Light-induced absorption changes in reduced lithium niobate

Abstract

Reduced LiNbO3 crystals change their optical absorption under illumination with blue or green pump light. We measure the dependence of this effect on pump intensity I at different probe wavelengths. Steady-state absorption changes and build-up velocities are found to be proportional to the square root of I. Rates of relaxation towards equilibrium in the dark increase exponentially with temperature. Our experimental results can be well described by light-induced dissociation of bipolarons into small polarons unstable at room temperature.