Numerical simulation on temperature and stress of pulsed laser repairing fused silica defects

Temperature and residual stress distribution of pulsed laser mitigation of fused silica damage is simulated by finite element method. The maximum stress does not appear in the irradiated center but in the periphery because the material at the center has melted. The effects of frequency, duty cycle and beam size on the shape of ablation pit and molten pool are also analyzed. For the same laser power, reducing the above three parameters may lead to the higher temperature at spot center. However, the effects on the size of ablation pit and molten pool are inconsistent. The results show that small laser beam is suitable for small and deep defects while big laser beam is suitable for big and shallow defects. In addition, frequency and duty cycle have significant influence on the ablation. High duty cycle or high frequency may reduce the ablation and melting is predominant mitigation process. Therefore, the mitigation process is mainly ablation for low duty cycle or low frequency. By analysis of elastic-plastic structure, tensile stress is shown in irradiated region and compressive stress is shown outside the region. The maximum tensile stress is not located in the spot center but nearby the melting pool edge.