Universal ultrahigh vacuum facility for the measurement of the optical properties of solids.

An apparatus is described in which the reflectance and transmittance of a hot sample and a cold sample may be measured simultaneously and differentially in the wavelength region from the infrared to the vacuum ultraviolet. These measurements may be carried out under an ultrahigh vacuum or a gaseous ambience, and the surfaces may be temperature treated (e.g., flashed atomically clean) before the measurement. The hotcold differential capability of the apparatus is convenient when considering the temperature dependence of optical parameters.