Optical Properties of Copper

Optical properties of solid copper have been measured in a wavelength range from 0.365 to 2.5 microns and at temperatures 90°, 300°, and 500°K. Annealed and electropolished specimens were used. Measurements were done in a vacuum of about 2×${10}^{-5\mathrm{}}$ mm (Hg) and it was observed that the oxide film which normally forms on copper upon exposure to air could be removed by heating in vacuum to a temperature of 500°K. In the wavelength range below 0.6 micron the data confirm the well-known facts relating to a threshold for interband electronic transitions. At longer wavelengths the optical properties are determined almost entirely by free electrons. Deviations from simple theory are partly explained by the anomalous skin effect and it is concluded that the electronic collisions at the metal surface are diffuse. However, it is shown that the anomalous skin effect is not sufficient to explain the observed deviations and that a more complete interpretation ought to consider the nonspherical nature of the Fermi surface and variation of the relaxation time over this surface.