Molecular dynamics simulation of phase transformation of fused silica under nanoparticle impact: The influence of temperature and impact velocity

In high power laser facilities, the ejected nano- or microparticles from the exit surface of fused silica produced by laser irradiation can cause damage to adjacent optical components because of the high temperature and high impact velocity of particles. Classic molecular dynamics (MD) simulation was conducted to investigate the damage mechanism of optical elements under nanoparticle impact. The increasing temperature coupled with the rising compressive stress facilitated the densification of fused silica, and the over-coordinated silicon atoms were mainly affected by compressive stress until the compressive stress peaked. The influence of local temperature emerged after the compressive stress peaked. The time when the largest volume of heat affected zone appeared was closer to the time when the compressive stress reached the maximum under the higher impact velocity of the nanoparticle. The changes in microstructural characteristics of fused silica showed that the hot compression of fused silica make large ring smaller firstly and then make small ring larger. The findings are instructive in the damage mechanism of optics under the impact of nano- or micro-particle.