Abstract
An investigation was made of the effects of aluminum purity, substrate temperature, aging, and ultraviolet irradiation on the reflectance of coatings of aluminum deposited on glass by evaporation. The wavelength range covered was 900–2200 A. Data are presented supporting the following conclusions. Whenever aluminum mirrors or diffraction gratings of the highest reflectance are required for use in the extreme ultraviolet, it is important that they be produced from the purest grade of aluminum (99.99%) on a nonheated substrate. Growth of the oxide should be retarded, so far as possible, by storing the coatings in a dessicator, rather than leaving them exposed to normal room air. If left in an unevacuated spectrograph some drying agent should be introduced. Intense ultraviolet irradiation should be avoided as much as possible, especially if water vapor is present. For use at wavelengths below 1100 A heavily anodized aluminum may be preferred to fresh aluminum.
© 1957 Optical Society of America
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