Influence of pulse length on heat affected zones of evaporatively-mitigated damages of fused silica optics by CO2 laser

Abstract

The influence of pulse length on heat affected zones of evaporatively-mitigated damages was investigated in order to optimize the CO2 laser-based mitigation process of large aperture fused silica optics for high power laser facilities. The evolution of heat affected zones of mitigated damages with increasing pulse length from 5 μs to 90 μs indicates that the thickness of heat affected zone increases with increasing pulse length, but can be tightly confined by shortening the pulse length. The mitigated damages with confined heat affected zones show minimal redeposit, negligible residual stress and rimless. Raman spectra of heat affected zones show that local densification of fused silica occurs as a result of local fictive temperature enhancement induced by the CO2 laser pulse. The numerical simulation of heat affected zone in the form of fictive temperature modification indicates that the tightly-confined heat affected zone can be generated by shortening the pulse length.