Mechanical strength and millimeter-wave transmission spectrum of stacked sapphire plates bonded by sodium silicate solution

Takayuki Toda, Hirokazu Ishino, Kunimoto Komatsu, Tomotake Matsumura, Yuki Sakurai, Nobuhiko Katayama

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract

A polarization modulator unit for a low-frequency telescope in LiteBIRD employs an achromatic half-wave plate (AHWP). It consists of five-layer a-cut sapphire plates, which are stacked based on a Pancharatnam recipe. In this way, the retardance of the AHWP is a half-wave over the bandwidth of 34-161 GHz. The diameter of a single sapphire plate is about 500mm and the thickness is about 5 mm. When a large diameter AHWP is used for a space mission, it is important for the AHWP to survive launch vibration. A preliminary study indicates that the five-layer-stacked HWP has a risk of breakage at the launch unless the 5 layers are glued together and mechanically treated as one disk. In this paper, we report our investigation using a sodium silicate solution which can bond between sapphire plates. This technique has been previously investigated as a candidate cryogenic glue for a mirror material, including sapphire, of the gravitational wave detector, LIGO and KAGRA. We experimentally studied the mechanical strength of the bonded interface for two different surface conditions, polished and unpolished. We demonstrated the tensile and shear strength of above 20MPa for samples with a polished surface, respectively. We also identified that samples glued on a polished surface show higher strength than unpolished ones by a factor of 2 for tensile and 18 for shear strength. We searched for any optical effects, e.g. extra gap or absorption by the bonding interface, by measuring the millimeter-wave transmission spectra in 90-140 GHz. We did not find any optical effect caused by the bonded interface within 2% error in transmittance that is originated from the measurement system.

Original languageEnglish
Title of host publicationMillimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X
EditorsJonas Zmuidzinas, Jian-Rong Gao
PublisherSPIE
ISBN (Electronic)9781510636934
DOIs
Publication statusPublished - 2020
EventMillimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X 2020 - Virtual, Online, United States
Duration: Dec 14 2020Dec 22 2020

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
Volume11453
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X

Conference

ConferenceMillimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy X 2020
CountryUnited States
CityVirtual, Online
Period12/14/2012/22/20

Keywords

  • achromatic half-wave plate
  • mechanical strength
  • millimeter wave transmission
  • polarization modulator
  • sodium silicate bonding solution

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering

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