HN22 sheet polarizer, an inexpensive infrared retarder

The popular sheet polarizer, Polaroid HN22, has been measured to be a nearly half-wave retarder in the 3.6–5.4-μm spectral band with a transmittance of approximately 20%. Tuning of the retardance value between 60° and 260° has been demonstrated by tilting of the HN22 sheet with respect to the incident beam. The material’s availability, relatively large aperture, large field of view, and low cost make it an excellent candidate for use as an infrared retarder for systems operating in this wave band. Thus HN22 may be employed as an inexpensive half-wave linear retarder and used for rotating the plane of polarization as well as for conversion between circular polarization states.