Laser induced damage threshold measurements at 248nm have been made on thin film deposited aluminium and dielectric overcoated aluminium mirrors. The damage threshold of the aluminium coatings was 0.2Jcm-2. Three dielectric overcoats have been considered, SiO, MgF2 and ThF4. The damage threshold of the SiO and MgF? overcoated aluminium mirrors was about 0.2 - 0.25Jcm-2. The ThF4 overcoated aluminium mirrors with reflectivities at 248nm comparable to the MgF2 and SiO overcoated aluminium mirrors had damage thresholds of 0.4Jcm-2. The influence of U.V. irradiation on the U.V. reflectivity and stoichiometry of the SiO overcoated aluminium mirrors was also investigated. Improvements in reflectivity of 20% at wavelengths below 250nm were observed.
Stephen S. Wiseall,
David C. Emmony,
"Ultra-Violet Laser Damage In Aluminium Mirrors", Proc. SPIE 0401, Thin Film Technologies I, (28 November 1983); doi: 10.1117/12.935528; https://doi.org/10.1117/12.935528