Author list: Ryota Takaku, Tommaso Ghigna, Shaul Hanany, Yurika Hoshino, Hirokazu Ishino, Nobuhiko Katayama, Kunimoto Komatsu, Kuniaki Konishi, Makoto Kuwata-Gonokami, Tomotake Matsumura, Haruyuki Sakurai, Yuki Sakurai, Qi Wen, Noriko Y. Yamasaki and Yumoto Junji for the LiteBIRD collaboration
Journal: Journal of Low Temperature Physics, Volume 211, pages 346–356, (2023) JLTP
Abstract: We laser-ablated sub-wavelength structures (SWS) on 200 mm diameter birefringent sapphire disks to produce broadband anti-reflection coating (ARC). The disks were assembled into a stack of five plates making an achromatic half-wave plate (AHWP) suitable for operation between 40 and 140 GHz. We report on the SWS fabrication and transmission measurements of the stack at room temperature. From the measurements, we compute a band average transmission and modulation efficiency for nine spectral bands that correspond to the frequency coverage of the LiteBIRD Low-Frequency Telescope (LFT). We also assess the level of instrumental polarization the AHWP exhibits. We discuss paths for further development to minimize the instrumental polarization from the AHWP. This work is a development milestone toward the implementation of an AHWP for the LiteBIRD satellite.
