Variable-delay Polarization Modulators for Cryogenic Millimeter-wave   Applications
  We describe the design, construction, and initial validation of the variable-delay polarization modulator (VPM) designed for the PIPER cosmic microwave background polarimeter. The VPM modulates between linear and circular polarization by introducing a variable phase delay between orthogonal linear polarizations. Each VPM has a diameter of 39 cm and is engineered to operate in a cryogenic environment (1.5 K). We describe the mechanical design and performance of the kinematic double-blade flexure and drive mechanism along with the construction of the high precision wire grid polarizers. 
David T. Chuss, Joseph R. Eimer, Dale J. Fixsen, James Hinderks, Alan   J. Kogut, Justin Lazear, Paul Mirel, Eric Switzer, G...
astro-ph.IM