The 266 nm AR coatings consisting of Sc2O3/SiO2 and HfO2/SiO2 were deposited on fused silica and CaF2
substrates. The laser damage resistance (LDR) was measured to determine the laser fluence that a coating can withstand
without damaging when exposed to a large number of pulses. The LDRs of Sc2O3/SiO2 AR coatings were higher than
those of HfO2/SiO2 AR coatings. The absorption, subsurface damage and the surface roughness of the substrates were
measured and were correlated with the LDR of AR coatings. The LDR generally decreased as the subsurface damage
size increased. The substrate with the largest subsurface damage showed the relatively high absorption of ~220 ppm at
266 nm compared to other substrates with the smaller subsurface damage. The LDR of Sc2O3/SiO2 AR coating on it was
the lowest (9.9 J/cm2). No correlation between the surface roughness and the LDR of AR coatings was found. Improving
the polishing process was concluded to be an important factor in increasing the LDR of the AR coating. The laser
damage morphology on AR coating was also studied.
The laser damage resistance (LDR) is a measure of the laser fluence that a coating can withstand without damaging when exposed to a large number of pulses. The LDR of UV coatings has been studied at 266 nm on two common substrate materials. Significantly higher values for the LDR have been measured for the same coating deposited on CaF2 substrate compared to fused silica substrates. Various parameters such as the surface roughness, the absorption and the subsurface damage of these quite different materials were measured in an effort to explain the performance difference. The laser damage morphologies of the coatings were also studied.
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