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Proceedings Paper

The Infrared Imaging Spectrograph (IRIS) for TMT: multi-tiered wavefront measurements and novel mechanical design
Author(s): Jennifer Dunn; David Andersen; Edward Chapin; Vlad Reshetov; Ramunas Wierzbicki; Glen Herriot; Dean Chalmer; Victor Isbrucker; James E. Larkin; Anna M. Moore; Ryuji Suzuki
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Paper Abstract

The InfraRed Imaging Spectrograph (IRIS) will be the first light adaptive optics instrument on the Thirty Meter Telescope (TMT). IRIS is being built by a collaboration between Caltech, the University of California, NAOJ and NRC Herzberg. In this paper we present novel aspects of the Support Structure, Rotator and On-Instrument Wavefront Sensor systems being developed at NRC Herzberg. IRIS is suspended from the bottom port of the Narrow Field Infrared Adaptive Optics System (NFIRAOS), and provides its own image de-rotation to compensate for sidereal rotation of the focal plane. This arrangement is a challenge because NFIRAOS is designed to host two other science instruments, which imposes strict mass requirements on IRIS. As the mechanical design of all elements has progressed, we have been tasked with keeping the instrument mass under seven tonnes. This requirement has resulted in a mass reduction of 30 percent for the support structure and rotator compared to the most recent IRIS designs. To accomplish this goal, while still being able to withstand earthquakes, we developed a new design with composite materials. As IRIS is a client instrument of NFIRAOS, it benefits from NFIRAOS’s superior AO correction. IRIS plays an important role in providing this correction by sensing low-order aberrations with three On-Instrument Wavefront Sensors (OIWFS). The OIWFS consists of three independently positioned natural guide star wavefront sensor probe arms that patrol a 2-arcminute field of view. We expect tip-tilt measurements from faint stars within the IRIS imager focal plane will further stabilize the delivered image quality. We describe how the use of On-Detector Guide Windows (ODGWs) in the IRIS imaging detector can be incorporated into the AO correction. In this paper, we present our strategies for acquiring and tracking sources with this complex AO system, and for mitigating and measuring the various potential sources of image blur and misalignment due to properties of the mechanical structure and interfaces.

Paper Details

Date Published: 9 August 2016
PDF: 11 pages
Proc. SPIE 9908, Ground-based and Airborne Instrumentation for Astronomy VI, 9908A9 (9 August 2016); doi: 10.1117/12.2234030
Show Author Affiliations
Jennifer Dunn, NRC - Herzberg Astronomy & Astrophysics (Canada)
David Andersen, NRC - Herzberg Astronomy & Astrophysics (Canada)
Edward Chapin, NRC - Herzberg Astronomy & Astrophysics (Canada)
Vlad Reshetov, NRC - Herzberg Astronomy & Astrophysics (Canada)
Ramunas Wierzbicki, NRC - Herzberg Astronomy & Astrophysics (Canada)
Glen Herriot, NRC - Herzberg Astronomy & Astrophysics (Canada)
Dean Chalmer, NRC - Herzberg Astronomy & Astrophysics (Canada)
Victor Isbrucker, Isbrucker Consulting Inc. (Canada)
James E. Larkin, Univ. of California, Los Angeles (United States)
Anna M. Moore, Caltech Optical Observatories (United States)
Ryuji Suzuki, 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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