19 July 2016 Design and development of an ambient-temperature continuously-rotating achromatic half-wave plate for CMB polarization modulation on the POLARBEAR-2 experiment
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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 ~ 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.
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Charles A. Hill, Charles A. Hill, Shawn Beckman, Shawn Beckman, Yuji Chinone, Yuji Chinone, Neil Goeckner-Wald, Neil Goeckner-Wald, Masashi Hazumi, Masashi Hazumi, Brian Keating, Brian Keating, Akito Kusaka, Akito Kusaka, Adrian T. Lee, Adrian T. Lee, Frederick Matsuda, Frederick Matsuda, Richard Plambeck, Richard Plambeck, Aritoki Suzuki, Aritoki Suzuki, Satoru Takakura, Satoru Takakura, "Design and development of an ambient-temperature continuously-rotating achromatic half-wave plate for CMB polarization modulation on the POLARBEAR-2 experiment", Proc. SPIE 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII, 99142U (19 July 2016); doi: 10.1117/12.2232280; https://doi.org/10.1117/12.2232280
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