Sidelobe optical simulations of the LiteBIRD low-frequency telescope and payload module

Frederick Matsuda; Ryo Nagata; Kimihide Odagiri; Shugo Oguri; Yutaro Sekimoto; Hayato Takakura; Tommaso Ghigna

doi:10.1117/12.3018635

23 August 2024 Sidelobe optical simulations of the LiteBIRD low-frequency telescope and payload module

Frederick Matsuda, Ryo Nagata, Kimihide Odagiri, Shugo Oguri, Yutaro Sekimoto, Hayato Takakura, Tommaso Ghigna

Proceedings Volume 13092, Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave; 1309229 (2024) https://doi.org/10.1117/12.3018635
Event: SPIE Astronomical Telescopes + Instrumentation, 2024, Yokohama, Japan

Abstract

LiteBIRD is a JAXA-led international project aimed to make high sensitivity measurements of the primordial B modes through cosmic microwave background (CMB) polarization observations. The Low-Frequency Telescope (LFT) is a modified crossed Dragone reflective telescope with a 18° × 9° field-of-view across the 34-161 GHz. To achieve the required observational sensitivity, the telescope’s sidelobe response must be characterized to high precision to minimize signal contamination systematic effects from galactic and foreground emission. We report on the development of LFT optical simulation models that include the reflector optics, optimized serrations, finite absorptivity baffling, and V-grooves, and characterize the LFT sidelobes accounting for multiple reflection and diffraction optical effects. We find that the implementation of triangular and cos² shaped serrations on the primary and secondary reflectors are effective in reducing asymmetric sidelobe power fluctuations to ≤ 1.42×10−4 and ≤ 1.20 × 10⁻⁴, respectively, at 34 GHz at 5.5° ≤ θbeam ≤ 35° from the beam center. Without telescope baffling, the LFT optics show prominent direct sidelobe and diffuse triple reflection sidelobes with peak powers of ≤ −35.49 dB and ≤ −38.65 dB, respectively. It was found that implementing a finite absorptivity focal plane (FP) hood and forebaffle allows for effectively mitigating these sidelobes to ≤ −58.66 dB at 34 and 42 GHz for θ > 45° from boresight. Further including V-grooves in the optical simulation model, it was found that the V-grooves attenuate the far sidelobe power at El < −50° to ≤ −74.8 dB. All these far-sidelobe features are found to be below the LiteBIRD sidelobe knowledge requirement levels.

Conference Presentation

(2024) Published by SPIE. Downloading of the abstract is permitted for personal use only.

Citation Download Citation

Frederick Matsuda, Ryo Nagata, Kimihide Odagiri, Shugo Oguri, Yutaro Sekimoto, Hayato Takakura, and Tommaso Ghigna "Sidelobe optical simulations of the LiteBIRD low-frequency telescope and payload module", Proc. SPIE 13092, Space Telescopes and Instrumentation 2024: Optical, Infrared, and Millimeter Wave, 1309229 (23 August 2024); https://doi.org/10.1117/12.3018635

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