Anomalous Reflectivity Losses of Coated Mirrors Used in the Infrared

摘要

It has recently been found that front-surfaced aluminium mirrors coated with a variety of thin protective layers have severe reflectivity losses when used at non-normal angles of incidence between 8 and 12 micrometers. This memorandum gives the mechanism for this anomalous loss and derives the condition that the loss will occur if cos theta sub o < (N sub 1(2) + K sub 1(2))/1/2 where theta sub o is the angle of incidence. Three materials proposed to replace the conventional oxides of silicon as protective coatings, and the reflectivity losses of tarnished aluminium mirrors, are discussed in section 4. (Author)