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Proceedings Paper

Variable-delay polarization modulators for the CLASS telescopes
Author(s): Kathleen Harrington; Joseph Eimer; David T. Chuss; Matthew Petroff; Joseph Cleary; Martin DeGeorge; Theodore W. Grunberg; Aamir Ali; John W. Appel; Charles L. Bennett; Michael Brewer; Ricardo Bustos; Manwei Chan; Jullianna Couto; Sumit Dahal; Kevin Denis; Rolando Dünner; Thomas Essinger-Hileman; Pedro Fluxa; Mark Halpern; Gene Hilton; Gary F. Hinshaw; Johannes Hubmayr; Jeffrey Iuliano; John Karakla; Tobias Marriage; Jeffrey McMahon; Nathan J. Miller; Carolina Nuñez; Ivan L. Padilla; Gonzalo Palma; Lucas Parker; Bastian Pradenas Marquez; Rodrigo Reeves; Carl Reintsema; Karwan Rostem; Deniz Augusto Nunes Valle; Trevor Van Engelhoven; Bingjie Wang; Qinan Wang; Duncan Watts; Janet Weiland; Edward Wollack; Zhilei Xu; Ziang Yan; Lingzhen Zeng
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Paper 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 1=f 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 45°) 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 CLASS VPM wire grids use 50 μm copper-plated tungsten wire with a 160μm spacing across a 60 cm clear aperture. The mirror is mounted on a flexure system with one degree of translational freedom, enabling the required mirror motion while maintaining excellent parallelism with respect to the wire grid. The wire grids and mirrors are held parallel to each other to better than 80 μm, and the wire grids have RMS flatness errors below 50 μm across the 60 cm aperture. 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.

Paper Details

Date Published: 9 July 2018
PDF: 22 pages
Proc. SPIE 10708, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX, 107082M (9 July 2018); doi: 10.1117/12.2313614
Show Author Affiliations
Kathleen Harrington, Johns Hopkins Univ. (United States)
Joseph Eimer, Johns Hopkins Univ. (United States)
David T. Chuss, Villanova Univ. (United States)
Matthew Petroff, Johns Hopkins Univ. (United States)
Joseph Cleary, Johns Hopkins Univ. (United States)
Martin DeGeorge, Villanova Univ. (United States)
Theodore W. Grunberg, Johns Hopkins Univ. (United States)
Massachusetts Institute of Technology (United States)
Aamir Ali, Johns Hopkins Univ. (United States)
Univ. of California, Berkeley (United States)
John W. Appel, Johns Hopkins Univ. (United States)
Charles L. Bennett, Johns Hopkins Univ. (United States)
Michael Brewer, Johns Hopkins Univ. (United States)
Ricardo Bustos, Univ. Católica de la Santísima Concepción (Chile)
Manwei Chan, Johns Hopkins Univ. (United States)
Jullianna Couto, Johns Hopkins Univ. (United States)
Sumit Dahal, Johns Hopkins Univ. (United States)
Kevin Denis, NASA Goddard Space Flight Ctr. (United States)
Rolando Dünner, Pontificia Univ. Católica de Chile (Chile)
Thomas Essinger-Hileman, NASA Goddard Space Flight Ctr. (United States)
Pedro Fluxa, Pontificia Univ. Católica de Chile (Chile)
Mark Halpern, The Univ. of British Columbia (Canada)
Gene Hilton, National Institute of Standards and Technology (United States)
Gary F. Hinshaw, The Univ. of British Columbia (Canada)
Johannes Hubmayr, National Institute of Standards and Technology (United States)
Jeffrey Iuliano, Johns Hopkins Univ. (United States)
John Karakla, Johns Hopkins Univ. (United States)
Tobias Marriage, Johns Hopkins Univ. (United States)
Jeffrey McMahon, Univ. of Michigan (United States)
Nathan J. Miller, Johns Hopkins Univ. (United States)
Carolina Nuñez, Johns Hopkins Univ. (United States)
Ivan L. Padilla, Johns Hopkins Univ. (United States)
Gonzalo Palma, Univ. de Chile (Chile)
Lucas Parker, Johns Hopkins Univ. (United States)
Los Alamos National Lab. (United States)
Bastian Pradenas Marquez, Univ. de Chile (Chile)
Rodrigo Reeves, Univ. de Concepción (Chile)
Carl Reintsema, National Institute of Standards and Technology (United States)
Karwan Rostem, NASA Goddard Space Flight Ctr. (United States)
Deniz Augusto Nunes Valle, Johns Hopkins Univ. (United States)
Trevor Van Engelhoven, Johns Hopkins Univ. (United States)
Bingjie Wang, Johns Hopkins Univ. (United States)
Qinan Wang, Johns Hopkins Univ. (United States)
Duncan Watts, Johns Hopkins Univ. (United States)
Janet Weiland, Johns Hopkins Univ. (United States)
Edward Wollack, NASA Goddard Space Flight Ctr. (United States)
Zhilei Xu, Johns Hopkins Univ. (United States)
Univ. of Pennsylvania (United States)
Ziang Yan, The Univ. of British Columbia (Canada)
Lingzhen Zeng, Harvard-Smithsonian Ctr. for Astrophysics (United States)


Published in SPIE Proceedings Vol. 10708:
Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy IX
Jonas Zmuidzinas; Jian-Rong Gao, Editor(s)

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