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Influence of Deposition Parameters on Laser Damage Threshold of 355-nm Scandium Oxide-Magnesium Fluoride High-Reflector Coatings

The experimental results of the laser-induced damage thresholds of Sc2O3/MgF2 high-reflector (HR) coatings for an UV (355-nm, 0.4-ns) pulsed laser have been shown. The deposition parameters have been optimized by use of 5-layer semitransparent coatings, with the distribution of the standing-wave electric-field being similar to that of the HR coatings. For the 5-layer coatings, their threshold values were found to depend on the deposition parameters and the absorption; the coatings with low absorption had high damage threshold. Based on these results, the HR coatings were fabricated on fused silica, BK7 and sapphire substrates, and their thresholds have been measured. The highest average threshold on each substrate have been 3.5, 4.2 and 3.8 J/cm2, respectively.