Intensity-coupled Polarization in Instruments with a Continuously Rotating Half-wave Plate

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https://iopscience.iop.org/article/10.3847/1538-4357/ab0f36/pdf

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https://doi.org/10.3847/1538-4357/ab0f36
 http://hdl.handle.net/11603/24141

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UMBC Center for Space Sciences and Technology (CSST) / Center for Research and Exploration in Space Sciences & Technology II (CRSST II)

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https://orcid.org/0000-0001-9238-4918

Date

2019-05-01

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journal articles
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Citation of Original Publication

Didier, 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.

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This 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.
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Abstract

We 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.