Characterization of sensitivity and responses of a 2-element prototype wavefront sensor for millimeter-wave adaptive optics attached to the Nobeyama 45m Telescope

Satoya Nakano; Yoichi Tamura; Akio Taniguchi; Sachiko Okumura; Ryohei Kawabe; Nozomi Okada; Tomoko Nakamura; Yuhei Fukasaku

doi:10.1117/12.2628269

29 August 2022 Characterization of sensitivity and responses of a 2-element prototype wavefront sensor for millimeter-wave adaptive optics attached to the Nobeyama 45m Telescope

Satoya Nakano, Yoichi Tamura, Akio Taniguchi, Sachiko Okumura, Ryohei Kawabe, Nozomi Okada, Tomoko Nakamura, Yuhei Fukasaku

Author Affiliations +

Proceedings Volume 12185, Adaptive Optics Systems VIII; 121856Z (2022) https://doi.org/10.1117/12.2628269
Event: SPIE Astronomical Telescopes + Instrumentation, 2022, Montréal, Québec, Canada

Conference Poster

Abstract

We report the results of the performance characterization of a prototype wavefront sensor for millimetric adaptive optics (MAO) installed on the Nobeyama 45 m radio telescope. MAO is a key component to realize a future large-aperture submillimeter telescope, such as Large Submillimeter Telescope (LST) or Atacama Large Aperture Submillimeter Telescope (AtLAST). The difficulty of MAO is, however, real-time sensing of wavefront deformation with ∼10 µm accuracy across the aperture. Our wavefront sensor operating at 20 GHz measures the radio path length between a certain position of the primary mirror surface to the focal point where a 20 GHz coherent receiver is placed. With the 2-element prototype, we sampled two positions on the primary mirror surface (at radii of 5 m and 16 m) at a sampling rate of 10 Hz. Then an excess path length (EPL) between the two positions was obtained by differentiating the two optical paths. A power spectral density of the EPL shows three components: a low-frequency drift (1/fⁿ), oscillations, and a white noise. A comparison of EPL measurements under a variety of wind conditions suggests that the former two are likely induced by the wind load on the telescope structure. The power of the white noise corresponds to a 1σ statistical error of 8 µm in EPL measurements. The 8 µm r.m.s. is significant with respect to the mirror surface accuracy required by the LST and AtLAST (∼20–40 µm r.m.s.), which demonstrates that our technique is also useful for the future large-aperture submillimeter telescopes.

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Satoya Nakano, Yoichi Tamura, Akio Taniguchi, Sachiko Okumura, Ryohei Kawabe, Nozomi Okada, Tomoko Nakamura, and Yuhei Fukasaku "Characterization of sensitivity and responses of a 2-element prototype wavefront sensor for millimeter-wave adaptive optics attached to the Nobeyama 45m Telescope", Proc. SPIE 12185, Adaptive Optics Systems VIII, 121856Z (29 August 2022); https://doi.org/10.1117/12.2628269

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