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Research Paper

Journal of the Optical Society of Korea 2009; 13(2): 178-183

Published online June 25, 2009 https://doi.org/10.3807/JOSK.2009.13.2.178

Copyright © Optical Society of Korea.

Accuracy Assessment for Measuring Surface Figures of Large Aspheric Mirrors

Young-Soo Kim1, Ki-Beom Ahn1, Kwi-Jong Park1, Il-Kweon Moon2, and Ho-Soon Yang2

1Korea Astronomy & Space Science Institute; 2Korea Research Institute of Standards and Science

Received: May 19, 2009; Revised: June 17, 2009; Accepted: June 18, 2009

At the time that the Keck-I 10m telescope was constructed in 1993, the era of Very Large Telescopes (VLTs) was opened. Now thirteen VLTs are in operation, and the largest of the monolithic mirrors is 8.4 m in diameter. Such monolithic mirrors are mostly aspheric and require high accuracies on the surface figures, reaching up to the diffraction limit. At present, next generation telescopes, Giant telescopes, are being developed. One is the GMT (Giant Magellan Telescope) whose size is 25.4 m in diameter. The primary mirror consists of seven segments figuring elliptical shapes on the surface. The surrounding six segments are off-axis and the edges are steep, as the fast focal ratio is adopted. It means that testing of the mirrors is a challenging task. In this paper, testing methods for the GMT primary mirror are reviewed, and accuracy of measuring devices is assessed. Results and discussions follow.

Keywords: Telescope, Mirror, Surface, Accuracy, Aspheric,

OCIS codes: 110.6770; 120.3180; 120.3940; 220.4840

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