The reflectance of silver and gold evaporated in ultrahigh vacuum has been measured in the wavelength range from 0.5 µ to 32 µ. It was found that the reflectance of both materials is higher than previously reported values, and that ultrahigh vacuum silver films have the highest infrared reflectance over an extended wavelength range of any known material. The infrared emittance of uhv gold films is nearly as low as that of silver and is smaller by nearly a factor of 3 than the value previously reported for this material. Since gold is chemically inert and its emittance apparently does not change with time, it should find wider application as a low infrared emittance material, particularly in problems involving radiative heat transfer.
Jean M. Bennett and E. J. Ashley, "Infrared Reflectance and Emittance of Silver and Gold Evaporated in Ultrahigh Vacuum," Appl. Opt. 4, 221-224 (1965)