Light-induced absorption and its relaxation under illumination of continuous wave ultraviolet light in Mn-doped near-stoichiometric LiNbO₃

The steady-state light-induced absorption and the temporal relaxation behavior under illumination of cw ultraviolet light in Mn-doped near-stoichiometric LiNbO₃ with different crystal compositions are investigated. The ultraviolet-light-induced absorption has been assigned to small polarons Nb_Li⁴⁺ by measuring the absorption spectra at room temperature. The dependences of relaxation behaviors (time constant and stretching factor) of light-induced absorption on various illumination conditions (intensity, polarization) and temperature are presented, which are very different from those observed in Fe-doped LiNbO₃ illuminated with highly intense light pulse, though the temporal relaxation follows the same stretched-exponential decay behavior in both cases. The results are explained reasonably by using the model of distance-dependent electron transition probabilities between localized deep traps and small polarons without any additional assumptions, and discussed to tailor doped near-stoichiometric LiNbO₃ crystals for two-color holographic recording with cw laser light.