Variable-delay Polarization Modulators for the CLASS Telescopes
Abstract
The search for inflationary primordial gravitational waves and the measurement of the optical depth to reionization, both through their imprint on the large angular scale correlations in the polarization of the cosmic microwave background (CMB), has created the need for high sensitivity measurements of polarization across large fractions of the sky at millimeter wavelengths. These measurements are subject to instrumental and atmospheric noise, which has motivated the development of polarization modulators to facilitate the rejection of these large systematic effects. Variable-delay polarization modulators (VPMs) are used in the Cosmology Large Angular Scale Surveyor (CLASS) telescopes as the first element in the optical chain to rapidly modulate the incoming polarization. VPMs consist of a linearly polarizing wire grid in front of a movable flat mirror. Varying the distance between the grid and the mirror produces a changing phase shift between polarization states parallel and perpendicular to the grid which modulates Stokes U (linear polarization at ) and Stokes V (circular polarization). The CLASS telescopes have VPMs as the first optical element from the sky; this simultaneously allows a lock-in style polarization measurement and the separation of sky polarization from any instrumental polarization further along in the optical path. The Q-band CLASS VPM was the first VPM to begin observing the CMB full time, starting in the Spring of 2016. The first W-band CLASS VPM was installed in the Spring of 2018.
Cite
@article{arxiv.1807.03807,
title = {Variable-delay Polarization Modulators for the CLASS Telescopes},
author = {Kathleen Harrington and Joseph Eimer and David T. Chuss and Matthew Petroff and Joseph Cleary and Martin DeGeorge and Theodore W. Grunberg and Aamir Ali and John W. Appel and Charles L. Bennett and Michael Brewer and Ricardo Bustos and Manwei Chan and Jullianna Couto and Sumit Dahal and Kevin Denis and Rolando Dünner and Thomas Essinger-Hileman and Pedro Fluxa and Mark Halpern and Gene Hilton and Gary F. Hinshaw and Johannes Hubmayr and Jeffrey Iuliano and John Karakla and Tobias Marriage and Jeffrey McMahon and Nathan J. Miller and Carolina Nuñez and Ivan L. Padilla and Gonzalo Palma and Lucas Parker and Bastian Pradenas Marquez and Rodrigo Reeves and Carl Reintsema and Karwan Rostem and Deniz Augusto Nunes Valle and Trevor Van Engelhoven and Bingjie Wang and Qinan Wang and Duncan Watts and Janet Weiland and Edward Wollack and Zhilei Xu and Ziang Yan and Lingzhen Zeng},
journal= {arXiv preprint arXiv:1807.03807},
year = {2018}
}