Analysis of the decay dynamics of laser-induced gratings in LiNbO_3

Laser-induced refractive-index gratings were created and probed in nominally pure LiNbO3 crystals. The time dependence of the probe beam scattered from the grating during erasure was measured as a function of the crossing angle of the write beams for samples with different thermal annealing histories and as a function of sample temperature. Biexponential grating-decay curves were observed, and the characteristic decay times are interpreted in terms of two types of charge-carrier dynamics contributing to the photorefractive effect. By using a simple charge-relocation model, the charge-carrier densities, relocation rates, and relative trap concentrations contributing to the two grating-decay components were obtained from the data, and their changes with sample temperature and annealing treatment were determined. Measurements of energy transfer through two-wave mixing on both oxidized and reduced samples were used to confirm the two-charge-carrier model.