Transient dynamic behavior during nanosecond laser-induced damage initiated by surface defects on KDP crystals with simulation and experimental method

The issues of laser-induced damage of transparent dielectric optics severely limit the development of large laser systems. In order to explore the mechanism of nanosecond laser damage on KDP surface, a multi-physics coupling dynamics model and a time resolved detection system were developed to obtain the transient dynamic behaviors of laser damage. The behaviors of laser energy transmission, thermal field distribution and damage morphology during nanosecond laser irradiation on KDP surface were simulated. It is found that the enhancement of light intensity caused by surface defect plays an important role in the initial energy deposition and damage initiation of the laser irradiation area. The evolution of the temperature field and fluid flow during subsequent laser irradiation contributes to the laser damage process. The simulated evolution of heat absorption source is verified by the transient images of local defect-induced laser damage captured by the ultra-fast experimental detection system. This work provides further insights in explaining the laserinduced damage by surface defects on KDP crystals.