Abstract

The paper describes a method for preparing reflectance-increasing film pairs of Al₂O₃ and TiO₂ on evaporated aluminum mirrors. With one film pair of Al₂O₃ and TiO₂, each film effectively one-quarter wavelength thick, the visible reflectance of aluminum can be increased by 5 percent. To produce such a multilayer coating, TiO₂ is evaporated onto freshly deposited aluminum until the aluminum reflectance decreases to a minimum at λ=620 mµ. The direct evaporation of TiO₂ results in a slightly reduced, strongly absorbing film material (TiO_x). By anodic treatment in an electrolyte, such as 3 percent ammonium tartrate, the absorbing TiO_x on aluminum can be oxidized to nonabsorbing TiO₂, and part of the aluminum can be converted to Al₂O₃ underneath the TiO₂. Seventy-five volts must be applied to produce quarter-wavelength thick films of Al₂O₃ and TiO₂ at λ=530 mµ. Al₂O₃–TiO₂ coatings furnish better protection than the most frequently used MgF₂–ZnS film pairs. Two film pairs of Al₂O₃ and TiO₂ can also be applied in one anodic process.

© 1954 Optical Society of America

On the Preparation of Hard Oxide Films with Precisely Controlled Thickness on Evaporated Aluminum Mirrors*

Georg Hass
J. Opt. Soc. Am. 39(7) 532-540 (1949)

Optical Properties of Silicon Monoxide in the Wavelength Region from 0.24 to 14.0 Microns*

Georg Hass and Calvin D. Salzberg
J. Opt. Soc. Am. 44(3) 181-187 (1954)

Increasing the Far-Ultraviolet Reflectance of Silicon-Oxide-Protected Aluminum Mirrors by Ultraviolet Irradiation*

Alan P. Bradford and Georg Hass
J. Opt. Soc. Am. 53(9) 1096-1100 (1963)

On the Vacuum-Ultraviolet Reflectance of Evaporated Aluminum before and during Oxidation*

R. P. Madden, L. R. Canfield, and G. Hass
J. Opt. Soc. Am. 53(5) 620-625 (1963)

Infrared Reflectance of Evaporated Aluminum Films

H. E. Bennett, Jean M. Bennett, and E. J. Ashley
J. Opt. Soc. Am. 52(11) 1245-1250 (1962)