Design and development of an ambient-temperature continuously-rotating achromatic half-wave plate for CMB polarization modulation on the POLARBEAR-2 experiment

Abstract

We describe the development of an ambient-temperature continuously-rotating half-wave plate (HWP) for study of the Cosmic Microwave Background (CMB) polarization by the POLARBEAR-2 (PB2) experiment. Rapid polarization modulation suppresses 1/f noise due to unpolarized atmospheric turbulence and improves sensitivity to degree-angular-scale CMB fluctuations where the inflationary gravitational wave signal is thought to exist. A HWP modulator rotates the input polarization signal and therefore allows a single polarimeter to measure both linear polarization states, eliminating systematic errors associated with differencing of orthogonal detectors. PB2 projects a 365-mm-diameter focal plane of 7,588 dichroic, 95/150 GHz transition-edge-sensor bolometers onto a 4-degree field of view that scans the sky at $\sim$ 1 degree per second. We find that a 500-mm-diameter ambient-temperature sapphire achromatic HWP rotating at 2 Hz is a suitable polarization modulator for PB2. We present the design considerations for the PB2 HWP, the construction of the HWP optical stack and rotation mechanism, and the performance of the fully-assembled HWP instrument. We conclude with a discussion of HWP polarization modulation for future Simons Array receivers.

arXiv commentTo be published in Proc. of SPIE, Volume 9914, Number 99142U-1, 2016

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• A Large-Diameter Hollow-Shaft Cryogenic Motor Based on a Superconducting Magnetic Bearing for Millimeter-Wave Polarimetry
• Improved upper limit on degree-scale CMB B-mode polarization power from the 670 square-degree POLARBEAR survey
• A cryogenic continuously rotating half-wave plate for the POLARBEAR-2b cosmic microwave background receiver
• Measurements of tropospheric ice clouds with a ground-based CMB polarization experiment, POLARBEAR
• Impact of half-wave plate systematics on the measurement of cosmic birefringence from CMB polarization
• Systematic effects induced by Half Wave Plate precession into Cosmic Microwave Background polarization measurements
• The Simons Observatory: Development and Optical Evaluation of Achromatic Half-Wave Plates
• Impact of half-wave plate systematics on the measurement of CMB $B$-mode polarization
• Optimal strategy for polarization modulation in the LSPE-SWIPE experiment
• Anti-reflection coating with mullite and Duroid for large-diameter cryogenic sapphire and alumina optics
• Characterization of a half-wave plate for cosmic microwave background circular polarization measurement with POLARBEAR
• Modeling optical systematics for the Taurus CMB experiment
• A measurement of atmospheric circular polarization with POLARBEAR
• Systematic effects on lensing reconstruction from a patchwork of CMB polarization maps
• The Simons Observatory: Quantifying the impact of beam chromaticity on large-scale B-mode science
• Calibration of detector time constant with a thermal source for the POLARBEAR-2A CMB polarization experiment