The percent polarization for the infrared radiation reflected from a germanium mirror hag been measured to be greater than 99% from the near to far infrared wavelength regions. The intensity of the polarized beam was about 40% of that of the original unpolarized beam. The advantages of the germanium polarizer are the constant high degree of polarization over the wide wavelength region, the availability and ease of preparation of the mirror, ruggedness, and the polarizing properties which do not change with age or when exposed to intense radiation.
DAVID F. EDWARDS and MARTHA J. BRUEMMER, "Polarization of Infrared Radiation by Reflection from Germanium Surfaces," J. Opt. Soc. Am. 49, 860-861 (1959)