Propagation mechanism of E’-center and NBOHC in fused silica induced by gamma-ray irradiation

The degradation of optical transmittance induced by the propagation of point defects in fused silica under gamma-ray irradiation severely threatens the service life of optical components. Existing studies have recognized the importance of this issue through the testing of point defect content before and after irradiation. However, the specific evolution process of these point defects remains unclear. In this paper, experiments and deep potential molecular dynamics (DeePMD) simulations were performed to investigate the essence of degradation in optical transmittance and the propagation mechanism of point defects during gamma-ray irradiation. The results indicate that the optical transmittance significantly decreases within the range of 210 nm to 380 nm, and the degree of change increases with an increase in irradiation dose. The propagation of E’-center and nonbridging oxygen hole center (NBOHC) defect pairs is the fundamental cause for the decrease in transmittance. Both experimental and simulation results indicate that E’-centers and non-bridging oxygen hole centers (NBOHC) originate from the evolution of small rings (n=3 and 4). Additionally, DPMD simulations reveal that under the thermal history induced by gamma-ray irradiation, the formation of small rings (n=3 and 4) occurs at the expense of larger rings (n=6 and 7). The research results provide valuable insights into the propagation mechanism of point defects and contribute to designing the service life of optical components.