23 July 2008 Development of surface metrology for the Giant Magellan Telescope primary mirror
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Abstract
The Giant Magellan Telescope achieves 25 meter aperture and modest length using an f/0.7 primary mirror made from 8.4 meter diameter segments. The systems that will be used for measuring the aspheric optical surfaces of these mirrors are in the final phase of development. This paper discusses the overall metrology plan and shows details for the development of the principal test system - a system that uses mirrors and holograms to provide a null interferometric test of the surface. This system provides a full aperture interferometric measurement of the off-axis segments by compensating the 14.5 mm aspheric departure with a tilted 3.8-m diameter powered mirror, a 77 cm tilted mirror, and a computer generated hologram. The interferometric measurements are corroborated with a scanning slope measurement from a scanning pentaprism system and a direct measurement system based on a laser tracker.
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J. H. Burge, J. H. Burge, W. Davison, W. Davison, H. M. Martin, H. M. Martin, C. Zhao, C. Zhao, } "Development of surface metrology for the Giant Magellan Telescope primary mirror", Proc. SPIE 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 701814 (23 July 2008); doi: 10.1117/12.790082; https://doi.org/10.1117/12.790082
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