Atomic simulation of surface damage of fused silica under laser irradiation

Abstract

Fused silica optical element is the core component of the inertial confinement nuclear fusion ignition device. Due to the requirement of ignition conditions of the device for high power laser, the damage to fused silica optical element under strong laser is the key to restricting the operation of the ignition device. Therefore, the study of the surface damage of fused silica irradiated by laser is crucial to the development of the ignition device for inertial confinement nuclear fusion. In this paper, large-scale non-equilibrium molecular dynamics simulation method and micro-structure analysis technology suitable for dynamic process are proposed to study the damage process of fused silica surface under laser loading. Based on the theoretical study of high-temperature plasma fireball model, the damage of high-temperature fused silica plasma ball to surface is simulated. By tracking the local structure, temperature distribution and surface morphology, the factors affecting the surface damage of fused silica are analyzed. Our research results show that the size, distance from the surface, and temperature of high-temperature fused silica balls have important effects on the surface damage. We find that there are two different damage modes under the combined effect of the above factors. One is related to a rapid damage process, generating U-shaped voids and no further obvious damages after the surface spraying, and the other is dependent of a slow damage process: continuously expanding and resulting in a larger damage area. The surface morphologies formed by these two damage modes are consistent with the two typical damage morphologies observed in the experiments. This research can provide a guidance for understanding the complex damage process in fused silica under laser irradiation.