The Simons Observatory: Rotation Performance of Cryogenic Half-Wave Plate Polarization Modulators
Abstract
We present the on-site rotation performance of the first three cryogenic continuously rotating half-wave plate (HWP) polarization modulators for the Simons Observatory small aperture telescopes (SATs). The SATs operate at an altitude of 5200 m in the Atacama Desert in northern Chile, and measure the degree-scale cosmic microwave background polarization to search for primordial B-mode polarization. To this end, the SATs employ a 505 mm diameter 50 K cryogenic HWP polarization modulator to suppress atmospheric 1/f noise and to mitigate systematic uncertainties. We present methods for reconstructing the rotation of our polarization modulators, enabling detailed evaluations of their rotation angle accuracy, stability, displacements, and vibrations. We achieve the required rotation angle accuracy in more than 99.9% of observations, with a median noise level of 0.16 μrad√s. We also achieve one-dimensional measurement of the rotor displacement with an accuracy of 0.06 μm√s. Our results demonstrate the on-site rotation performance, rotation angle reconstruction method, and robustness of the polarization modulators. This is a crucial step towards achieving the SAT science goals.
Versions
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BibTeX
@misc{yamada2026simons,
title = {{The Simons Observatory: Rotation Performance of Cryogenic Half-Wave Plate Polarization Modulators}},
author = {Kyohei Yamada and Bryce Bixler and Junna Sugiyama and Daichi Sasaki and Yuki Sakurai and Kam Arnold and Samuel Day-Weiss and Nicholas Galitzki and Bradley R. Johnson and Akito Kusaka and Lyman A. Page and Yoshinori Sueno and Satoru Takakura},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.27056},
eprint = {2605.27056},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.27056},
}
RIS
TY - UNPB
TI - The Simons Observatory: Rotation Performance of Cryogenic Half-Wave Plate Polarization Modulators
AU - Kyohei Yamada
AU - Bryce Bixler
AU - Junna Sugiyama
AU - Daichi Sasaki
AU - Yuki Sakurai
AU - Kam Arnold
AU - Samuel Day-Weiss
AU - Nicholas Galitzki
AU - Bradley R. Johnson
AU - Akito Kusaka
AU - Lyman A. Page
AU - Yoshinori Sueno
AU - Satoru Takakura
PY - 2026
DA - 2026/09/23
PB - arXiv
DO - 10.48550/arxiv.2605.27056
UR - https://arxiv.org/abs/2605.27056
AB - We present the on-site rotation performance of the first three cryogenic continuously rotating half-wave plate (HWP) polarization modulators for the Simons Observatory small aperture telescopes (SATs). The SATs operate at an altitude of 5200 m in the Atacama Desert in northern Chile, and measure the degree-scale cosmic microwave background polarization to search for primordial B-mode polarization. To this end, the SATs employ a 505 mm diameter 50 K cryogenic HWP polarization modulator to suppress atmospheric 1/f noise and to mitigate systematic uncertainties. We present methods for reconstructing the rotation of our polarization modulators, enabling detailed evaluations of their rotation angle accuracy, stability, displacements, and vibrations. We achieve the required rotation angle accuracy in more than 99.9% of observations, with a median noise level of 0.16 μrad√s. We also achieve one-dimensional measurement of the rotor displacement with an accuracy of 0.06 μm√s. Our results demonstrate the on-site rotation performance, rotation angle reconstruction method, and robustness of the polarization modulators. This is a crucial step towards achieving the SAT science goals.
ER -