Laser-induced photochromic damage in potassium titanyl phosphate

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Abstract
We report studies of photochromic damage induced in KTiOPO4 single crystals by ultraviolet (UV) irradiation with peak intensities from 0.3 to 4.0 MW/cm2. The photochromic damage progressed to asymptotic values which were not linear with respect to UV intensity. Following UV exposure, transparency of damaged crystals recovered completely over tens of hours at room temperature, faster at elevated temperature. UV irradiation at significantly lower peak but higher average power did not produce damage. We also studied photochromic damage occurring during 1.064-μm second-harmonic generation. Fundamental infrared intensities ranged from 1.3 to 5.5 times larger than those producing highest nonlinear frequency conversion efficiency. Damage sites produced by the two methods exhibited similar absorption spectra.