Particle simulation of the laser-induced damage on the KDP crystal optical surface under intense laser irradiation.

• A PIC model is developed to investigate the plasma behaviors in laser damage processes under intense laser irradiation. • The evolution laws of plasma characteristics under intense laser irradiation are proposed to study from various aspects. • The particle ejection and the formation of craters are reproduced and the internal physical mechanisms are obtained. The laser-induced damage on KDP crystal optical surfaces under intense laser irradiation significantly limits the energy outputs of the high-power laser systems in many regions. The energy deposition in the non-heat stage of the laser-induced damage process is regarded as the main energy source, directly determining the laser-induced damage thresholds. It can cause severe damage to the optical surfaces under intense laser irradiation and significantly affect the final damage morphology on the optical surface. Nevertheless, there is still no available model that can well reproduce the behaviors of the plasma in the non-heat stage to reveal the internal physical mechanisms of the non-heat stage currently. Hence, a particle-in-cell (PIC) model is proposed to investigate the behaviors of the plasma in the non-heat stage. Afterward, the feature information of the plasma in the non-heat stage on the KDP crystal optical surface without surface defects under intense laser irradiation has been obtained from three aspects: the electron density, the electron phase-space distribution on the subatomic scale, and the electric field distribution at different times. Then two types of typical damage behaviors of particle ejection and the formation of the damaged craters on optical surfaces under intense laser irradiation are studied based on the developed model. Finally, the plasma behaviors in the processes of particle ejection and the formation of the damaged craters are well reproduced and the internal physical mechanisms of these two types of damage behaviors are obtained. To sum up, this work proposes a PIC model to investigate the plasma behaviors in the non-heat stage. Based on this, this work reveals the energy deposition mechanism of the non-heat stage in the process of the laser-induced damage on KDP crystal optical surfaces under intense laser irradiation and obtains the interaction laws between the intense laser and the plasma. Moreover, this work opens a door for the study on the non-heat stage of the laser-induced damage process on the optical surface from the subatomic scale, which is beneficial to the revelation of the internal physical mechanisms in the non-heat stage and the solution of the laser-induced damage issues in high-power laser systems. [ABSTRACT FROM AUTHOR]