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Proceedings Paper

A cryogenic dichroic mirror for separating visible light from wideband infrared
Author(s): K. Enya; N. Fujishiro; K. Haze; T. Kotani; H. Kaneda; S. Oyabu; D. Ishihara; S. Oseki
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Paper Abstract

We present the design, fabrication and test results for a dichroic mirror, which was primarily developed for the SPICA Coronagraph Instrument (SCI), but is potentially useful for various types of astronomical instrument. The dichroic mirror is designed to reflect near- and mid-infrared but to transmit visible light. Two designs, one with 3 layers and one with 5 layers on BK7 glass substrates, are presented. The 3-layer design, consisting of Ag and ZnS, is simpler, and the 5-layer design, consisting of Ag and TiO2 is expected to have better performance. Tape tests, evaluation of the surface figure, and measurements of the reflectivity and transmittance were carried out at ambient temperature in air. The reflectivity obtained from measurements made on mirrors with 5 layers were < 80 % for wavelengths, λ, from 1.2 to 22 μm and < 90 % for λ from 1.8 to 20 μm. The transmittance obtained from measurements made on mirrors with 5 layers were < 70 % for λ between 0.4 and 0.8 μm. Optical ghosting is estimated to be smaller than 10-4 at λ < 1.5 μm. A protective coating for preventing corrosion was applied and its influence on the reflectivity and transmittance evaluated. A study examining the trade-offs imposed by various configurations for obtaining a telescope pointing correction signal was also undertaken.

Paper Details

Date Published: 2 August 2014
PDF: 8 pages
Proc. SPIE 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 91434J (2 August 2014); doi: 10.1117/12.2055807
Show Author Affiliations
K. Enya, Japan Aerospace Exploration Agency (Japan)
N. Fujishiro, Koyama Astronomical Observatory, Kyoto Sangyo Univ. (Japan)
K. Haze, Japan Aerospace Exploration Agency (Japan)
T. Kotani, National Astronomical Observatory of Japan (Japan)
H. Kaneda, Nagoya Univ. (Japan)
S. Oyabu, Nagoya Univ. (Japan)
D. Ishihara, Nagoya Univ. (Japan)
S. Oseki, Nagoya Univ. (Japan)


Published in SPIE Proceedings Vol. 9143:
Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave
Jacobus M. Oschmann; Mark Clampin; Giovanni G. Fazio; Howard A. MacEwen, Editor(s)

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