Infrared Optics Design for the Japan National Large Telescope Project

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National Astronomical Observatory of Japan (NAOJ) is constructing an 8m reflector at the summit of Mauna Kea in Hawaii which is known to be most suitable site for infrared observation. Dr. Nariai stayed in Hawaii and collaborated with staff members of University of Hawaii and of Mauna Kea Observatories in evaluating infrared data of existing telescopes and Mauna Kea sky, and in designing optical systems for the Japan National Large Telescope (JNLT).The design work resulted in an F/12.2 and a chopping F/35 IR mirror system, for the latter of which active deformation of the main mirror was introduced in order to secure defraction-limit resolution of direct images in mid-IR (-0."2) using quickly developing 2-D array detectors.A wide-field corrector for IR observation at the primary focus was also designed by adopting new glass material for the first time.In order to minimize the instrumental thermal noise background, various devices were recommended, but some crucial issues, such as depletion of radiation from structures supporting the secondary and the tertiary mirrors, remained to be investigated in follow-on tasks.