The Optical Constants of Silver, Gold, Copper, and Aluminum I The Absorption Coefficient k

Abstract

A description is given of a comparison method for determining the values of the absorption coefficient k of a metal relative to previously determined values for Ag. In this method transmission interference filters are constructed which have mica as the dielectric and have reflecting layers of Ag and of the metal x being studied. On adjacent areas of a single sheet of mica, pairs of filters are formed, one with a Ag-mica-Ag combination and the other with a Ag-mica-x combination. Components of a filter pair will have identical mica thicknesses. For a given filter pair the wavelengths transmitted by one combination are compared with those transmitted by the other. Values of k are then calculated from the change in phase accompanying the reflection of light at normal incidence at mica-metal interfaces. The method was found to have special advantages in the wavelength region of 0.65μ to 0.95μ for metals with high reflectivities. Results are given for Au, Cu, and Al in the range of 0.45μ to 0.95μ. The new values of k tend to be higher than older values obtained by other methods. A discussion is included concerning the validity of surface measurements for determining the bulk properties of metals.