Characterizing Atacama B-mode Search Detectors with a Half-Wave Plate
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The Atacama B-Mode Search (ABS) instrument is a cryogenic (\(\sim \)10 K) crossed-Dragone telescope located at an elevation of 5190 m in the Atacama Desert in Chile that observed for three seasons between February 2012 and October 2014. ABS observed the cosmic microwave background (CMB) at large angular scales (\(40<\ell <500\)) to limit the B-mode polarization spectrum around the primordial B-mode peak from inflationary gravity waves at \(\ell \sim 100\). The ABS focal plane consists of 480 transition-edge sensor (TES) bolometers. They are coupled to orthogonal polarizations from a planar ortho-mode transducer and observe at 145 GHz. ABS employs an ambient-temperature, rapidly rotating half-wave plate (HWP) to mitigate systematic effects and move the signal band away from atmospheric 1 / f noise, allowing for the recovery of large angular scales. We discuss how the signal at the second harmonic of the HWP rotation frequency can be used for data selection and for monitoring the detector responsivities.
KeywordsAtacama B-mode Search Cosmic microwave background Polarization Half-wave plate
This work is supported by a NASA Space Technology Research Fellowship. Work at NIST is supported by the NIST Innovations in Measurement Science Program. Work at Princeton University is supported by the NSF through Awards PHY-0355328 and PHY-085587, NASA through award NNX08AE03G, and Wilkinson Misrahi funds. PWV measurements were provided by APEX. SR acknowledges his CONICYT Ph.D. studentship, CONICYT Anillo Project (ACT No. 1122), and the Aspen Center for Physics, which is supported by National Science Foundation Grant PHY-1066293. A. K. was supported by a Dicke Fellowship. This work was supported in part by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231.