Photorefraction Resistance of Na2O-Doped Lithium Niobate Single Crystals

Na2O-doped (up to 3 mol% Na in the melt) LiNbO3 crystals have been grown by the Czochraski method. The experimental results show that Na2O dopants can increase the ability of LiNbO3 to resist light-induced optical damage, but the photorefraction of LiNbO3:Na(3 mol%) is larger than that of LiNbO3:Na (1 mol%) and the absorption edge of the former crystal has a longer wavelength compared with that of the latter. These two abnormal phenomena were interpreted as that some ilmenite structure (NaNbO3) regions are formed in doped LiNbO3 crystals with the increasing dopant concentration of Na2O.