Investigations on the catastrophic damage in multilayer dielectric films

HfO2/SiO2 coatings are always fluence-limited by a class of rare catastrophic failures induced by a nanosecond laser with a wavelength of 1053 nm. The catastrophic damage in HfO2/SiO2 coatings behaves as the damage growth with repeated laser irradiation, and thus eventually limits the mirror performance. Understanding the damage processes and mechanisms associated with the catastrophic damage are important for reducing the occurrence of the catastrophic failure and allowing the HfO2/SiO2 coatings to survive at the high fluence required by high laser systems. The rough damage behavior of the catastrophic failure at the proper critical fluence is present. The pit and delamination in the catastrophic failure are investigated to find the possible reasons leading to the catastrophic failure. The experimental results indicate that nodular defect originated from the substrate easily incurs the catastrophic damage. The electric field enhancements of the pit and the substrate impurities may contribute to this phenomenon. The delamination is always present on the left of the pit when laser irradiates from left to right at oblique incidence, which may be related to the plasma plume toward the laser incidence.