Study on optical performance and 532 nm laser damage of rapidly grown KDP crystals

Type II samples were obtained from the adjacent positions of pyramidal sector and prismatic sector in the same potassium dihydrogen phosphate (KDP) single crystal grown by the “point seed” technique under different temperature range and supersaturation. Some samples were annealed at 160 °C for 24 h. The UV–Vis spectra, especially in the ultraviolet region, show the optimal transmitting ability for the KDP crystal which was grown under relative low temperature range. The structural analysis performed by means of Fourier transformed infrared spectroscopy (FTIR) suggests that the crystal lattice of the KDP grown under relative small supersaturation become compact at the molecular level. The results of photoluminescence (PL) emission spectra show that the PL intensity increases with the rise of supersaturation and growth temperature range, which indicates that the concentration of all the detected micro defects in the KDP is abundant. The damage threshold conducted using 532 nm ns laser pulses shows the same trend with the results of PL spectra. The laser-induced damage threshold (LIDT) has been improved with the decrease of growth temperature range and supersaturation, and its variation has the highest correlation with the concentration of hydrogen vacancy defect. In addition, thermal annealing can effectively reduce the concentration of all the detected micro defects in the sample, and LIDT of the samples can be enhanced further after laser sub-threshold annealing.