Laser-damage threshold of Sc2O3/SiO2 high reflector coatings for a laser wavelength of 355 nm

Highly damage-resistant optical coatings are essential for the development of high output energy UV lasers. The authors have prepared Sc2O3/SiO2 high reflector (HR) coatings and measured some of their characteristics (laser-damage threshold for short-pulsed laser of wavelength 355 nm, the effect of a coating layer on the threshold, stress of the coating). The average damage thresholds on fused SiO2, BK-7 and sapphire substrates were 2.9, 3.6 and 3.5 J cm−2 respectively. An SiO2 coating layer improved the threshold by 25%, while an MgF2 layer hardly changed the threshold. When the coating designs were the same, the average damage thresholds of the HR coatings on the BK-7 or sapphire substrate were 20%–25% greater than those on the SiO2 substrate. The (compressive) stress of the HR coating on the SiO2 substrate was 470 kgf cm−2.