Material migration and damage characteristics of fused silica optical surface treated by CO2 laser/short – pulse ultraviolet laser

Abstract

Fused silica optics, as key components in high - power laser systems, are prone to be damaged under short - pulse ultraviolet (UV) laser irradiation. CO2 laser is usually used to repair the laser damage and extend the service life of optics. However, the anti - laser damage characteristics of repaired substrates sometimes can’t meet the expectation. To facilitate better application of CO2 laser repairing method, this work studied the CO2 laser irradiating mechanism of fused silica in detail and investigated the damage characteristics of repaired optical surface through experiments. Firstly, finite element level - set (FELS) method is adopted to simulate CO2 laser irradiating process. The simulation showed that CO2 laser irradiation would cause molten material migration, vapor material deposition and affect the formation of residual stress. Various tests of morphology, residual stress, and photo - thermal absorption were conducted to study the changes of laser damage characteristics of repaired craters. The experimental results presented that molten materials migration and vapor materials re deposition occurred in CO2 laser irradiation, which would promote the formation of residual stress, cause stronger laser absorption, or even induce laser damage. Through the experiment, accuracy of simulation was verified further. In this work, the CO2 laser repairing mechanism of fused silica and laser damage characteristics of repaired optics are clarified through FELS simulation and experiments. Relative results can provide a certain technical support for the performance improvement of repaired fused silica optics.