Ejecta distribution and transport property of fused silica under the laser shock loading

RQ Shen and QS Bai and YH Li and YB Guo and FH Zhang, JOURNAL OF APPLIED PHYSICS, 127, 245114 (2020).

DOI: 10.1063/1.5144187

Laser-induced particle ejection on the exit surface of fused silica serves as an important contaminant source in a high-power laser system. The transport process of molten silica particles in a gas environment or vacuum is important in understanding the change in size and temperature of silica particles, which influence the ultra-clean manufacturing of optical components. In this paper, the ejection process of fused silica is investigated using molecular dynamics simulation. The results show that the geometry of a surface scratch influences the mass of the microjet. With shallower groove depth and a smaller vortex angle, the mass of the microjet is less under shock loading. The size of ejected particles tends to decrease gradually and does not change any more eventually. Besides, these particles become dispersed during the transport process in a vacuum. On the other hand, background gas suppresses the particle flow and slows down the particle flow. As the ejected particles compress gas, vapor and small clusters (N < 50) are stripped from the microjet continuously. Eventually, the number of nanoparticles that exceed the free surface decreases to zero. The stripped small clusters behind the head of the microjet recombine with other clusters, which change the volume density of ejected particles near the free surface. The higher velocity of ejected particles induces a stronger gas stripping effect, which makes an increase in the number of small clusters (N < 50). The results can help understand the behavior of particle ejection and the transport process of silica particles in a gas environment or vacuum, especially in the field of laser-induced particle ejection on the exit surface or the laser ablation of fused silica producing aerosol.

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