Didier, JoyMiller, Amber D.Araujo, DerekAubin, FrançoisHelson, Kyleet al2022-02-082022-02-082019-05-01Didier, Joy et al. Intensity-coupled Polarization in Instruments with a Continuously Rotating Half-wave Plate. The Astrophysical Journal, 876 (May 3, 2019) 1. https://doi.org/10.3847/1538-4357/ab0f36.https://doi.org/10.3847/1538-4357/ab0f36http://hdl.handle.net/11603/24141Authors: Joy Didier, , Amber D. Miller, , Derek Araujo , François Aubin, , Christopher Geach , Bradley Johnson , Andrei Korotkov , Kate Raach , Benjamin Westbrook , Karl Young , 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 J. Jones , Jeff Klein , Adrian Lee , Michele Limon, , Kevin MacDermid , Michael Milligan , Enzo Pascale, Britt Reichborn-Kjennerud , Ilan Sagiv , Carole Tucker , Gregory S. Tucker , and Kyle ZilicWe discuss a systematic effect associated with measuring polarization with a continuously rotating half-wave plate (HWP). The effect was identified with the data from the E and B Experiment, which was a balloon-borne instrument designed to measure the polarization of the cosmic microwave background (CMB) as well as that from Galactic dust. The data show polarization fractions larger than 10%, while less than 3% were expected from instrumental polarization. We give evidence that the excess polarization is due to detector nonlinearity in the presence of a continuously rotating HWP. The nonlinearity couples intensity signals to polarization. We develop a map-based method to remove the excess polarization. Applying this method to the 150 (250) GHz band data, we find that 81% (92%) of the excess polarization was removed. Characterization and mitigation of this effect are important for future experiments aiming to measure the CMB B-modes with a continuously rotating HWP.14 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domain Mark 1.0Text