In:Tm:LiNbO3 crystals were grown by the Czochralski technique with fixed concentrations of Tm2O3 and differing
concentrations of In2O3. Their ultraviolet-visible absorption spectra were measured in order to investigate their defect
structures and their optical damage resistance was characterized by the transmission light spot distortion method. The
results show that the optical damage resistance of the In:Tm:LiNbO3 crystals improves with the doping concentration of
In2O3 increasing. The dependence of the optical damage resistance on the defect structure of In:Tm:LiNbO3 crystals is
discussed in detail.