Experimental data are presented for the normal spectral absorptivities of the transition metals, nickel, iron, platinum, and chromium at both room and liquid-helium temperatures in the wavelength range 2.5–50 μm. The absorptivities were derived from reflectivity measurements made relative to a room-temperature vapor-deposited gold reference mirror. The absorptivity of the gold reference mirror was measured calorimetrically, by use of infrared laser sources. Investigation of various methods of sample-surface preparation resulted in the choice of a vacuum-annealing process as the final stage. The experimental results are discussed on the basis of the anomalous-skin-effect theory modified for multiple conduction bands. As predicted, the results approach a single-band model towards the longer wavelengths. Agreement between theory and experiment is considerably improved by taking into account the modification of the relaxation time due to the photon–electron–phonon interaction proposed by Holstein and Gurzhi; but, particularly at helium temperatures, the calculated curve is consistently below the experimental results.
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