Surface damage evolution of KDP crystals induced by conical cracks under irradiation of nanosecond laser

The potassium dihydrogen phosphate (KDP) crystals suffer from nanosecond pulse laser irradiation and are susceptible to damage during the operation of ICF system. In particular, the microcracks on the surface of KDP crystals caused by the single-point diamond fly-cutting (SPDF) process are more likely to cause serious damage under the subsequent laser irradiation. However, the mechanism of laser damage is still unclear. A model that can well represents the laser damage response is very important to reveal the mechanism of laser-induced damage. In this work, the electromagnetic field, stress field and temperature field are coupled, the mechanical characteristics of KDP material are considered, and the reasonable strength equation is applied to model the laser damage response of KDP crystal. Then, the conical crack is taken as an example to explore the laser damage response process of KDP crystal caused by surface defects under laser irradiation. It is found that the surface conical cracks have a great influence on the response process and the morphological characteristics of the laser damage. The existence of surface conical crack defects would lead to the extension of the longitudinal cracks beneath the damage crater, which has great disadvantages for the repairing of the laser damage sites. This work is of great guidance for avoiding the defects-induced damage and improving the service life of the crystal applied in ICF systems.