Characterization Methods of the Heat-Affected Zone During CO2 Laser Processing of Fused Silica Optical Components

During the CO2 laser processing of fused silica optical components, rapid heating to localized high temperatures followed by fast cooling easily induces thermal accumulation effects and forms a heat-affected zone (HAZ). Material modifications occurring within the HAZ (e.g., material densification, changes in fictive temperature, and the generation of residual stress) enhance local absorption of the transmitted laser, thereby increasing the risk of re-damage to the components and compromising their service life. This paper systematically reviews the characterization methods and research progress regarding the HAZ generated during CO2 laser processing of fused silica optics. In terms of macroscopic characterization, the paper first reviews surface and subsurface morphologies and defects observed via optical and scanning electron microscopy (SEM). It then details measurements of absorption properties, molecular structural evolution, and fictive temperature spatial distributions using confocal Raman, photothermal, Fourier-transform infrared (FTIR), and X-ray diffraction (XRD) techniques. Finally, it addresses the evaluation and mitigation of residual stress fields in the HAZ based on fictive temperature and photoelasticity. In terms of microscopic characterization, it summarizes the progress of molecular dynamics (MD) simulations in revealing the atomic-scale evolution of the fused silica network under laser irradiation. It is concluded that reducing thermal accumulation and temperature gradients during laser processing, appropriately controlling the HAZ extent, and suppressing residual stress through methods such as annealing are key to improving the processing quality and operational reliability of fused silica optical components. Future work should further leverage molecular dynamics simulations to conduct precise calculations of microstructural changes as well as coupled calculations bridging microscopic and macroscopic scales, providing theoretical guidance for optimizing laser processing parameters, suppressing the HAZ, and eliminating residual stress.