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Published July 20, 2016 | Published
Book Section - Chapter Open

Optical characterization of the BICEP3 CMB polarimeter at the South Pole


BICEP3 is a small-aperture refracting cosmic microwave background (CMB) telescope designed to make sensitive polarization maps in pursuit of a potential B-mode signal from inflationary gravitational waves. It is the latest in the Bicep/Keck Array series of CMB experiments located at the South Pole, which has provided the most stringent constraints on inflation to date. For the 2016 observing season, BICEP3 was outfitted with a full suite of 2400 optically coupled detectors operating at 95 GHz. In these proceedings we report on the far field beam performance using calibration data taken during the 2015-2016 summer deployment season in situ with a thermal chopped source. We generate high-fidelity per-detector beam maps, show the array-averaged beam profile, and characterize the differential beam response between co-located, orthogonally polarized detectors which contributes to the leading instrumental systematic in pair differencing experiments. We find that the levels of differential pointing, beamwidth, and ellipticity are similar to or lower than those measured for Bicep2 and Keck Array. The magnitude and distribution of Bicep3's differential beam mismatch – and the level to which temperature-to-polarization leakage may be marginalized over or subtracted in analysis - will inform the design of next-generation CMB experiments with many thousands of detectors.

Additional Information

© 2016 Society of Photo-Optical Instrumentation Engineers (SPIE). The Bicep3 project has been made possible through support from the National Science Foundation (grant Nos. 1313158, 1313010, 1313062, 1313287, 1056465, and 0960243), the SLAC Laboratory Directed Research and Development Fund, the Canada Foundation for Innovation, and the British Columbia Development Fund. The development of antenna-coupled detector technology was supported by the JPL Research and Technology Development Fund and grants 06-ARPA206-0040 and 10-SAT10-0017 from the NASA ARPA and SAT programs. The development and testing of focal planes were supported by the Gordon and Betty Moore Foundation at Caltech. The computations in these proceedings were run on the Odyssey cluster supported by the FAS Science Division Research Computing Group at Harvard University. Tireless administrative support was provided by Irene Coyle, Kathy Deniston, Donna Hernandez, and Dana Volponi. We are grateful to Samuel Harrison and Hans Boenish as our 2015 and 2016 winterovers, espectively. We thank the staff of the US Antarctic Program and in particular the South Pole Station without whose help this research would not have been possible. We thank our Bicep1, Bicep2, Keck Array and Spider colleagues for useful discussions and shared expertise.

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