Optical Constants of Incandescent Refractory Metals

Abstract

Filaments of semicircular cross section (diam 0.25–0.32 mm) were mounted in bulbs with plane windows. Chopped plane-polarized radiant flux was reflected from the flat surface, then passed through an analyzer whose plane of polarization made a 45° angle with the plane of reflection at the filament. The orientation of the polarizer was varied in 45° steps, and wavelengths from 0.47 to 2.0 μ were used. The metals studied were W, Mo, Ta, Ir, Re, Nb, and Pt. Filament temperatures ranged from 300 to 2400–2500°K. (Maximum for Pt was 1900°.) n-vs-λ curves for different temperatures were close together in the visible, but spread apart with increasing wavelength in the infrared. Curves showing k vs λ and e vs λ usually crossed one another near a common point. Deviations from previously published data ranged up to 15 or 20%. Systematic errors in some of the infrared data, due to difficulty in centering the reflecting surface in the beam from the source lamp, are quite obvious. Rough agreement with a simplified form of the Drude theory is approached with increasing wavelength in certain cases.