High precision laser ablation of fused silica using pulsed CO<sub>2</sub> laser

Abstract

Laser polishing is a novel processing method which can achieve a super-smooth surface of an optical component. However, there are residual ripples and surface distortions after laser polishing. High precision laser ablation can be used to correct the residual ripple and shape of the component, making it a promising figuring method. In this paper, the experiment of high precision laser ablation of fused silica was carried out with pulsed CO2 laser. It is verified that high-precision uniform ablation in a local region can be achieved by controlling the laser overlap rate, and different nanometer ablation depths can be obtained by controlling the laser power density. However, it has been found that there is thermal accumulation and over-ablation during the laser ablation process. A three-dimensional numerical model was established to simulate the process of pulsed CO2 laser scanning on a fused silica surface. The surface temperature distribution and evolution of fused silica with different overlap rates and pulse repetition frequencies were analyzed. The numerical results show that the increase of the overlap rate could lead to over-ablation. With a suitable overlap rate, the high pulse repetition frequency could result in significant heat accumulation.