Toward little heat-affected area of fused silica materials using short pulse and high power CO₂ laser

As a rapid and efficient processing technology, CO₂ laser processing has been applied to remove fused silica materials. However, thermal effect caused by CO₂ laser would lead to thermal modification layer, thermal deformation and residual stress in processed fused silica optics. To reduce the thermal effect, high power and short pulse CO₂ laser is applied to remove the surface material of fused silica. In this work, a model coupling the physical processes of heat transfer and phase transition was established to simulate the complex interaction of CO₂ laser with fused silica. Then, the model was applied to investigate the evolutions of temperature distribution and surface morphology involved in the laser ablating and melting processes. The results indicate that with the increase of laser power and decrease of pulse width, positive effect would take place that the radius-depth ratio of ablating area increases and the heat-affected area becomes smaller. For the application of CO₂ laser with 0.2 μs pulse width and 800 kW peak power, fused silica material would quickly reach the ablation state. The ablation depth is less than 1 μm, and the thickness of heat-affected area is about 80 nm. It means that the high power and short pulse CO₂ laser is equivalent to a hot grinding ball head, which can remove the material rapidly with small heat-affected area on fused silica surface. The simulation results of line scanning processing with CO₂ laser were finally compared with the experiment ones, which verified the feasibility of the established model. The suggestions and prospective for improving the model were put forward as well.