Green-induced infrared absorption in MgO doped LiNbO3

Green-induced infrared absorption (GRIIRA) was investigated by a phototherm al technique for undoped and Mg-doped LiNbO3 crystals that have different L i/Nb ratios. Threshold effect on GRIIRA was found, threshold MgO concentrat ions being the same for GRIIRA and photorefraction. We suggest that GRIIRA is associated with the formation of the small polaron that is located on Nb antisite defect. The remarkable decrease of GRIIRA in Mg:LiNbO3 can then b e attributed to the elimination of this intrinsic defect, Nb in Li, followi ng the incorporation of Mg on Li sites. For nonlinear optical applications, LiNbO3 doped with MgO at concentrations over threshold has a combined adva ntage of having almost no GRIIRA and photorefraction. (C) 2001 American Ins titute of Physics.