Mathematics – Logic
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012aas...21942228b&link_type=abstract
American Astronomical Society, AAS Meeting #219, #422.28
Mathematics
Logic
Scientific paper
The Keck Array, a set of 5 microwave polarimeters located at the South Pole, is currently looking for the imprint of inflationary gravitational waves as B-mode polarization in the CMB. In order for the Keck Array to reach its sensitivity goal, the polarization orientation for each detector must be known to 0.1 degree precision and the polarization efficiency must be known to 0.5% precision. To perform this detector calibration, we designed and constructed a rotating polarized microwave source that can generate broadband radiation covering 100, 150 or 220 GHz bands, the observing frequencies of the Keck Array, in a broad beam with a precisely defined linear polarization and less than 0.5% cross-polar power. The source is capable of rotating a full 360 degrees and the absolute orientation angle of the source is known to <0.1 degrees. The source is affixed to a rotary stage with a stepper motor, and a high degree of linear polarization is achieved with a free-standing wire grid polarizer. The absolute orientation of the source is referenced to gravity using a built-in tilt meter. This new source allows the polarization response of each of the Keck Array's detectors to be measured, without which strong E-mode polarizations would appear as false B-mode patterns. Such false patterns would contaminate any real B-mode polarization signal or could be mistaken for cosmological birefringence.
Bradford Kristi J.
Keck Array Team
Kovac John M.
Vieregg A. G.
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