First-principles investigation on the impact of interstitial Mg in KDP crystals on laser-induced damage threshold

Abstract

Potassium dihydrogen phosphate (KDP) crystals play a crucial role in inertial confinement fusion (ICF), and their damage threshold has become a significant area of research. This work employs first-principles methods to investigate whether the lattice distortion and optical property caused by Mg_i in KDP crystals have a negative effect on the laser-induced damage threshold (LIDT). The formation energies of defects were corrected using the FNV method. Two defect transition energy levels within the band gap were obtained: ε(0/+1) = 2.45eV and ε(+1/+2) = 3.86eV. The presence of interstitial Mg caused large lattice distortion, which aligns with experimental findings. By considering electron-phonon coupling and introducing the Huang-Rhys factor, we obtained the photoluminescence absorption spectrum. The calculated absorption peaks locate at 352 nm, 273 nm, 196 nm, and 188 nm, respectively. The presence of the new optical absorption and large lattice distortion will reduce its LIDT in KDP crystal.