In-line quarter-wave retarders for the infrared using total refraction and total internal reflection in a prism

Abstract

IR reflection quarter-wave retarders (QWR5) are described that maintain the collinearity of the transmitted and incident beams. One QWR uses a symmetric prism of Ge (refractive index n = 4) with an apex angle of 119 deg. Light incident parallel to the base of the prism is totally refracted, without change of polarization, at the side faces of the prism that are coated with an appropriate transparent bilayer. Total internal reflection at the prism base produces the desired 90-deg retardance. The second QWR uses a right-angle Ge prism with its base coated with a PbTe layer ( n = 5.1) to introduce the required phase shift at a 55.18-deg angle of incidence. The entrance and exit faces are antireflection coated with a polarization-preserving bilayer. Both QWRs are reasonably insensitive to small (±8 deg) angle-of-incidence errors.