Infra-Red Absorption by Metals at Low Temperatures

The infra-red absorptivities of several electropolished metal surfaces have been measured at liquid helium temperatures with a specially designed radiation cryostat with a black body at room temperature as the source and a differential helium gas thermometer as the detector It is found that the absorptivity of tin at 1.95° K for the mean estimated wavelength 14 μ remains the same in the normal and superconducting states to within a probable error of 0.3% The absorptivities of the normal metals, which include a number of alloys, are compared with the values calculated by various theories of metallic reflection. The classical Hagen-Rubens formula is found to be valid for the alloys except where there are complications such as the internal photoelectric effect The absorptivities of the pure metals are in fair agreement with the values calculated by the anomalous skin effect theory neglecting relaxation effects