Propagation of point defects in SiO2/Al2O3 anti-reflection coatings under multi-pulse laser irradiation

The performance degradation of optical materials is a critical issue that limits the long-term stable operation of high-power optical systems. To maintain the stability of laser system, it is crucial to reveal the degradation mechanism of optical components. In this study, in situ photoluminescence (PL) spectra, transmittance spectra and laser-induced damage threshold (LIDT) detect were employed to investigate the causes of the optical performance degradation in SiO2/Al2O3 anti-reflection (AR) coating. Additionally, cathodoluminescence (CL) spectra was used to reveal the distribution characteristics and the propagation law of point defects. The results indicated that the propagation of point defects induced by multi-pulse laser irradiation is the primary cause of the performance degradation in AR coatings. Seven intrinsic point defects were identified and their proportional relationships were quantitatively determined. Non-bridging oxygen hole center (NBOHC) is the point defect with the largest proportion. The SiO2 substrate is the primary position for the propagation of point defects. Selftrapped exciton (STE), NBOHC and peroxy radical (POR) have a more significant impact on optical performances due to their higher propagation rates. This study reveals the propagation laws of point defects at the atomic scale and provides new insights into the performance degradation induced by multi-pulse laser irradiation.