Morphology evolution mechanisms and localized structural modification of repaired sites on fused silica optics processed by CO2 laser rapid ablation mitigation

Abstract

In order to in-depth study the surface morphology formation mechanism and surface quality control methods of fused silica repaired sites, numerical simulation and experimental method were firstly used to analyze the process of CO2 laser rapid ablation mitigation, as well as the relationships between processing parameters, repaired angle and surface quality. Then the physical problems of the heat-affected zone, fictive temperature and structure relaxation under the irradiation of pulsed laser were studied through the mathematical model and Raman spectroscopy system. The studies found that the fixed depth morphology was formed starting from the third track’s laser scanning during the processing of fused silica by the pulsed laser that moved according to the arc trajectory. The bottom of the processed morphology presented uneven concave-convex features, which was different from the uniform topography formed by the laser linear scanning processing. The processing angle decreased as the trajectory indentation increased, while there was no clear variation law between the processed surface quality and the indentation. The thickness of the heat-affected zone characterized by the fictive temperature was consistent with the experiment, and it was proportional to the laser pulse width. The negative factors caused by the thermal effect in the laser repair process could be suppressed by reducing the laser pulse width. These studies can provide guidance for the optimization of the CO2 laser repair process and the improvement of the repaired surface quality.