An infra-red reflectometer with a spheroidal mirror

The design and performance are discussed of an infra-red reflectometer in which a spheroidal mirror focuses the reflected radiation on a bolometer. Spectral reflectance curves over the wavelength range 0.7-14 μm are given for several materials, and it is shown that the reflectometer can be used to measure the angular distribution of reflected radiation. Systematic errors are much lower than those obtained with the Coblentz hemisphere, and rarely exceed 0.02 of the reflectance values. The Gier-Dunkle cavity gives similar accuracy, but the present instrument is preferable for samples which are poor thermal conductors.