Modulations of nonideal repaired damage sites irradiated by CO2 laser at different parameters

Local CO2 laser processing was reported to effectively mitigate the laser-induced damage growth of 3ω fused silica optics. Herein, combined with the experimental observations, the light intensification of repaired damage sites irradiated at different laser powers and beam sizes were revealed by using three-dimensional finite-difference time-domain method. Two typical nonideal repaired damage sites, with raised rim as well as with concave rim, were discussed. Numerical simulation results show that crater with raised rim generate much greater modulation than the other one. With the laser beam size increasing, the modulation for raised rim crater monotonously increases, while the modulation for concave rim crater increases firstly and then keeps decreasing in the following. On the other hand, the light intensification undergoes decreasing firstly and then increasing when laser power increases. Under the same parameters, it is shown that the modulation of the ideal Gaussian profile is the weakest of all. For the normal incident irradiation at 355 nm laser, the light intensity enhancement factors of the raised and concave rim can be as high as 7.13 and 25.04, respectively. To effectively arrest the damage growth and prolong service life of the optics, Gaussian-typed repaired damage sites should be introduced considering optics recycling.