Optical Properties of Tellurium in the Infra-Red

The refractive index and absorption constant of tellurium layers have been measured in the near infra-red. The refractive index has been measured over the wavelength range 3 μ to 11 μ. The value extrapolated to long wavelengths is found to be 4.8; this is much higher than any other known refractive index. Absorption measurements were made for wavelengths 1 μ to 3 μ: the absorption constant is 2.2 × 105 cm-1 at 1.0 μ, falling rapidly with increasing wavelength. Transmission measurements on bulk specimens are possible at wavelengths greater than 3.3 μ.