First principle calculation of damage characteristics of fused silica containing structural defects under short-pulse laser irradiation

Abstract

Fused silica, as an excellent optical material, was widely used in the fabrication of laser optics applied in short-pulse/high-power laser systems. Fused silica containing structural defects was easy to be destroyed under laser irradiation. Deeply understanding the impact of different structural defects on the damage characteristics was of great significance for improving the laser damage threshold of fused silica optics. This work focused on structural defects including Oxygen Deficiency Center (ODC), Non-Bridging Oxygen Hole Center (NBOHC), E’ center, Peroxy Linkage (POL), Peroxy Radical (PDR), and elaborated on its formation laws in detail. The changes of damage characteristics and optical property of fused silica with different structural defects were calculated by first principle method. Taking E’ center defect as example, the band gap of defective silica was 3.1242 eV while that of β silica was 5.61 eV, which meant that electrons were more likely to cross the band gap under laser irradiation, led to electron avalanche and induced laser damage. Meanwhile, the optical properties of fused silica with different structural defects also showed significant difference. The reflectivity of β silica was 0.045, while that of silica with E’ center defects was 0.0715. Under 355nm laser irradiation, the absorption of β silica was 0 cm-1 while that of E’ center defects was 16600 cm-1, the absorptivity increased significantly. The change of optical properties also increased the probability of laser damage. In this work, certain support could be provided for the laser-damage theory of fused silica, and the relevant results could also provide important reference for suppression of structural defects.