Modulation of cosmic microwave background polarization with a warm rapidly rotating half-wave plate on the Atacama B-Mode Search instrument

Abstract

We evaluate the modulation of Cosmic Microwave Background (CMB) polarization using a rapidly-rotating, half-wave plate (HWP) on the Atacama B-Mode Search (ABS). After demodulating the time-ordered-data (TOD), we find a significant reduction of atmospheric fluctuations. The demodulated TOD is stable on time scales of 500-1000 seconds, corresponding to frequencies of 1-2 mHz. This facilitates recovery of cosmological information at large angular scales, which are typically available only from balloon-borne or satellite experiments. This technique also achieves a sensitive measurement of celestial polarization without differencing the TOD of paired detectors sensitive to two orthogonal linear polarizations. This is the first demonstration of the ability to remove atmospheric contamination at these levels from a ground-based platform using a rapidly-rotating HWP.

Characterization of the Atacama B-mode Search

“…The HWP has allowed for a low knee frequency of 2.0 mHz, enabling the recovery of large angular scales relevant to the primordial B-mode peak at 2 • . 20 The spectral responses of many of the detectors have been characterized in situ using an FTS, and future measurements are planned. The telescope pointing model is adequate and further improvements to the model are in progress.…”

“…The HWP modulation scheme suppresses 1/f noise, which arises primarily from the atmosphere but can also arise from focal plane temperature fluctuations and readout electronics. 20 The ABS HWP is the first optical element of the telescope, which also allows for the separation of instrumental polarization and signal polarization.…”

“…After demodulating the HWP, the median knee frequency of the detectors is 2.0 mHz, which allows for the recovery of information from large angular scales otherwise not easily available to ground-based instruments. 20 The detector time constants have been measured ( 3 ms) and are sufficiently fast to respond to the 10 Hz polarization modulation of the HWP. 23 …”

Recovery of Large Angular Scale CMB Polarization for Instruments Employing Variable-Delay Polarization Modulators

“…This is especially important in CMB polarization measurements for which the signal of interest is small, extended, and measured in the presence of large backgrounds. Detailed studies of the instrumental response have been previously carried out for a variety of system architectures (MacTavish et al 2008;Shimon et al 2008;Miller et al 2009;Karakci et al 2013;Kusaka et al 2014). This paper undertakes a similar analysis for a VPM-based polarimeter architecture.…”

“…System level implementations of polarization modulation employ such devices such as half-wave plates (HWP; Reichborn-Kjennerud et al 2010;Fraisse et al 2013;Kusaka et al 2014), Faraday rotators (Moyerman et al 2013), and phase switched receiver architectures (Jarosik et al 2003;Bersanelli et al 2010;QUIET Collaboration et al 2013) that vary the polarization state of the incoming radiation for synchronous demodulation and detection of the signal. In the ideal case, unpolarized and polarized components of the incoming radiation are treated independently by the system architecture and analysis pipeline.…”