Highly reflective aluminum coatings or aluminum coatings with dielectric overcoats are frequently used in the ultraviolet. The reflectance values published by Hass and his group are generally accepted for this uv region. We have produced evaporated aluminum coatings for a wide range of deposition conditions and none of our coatings exhibit the Hass reflectance characteristics. The reflectance of our coatings appear to be independent of the evaporation pressure and deposition time or rate. Our coatings do not have the characteristic decrease in reflectance with decreasing wavelength. Our main attention has been focused on the origin of a reflectance dip for each of our coatings near 300 nm. This dip has apparently not been reported before and does not appear to be due to adsorbed layers on the film or due to trapped impurities within the film.
David F. Edwards,
"Improved Aluminum Coatings For The Ultraviolet", Proc. SPIE 0288, Los Alamos Conf on Optics '81, (30 December 1981); doi: 10.1117/12.932016; https://doi.org/10.1117/12.932016