Improved aluminum coatings for the ultraviolet

The reflectance values published by Hass (1955) for highly-reflective aluminum coatings with and without dielectric overcoats for use in the UV region are contradicted by evaporated aluminum coatings produced under a wide range of deposition conditions. The reflectances of these coatings seem to be independent of both evaporation pressure and deposition time and rate, and do not have the characteristic decrease in reflectance with increasing wavelength. Attention is given to the origin of a reflectance dip in all the coatings examined, near 300 nm, which has not been reported previously and appears to be caused by neither adsorbed layers on the film nor trapped impurities within it.