The effects of γ-irradiation on potassium dihydrogen phosphate crystals containing arsenic impurities are investigated with different optical diagnostics, including UV-VIS absorption spectroscopy, photo-thermal common-path interferometer and photoluminescence spectroscopy. The optical absorption spectra indicate that a new broad absorption band near 260 nm appears after γ-irradiation. It is found that the intensity of absorption band increases with the increasing irradiation dose and arsenic impurity concentration. The simulation of radiation defects show that this absorption is assigned to the formation of AsO₄⁴⁻ centers due to arsenic ions substituting for phosphorus ions. Laser-induced damage threshold test is conducted by using 355 nm nanosecond laser pulses. The correlations between arsenic impurity concentration and laser induced damage threshold are presented. The results indicate that the damage performance of the material decreases with the increasing arsenic impurity concentration. Possible mechanisms of the irradiation-induced defects formation under γ-irradiation of KDP crystals are discussed.

Multiparametric raster scanning experiments for KDP crystals are carried out to study the laser conditioning efficiency as a function of laser fluence, fluence step, and pulse sequence by using ultraviolet (UV) laser irradiation with pulse duration of approximately 7 ns. It indicates that damage resistance of KDP can be enhanced after conditioning process. And laser conditioning efficiency depends on the maximal fluence which is below the damage threshold. Raman spectra and photothermal absorption have also been studied on KDP crystals before and after multiparametric laser conditioning. Photothermal absorption data reveal that absorbance of conditioned KDP crystal decreases with the increase of laser fluence and the damage threshold of low absorption area is higher. Raman analysis reveals that the effectiveness of laser conditioning relies mainly on the individual mode of PO4molecule.

No abstract