Concept Design of Low Frequency Telescope for CMB B-mode Polarization satellite LiteBIRD

Abstract

LiteBIRD has been selected as JAXA's strategic large mission in the 2020s, to observe the cosmic microwave background (CMB) $B$-mode polarization over the full sky at large angular scales. The challenges of LiteBIRD are the wide field-of-view (FoV) and broadband capabilities of millimeter-wave polarization measurements, which are derived from the system requirements. The possible paths of stray light increase with a wider FoV and the far sidelobe knowledge of $-56$ dB is a challenging optical requirement. A crossed-Dragone configuration was chosen for the low frequency telescope (LFT : 34--161 GHz), one of LiteBIRD's onboard telescopes. It has a wide field-of-view ($18^{\circ }\times 9^{\circ }$) with an aperture of 400 mm in diameter, corresponding to an angular resolution of about 30 arcminutes around 100 GHz. The focal ratio f/3.0 and the crossing angle of the optical axes of 90${}^{\circ }$ are chosen after an extensive study of the stray light. The primary and secondary reflectors have rectangular shapes with serrations to reduce the diffraction pattern from the edges of the mirrors. The reflectors and structure are made of aluminum to proportionally contract from warm down to the operating temperature at $5$K. A 1/4 scaled model of the LFT has been developed to validate the wide field-of-view design and to demonstrate the reduced far sidelobes. A polarization modulation unit (PMU), realized with a half-wave plate (HWP) is placed in front of the aperture stop, the entrance pupil of this system. A large focal plane with approximately 1000 AlMn TES detectors and frequency multiplexing SQUID amplifiers is cooled to 100 mK. The lens and sinuous antennas have broadband capability. Performance specifications of the LFT and an outline of the proposed verification plan are presented.

arXiv comment21 pages, 14 figures

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• The Quest for B Modes from Inflationary Gravitational Waves
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Cited by in corpus (7)

• Cosmic birefringence tomography and calibration-independence with reionization signals in the CMB
• In-flight polarization angle calibration for LiteBIRD: blind challenge and cosmological implications
• Planar near-field measurements of specular and diffuse reflection of millimeter-wave absorbers
• Optimization procedure of the baffle of the GroundBIRD Telescope to mitigate stray light
• Modified crossed Dragone optical design of the LiteBIRD low-frequency telescope
• Non-Gaussianity from explicit $U(1)$-breaking interactions
• On the computational feasibility of Bayesian end-to-end analysis of LiteBIRD simulations within Cosmoglobe