Modeling of Surface Damage Mitigation in Fused Silica With Carbon Dioxide Laser

A model of surface damage mitigation in fused silica irradiated by CO2 laser is built. Temperature distribution and surface morphology are simulated by finite-element method. It is proposed that a Gaussian crater appears in the mitigation site, which width and depth are dependent on the laser parameters. Following, the effects of frequency, duty cycle, and beam diameter on the size of mitigation are also analyzed. For the same laser power, reducing the above three parameters may lead to higher temperature at the spot center. However, the effects on the size of ablation and melting are inconsistent. The results show that a small laser beam is suitable for smaller and deeper defects, whereas a big laser beam is suitable for bigger and shallower defects. In addition, frequency and duty cycle have a significant influence on the ablation. Large duty cycle or high frequency may reduce the ablation, and thereby, the surface of the ablation profile becomes smoother after melted material recondense. Correspondingly, the mitigation process is mainly ablation for low duty cycle or low frequency.