Effect of Cd2+ Doping on Laser Damage Threshold and Optical Performance of KDP Crystals

Abstract

Cd²⁺-doped potassium dihydrogen phosphate single crystals are prepared by “point seed” method. A significant disparity is identified in Cd concentrations between pyramidal and prismatic samples, with prismatic samples exhibiting higher levels. The ultraviolet–visible (UV–vis) spectra indicate that KDP crystals doped with trace Cd²⁺ exhibit increased transmittance, while those with excessive Cd²⁺ show reduced transmittance in the UV region. Additionally, excessive Cd²⁺ causes light absorption in the band ≈220 nm. Structural analysis is conducted utilizing infrared spectroscopy (IR). The results indicate that Cd²⁺ doping distorts the chemical bonding in KDP crystals and reduces their structural stability. A detailed analysis of the photoluminescence (PL) spectro copy results shows that Cd²⁺ in KDP crystals is related to increased defect concentration. The laser-induced damage threshold (LIDT) results demonstrate that the LIDT of crystals decreases with increasing Cd²⁺ doping concentration. The Cd0-Py sample demonstrates the highest LIDT value of 16.75 J cm⁻² under the R-on-1 condition. The value of Cd1000-Py sample decreases to 7.46 J cm⁻² in the same mode, primarily attributable to the comparatively elevated concentration of micro defects. Differential incorporation of Cd²⁺ into pyramidal versus prismatic sectors is proposed, as substitutional and interstitial defects, accounts for the decrease of laser-induced damage performance of KDP crystal based on the findings and prior reports.