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Proceedings Paper

Testing of the Gemini secondary mirrors
Author(s): Wolfgang Otto
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Paper Abstract

The first 1-m secondary mirror for the Gemini 8-m telescopes project was delivered by Zeiss in 1998, and 2nd mirror will be delivered in the summer of 1999. For first use during commissioning we produced an extreme lightweight Zerodur solution prefabricated at Schott. To reach the 85 percent weight reduction a novel etching technique was used. INterferometric testing was done performing full aperture measurements using a concave matrix. In progress with the fabrication process of the matrix we applied 3D-mechanical measurements, IR-interferometry, and VIS-interferometry using null lenses to reach the final intrinsic quality of 6 nm rms. For interferometric testing of the secondaries phase shifting interferometry with a tunable laser diode was applied. The optical test results of the secondaries show, that the mirrors are well within specification. The finally achieved intrinsic surface quality is 17 nm rms for Unit 1 and 13 nm rms for Unit 2, dominated by cutting effects which were introduced by removing the oversize at the inner and outer edge of the mirror after the final polishing step.

Paper Details

Date Published: 6 September 1999
PDF: 5 pages
Proc. SPIE 3739, Optical Fabrication and Testing, (6 September 1999); doi: 10.1117/12.360160
Show Author Affiliations
Wolfgang Otto, Carl Zeiss (Germany)

Published in SPIE Proceedings Vol. 3739:
Optical Fabrication and Testing
Roland Geyl; Jonathan Maxwell, Editor(s)

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