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

•The mitigated damages of fused silica with minimal re-deposit, negligible residual stress and raised-rim less than 10 nm can be directly machined by shortening the pulse length of CO2 laser to tightly confine the heat affected zones.•Raman spectrum measurements show that the heat affected zone of mitigated damages is densified as a result of fictive temperature increasing of fused silica due to the rapid heating and cooling induced by the CO2 laser pulse.•The numerical simulation of the heat affected zone in the form of fictive temperature modification of fused silica indicates that tightly confined heat affected zones can be formed by minimizing the thermal diffusion length and mainly induced by intrinsic absorption depth of the CO2 laser.