REDUCTION OF LASER-INDUCED DARK TRACES IN LINBO3-MG AND LINBO3-ZN BY HEAT-TREATMENT

The dark traces induced by high-power laser radiation in LiNbO3:Mg and LiNbO3:Zn are found to be reduced by annealing the crystals in an O-2 atmosphere. Most of the decrease of the second-harmonic generation ef ficiency eta for 1064-532 nm conversion due to dark traces can be reco vered in heat-treated crystals. The transmission loss spectra Delta T( lambda) of dark traces show a complex absorption band ranging from 365 nm to near infrared, which can be decomposed into three main peaks at 3.1: 2.5, and 1.6 eV. Maximum transmission loss due to dark traces af ter 1200 shots with an input power density of 18 MW/cm(2) is 17% and 2 5% for as-grown LiNbO3:Zn and LiNbO3:Mg crystals respectively, and it is reduced to 4.6% and 3.8% respectively for heat-treated crystals. (C ) 1996 American Institute of Physics.