Defect structure and optical damage resistance of Hf:Fe:LiNbO3 crystals

A series of Hf:Fe:LiNbO3 crystals were grown by the Czochralski technique with various doping concentrations of HfO2. Their defect structures were analyzed by the UV–visible absorption spectra and infrared absorption spectra. The optical damage resistance of Hf:Fe:LiNbO3 crystals was measured by the photo-induced birefringence change and the transmitted light spot distortion method. The results show that the optical damage resistance ability of Hf:Fe:LiNbO3 crystals enhances remarkably with the HfO2 concentration increasing when the HfO2 concentration is lower than its threshold concentration (4 mol%). However, when the HfO2 concentration exceeds its threshold concentration, the optical damage resistance ability of the crystals returns to decrease. This unusual behavior is explained by using the photovoltaic field produced in the crystals.