a two-center model. Pyroelectric and bulk photovoltaic effect partially compensate each other. In LiNBO3:Fe the photovoltaic effect is the dominant charge driving force for our recording conditions.