Intensity-Coupled-Polarization in Instruments with a Continuously Rotating Half-Wave Plate
astro-ph.IM
/ Authors
Joy Didier, Amber D. Miller, Derek Araujo, François Aubin, Christopher Geach, Bradley Johnson, Andrei Korotkov, Kate Raach, Benjamin Westbrook, Karl Young
and 24 more authors
Asad M. Aboobaker, Peter Ade, Carlo Baccigalupi, Chaoyun Bao, Daniel Chapman, Matt Dobbs, Will Grainger, Shaul Hanany, Kyle Helson, Seth Hillbrand, Johannes Hubmayr, Andrew Jaffe, Terry Jones, Jeff Klein, Adrian Lee, Michele Limon, Kevin MacDermid, Michael Milligan, Enzo Pascale, Britt Reichborn-Kjennerud, Ilan Sagiv, Carole Tucker, Gregory S. Tucker
/ Abstract
We discuss a systematic effect associated with measuring polarization with a continuously rotating half-wave plate. The effect was identified with the data from the E and B Experiment (EBEX), which was a balloon-borne instrument designed to measure the polarization of the CMB as well as that from Galactic dust. The data show polarization fraction larger than 10\% while less than 3\% were expected from instrumental polarization. We give evidence that the excess polarization is due to detector non-linearity in the presence of a continuously rotating HWP. The non-linearity couples intensity signals into polarization. We develop a map-based method to remove the excess polarization. Applying this method for the 150 (250) GHz bands data we find that 81\% (92\%) of the excess polarization was removed. Characterization and mitigation of this effect is important for future experiments aiming to measure the CMB B-modes with a continuously rotating HWP.