Abstract
Freshly deposited aluminum prepared under optimum conditions was overcoated with MgF2 and LiF films at various deposition rates and substrate temperatures. The thickness of the dielectric films was precisely controlled by reflectance measurements at λ = 1216 Å. The thicknesses of the MgF2 and LiF films were chosen to give highest reflectance at 1216 Å and 1026 Å, respectively, and the reflectance was measured from 1000 Å to 2000 Å. Highest reflectance for aluminum overcoated with MgF2 was obtained with a MgF2 deposition rate of about 45 Å/sec. When the MgF2 deposition rate was decreased from 45 Å/sec to 5 Å/sec, the reflectance at 1216 Å decreased from 85.7% to 78%. A decrease in reflectance was also noticeable for deposition rates higher than 45 Å/sec. No improvement in reflectance was noted for substrate temperatures up to 100°C, and at temperatures above 100°C the reflectance decreased. The reflectance of aluminum overcoated with LiF did not show a measurable dependence on the LiF deposition rate, but the reflectance was strongly influenced by the substrate temperature. Highest reflectance at 1026 Å was obtained when the LiF was deposited at a substrate temperature of 100°C. The effects of aging on the reflectance of the mirrors are discussed.
© 1972 Optical Society of America
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