Laser damage comparisons of E-beam evaporated HfO2/SiO2 antireflection coatings at 0% and 40% relative humidity for 532 nm and 1064 nm

Antireflection coatings, containing alternating layers of hafnia (HfO2) and silica (SiO2), were deposited using electron beam (e-beam) evaporation for use in laser operations at 532 nm and 1064 nm in the nanosecond regime. The e-beam evaporation process produces coatings that are porous and therefore absorb water from the ambient environment. Consequently, humidity may affect the spectral performance of the coatings, and the laser damage resistance of the coatings may be affected as well. The purpose of this study was to compare the laser-induced damage thresholds of the antireflection coatings measured in the ambient environment at 0% and 40.5% relative humidity. At 1064 nm, the laserinduced damage thresholds at 0% and 40.5% relative humidity were almost the same. However, at 532 nm, the laserinduced damage thresholds at 40.5% relative humidity were nearly twice as high as those measured at 0% relative humidity. This indicates that humidity can inhibit lower-fluence precursors that would lead to laser damage at 532 nm in the nanosecond regime, thereby improving the durability of the coatings in a humid environment.