Femtosecond laser-induced damage on the surface of KDP crystals by Zn2+ doping

An experimental and numerical study of femtosecond laser-induced surface damage of the potassium dihydrogen phosphate (KDP) crystals doped with Zn²⁺ is presented. Based on COMSOL® Multiphysics 6.1, electron-lattice nonequilibrium interactions were simulated to obtain the temporal evolution of electron concentration, electron temperature, and lattice temperature. The surface damage profile of the samples was analyzed by optical microscopy, and the single-pulse damage threshold was determined. Raman spectra shows that the chemistry of the crystals appeared to remain constant before and after the damage. Single-particle fluorescence spectroscopy indicates that the fluorescence intensity first decreased and then increased with increasing doping concentration. However, the laser-induced damage threshold (LIDT) was negatively correlated with the defect concentration, which may be a result of the synergistic effect of nonlinear adsorption and defect concentration. The above work attempts to give a rational explanation for the process of femtosecond laser damage to the surface of KDP crystals.