First Principles Study of Vacancy Defects in KDP and DKDP Crystals

Potassium dihydrogen phosphate (KDP) and its deuterated analog (DKDP) are widely used in high-power solid-state laser systems. However, in actual use, they suffer a high risk of damage due to defects that introduced in production and processing. Among them, vacancy defects and dehydration defects are the most common ones exists in crystal growth and processing. In this paper, we start with first principles and conduct theoretical calculations on the above defects. A PBE method is used to calculate the band gap and optical properties of crystal unit containing defects. The results indicate that the presence of defects in the crystal will significantly enhance the laser deposition rate and greatly increases the risk of two-photon absorption ionization, which serves as the origin of crystal damage. The calculations revealed that H-vacancy defects and dehydration defects have the most significant impact on the band gap of KDP/DKDP crystals, making them more prone to allowing laser energy to exploit these vulnerabilities and thereby induce damage.