XXVI. Optical constants of metals in the infra-red—experimental methods

Abstract

Summary For metals the principal angle of incidence in the infra-red is near 90° and it has been shown that the real and imaginary parts of the dielectric constant are best obtained by measuring ρ and Δ; ρ is the ratio of the reflectivities of the p- and s- components and Δ the relative phase difference. ρ and Δ may be obtained without using birefringent materials by measuring two ratios of intensities, a technique which provides a cross-check. The experimental methods and arrangements developed to measure a number of metals in the spectral range 2μ to 12μ are described ; this range can be extended where necessary. Use of multiple reflections is discussed and errors are examined. Measurements are reported of evaporated aluminium mirrors since these are frequently used.