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Proceedings Paper

The Infrared Imaging Spectrograph (IRIS) for TMT: optical design of IRIS imager with "co-axis double TMA"
Author(s): Toshihiro Tsuzuki; Ryuji Suzuki; Hiroki Harakawa; Bungo Ikenoue; James Larkin; Anna Moore; Yoshiyuki Obuchi; Andrew C. Phillips; Sakae Saito; Fumihiro Uraguchi; James Wincentsen; Shelley Wright; Yutaka Hayano
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Paper Abstract

IRIS (InfraRed Imaging Spectrograph) is one of the first-generation instruments for the Thirty Meter Telescope (TMT). IRIS is composed of a combination of near-infrared (0.84-2.4 μm) diffraction limited imager and integral field spectrograph. To achieve near-diffraction limited resolutions in the near-infrared wavelength region, IRIS uses the advanced adaptive optics system NFIRAOS (Narrow Field Infrared Adaptive Optics System) and integrated on-instrument wavefront sensors (OIWFS). However, IRIS itself has challenging specifications. First, the overall system wavefront error should be less than 40 nm in Y, z, J, and H-band and 42 nm in K-band over a 34.0 × 34.0 arcsecond field of view. Second, the throughput of the imager components should be more than 42 percent. To achieve the extremely low wavefront error and high throughput, all reflective design has been newly proposed. We have adopted a new design policy called "Co-Axis double-TMA", which cancels the asymmetric aberrations generated by "collimator/TMA" and "camera/TMA" efficiently. The latest imager design meets all specifications, and, in particular, the wavefront error is less than 17.3 nm and throughput is more than 50.8 percent. However, to meet the specification of wavefront error and throughput as built performance, the IRIS imager requires both mirrors with low surface irregularity after high-reflection coating in cryogenic and high-level Assembly Integration and Verification (AIV). To deal with these technical challenges, we have done the tolerance analysis and found that total pass rate is almost 99 percent in the case of gauss distribution and more than 90 percent in the case of parabolic distribution using four compensators. We also have made an AIV plan and feasibility check of the optical elements. In this paper, we will present the details of this optical system.

Paper Details

Date Published: 4 August 2016
PDF: 18 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 9908AE (4 August 2016); doi: 10.1117/12.2232491
Show Author Affiliations
Toshihiro Tsuzuki, National Astronomical Observatory of Japan (Japan)
Ryuji Suzuki, National Astronomical Observatory of Japan (Japan)
Hiroki Harakawa, National Astronomical Observatory of Japan (Japan)
Bungo Ikenoue, National Astronomical Observatory of Japan (Japan)
James Larkin, Univ. of California, Los Angeles (United States)
Anna Moore, Caltech Optical Observatories (United States)
Yoshiyuki Obuchi, National Astronomical Observatory of Japan (Japan)
Andrew C. Phillips, Univ. of California Observatories (United States)
Sakae Saito, National Astronomical Observatory of Japan (Japan)
Fumihiro Uraguchi, National Astronomical Observatory of Japan (Japan)
James Wincentsen, Caltech Optical Observatories (United States)
Shelley Wright, Univ. of California, San Diego (United States)
Yutaka Hayano, National Astronomical Observatory of Japan (Japan)


Published in SPIE Proceedings Vol. 9908:
Ground-based and Airborne Instrumentation for Astronomy VI
Christopher J. Evans; Luc Simard; Hideki Takami, Editor(s)

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