LASER-INDUCED PHOTOCHROMIC DAMAGE IN POTASSIUM TITANYL PHOSPHATE

We report studies of photochromic damage induced in KTiOPO4 single cry stals by ultraviolet (UV) irradiation with peak intensities from 0.3 t o 4.0 MW/cm 2. The photochromic damage progressed to asymptotic values which were not linear with respect to UV intensity. Following UV expo sure, transparency of damaged crystals recovered completely over tens of hours at room temperature, faster at elevated temperature. UV irrad iation at significantly lower peak but higher average power did not pr oduce damage. We also studied photochromic damage occurring during 1.0 64-mum second-harmonic generation. Fundamental infrared intensities ra nged from 1.3 to 5.5 times larger than those producing highest nonline ar frequency conversion efficiency. Damage sites produced by the two m ethods exhibited similar absorption spectra.