Abstract
We compared phoconductivity and photovoltaic current density of stoichiometirc, congurent. Mg-doped and Sc-doped LiNbO_3 cystals in order to interpret the mechanism of optical damage. Mg-doped and Sc-doped crystals with high optical damage resistance showed much smaller photovoltaic effect than that in stoichiometric crystal which exhibited considerably large optical damage. The optical damage is probably suppressed by the substitution of Li ion by Mg, Sc, Nb, which cause some change in original dipole structure of stoichiometric LiNbO_3