Exploring multilayer dielectric mirror coating materials for optimizing long-term performance under 351-nm nanosecond pulses

Optical coatings used in transport optics should withstand exposure of the order of ten years and 10^10 pulses. In such long operation, it might be impossible to avoid contamination and optical coating material laser damage. This necessitates the development of materials that not only provide high-damage-initiation threshold and long-term stability of damage-initiation sites, but also avoid damage growth. In this work, we explore two high-index coating materials incorporated in high-reflector multilayer dielectric mirror coatings fabricated with different deposition methods. Under nanosecond pulses at a 351-nm wavelength, we found a systematic difference in the damage-growth thresholds. This indicates that the difference arises from the material properties after exposure to laser damage and the ensuing interaction (such as absorptivity) with the laser pulses. The results highlight that the choice of coating material is critical for reliable long-term operation of ultraviolet beam-transport optics.