Interferometric testing of the VLT tertiary mirrors

Stefan Schulte; Bernd Doerband; Frank Schillke; Wolfgang Wiedmann; Alain Michel

doi:10.1117/12.357772

17 August 1999 Interferometric testing of the VLT tertiary mirrors

Stefan Schulte, Bernd Doerband, Frank Schillke, Wolfgang Wiedmann, Alain Michel

Proceedings Volume 3745, Interferometry '99: Applications; (1999) https://doi.org/10.1117/12.357772
Event: International Conference on Optical Metrology, 1999, Pultusk Castle, Poland

Abstract

The tertiary mirrors of the Very Large Telescope, one of the most powerful astronomical telescope systems, were manufactured and tested at Carl Zeiss. These components are lightweight elliptical plane mirrors with diameters of 1250 mm and 880 mm for the long and short axis, respectively. A particular challenge of this project was the outer rim specification of 200 nm peak-to-valley mirror surface deviation. This value had to be obtained under all operational load cases differing in the influence of gravity on the lightweight structure of the mirror. The mirror had to be tested on its support cell. For the absolute calibration of the large plane mirror surface a Ritchey- Common test was performed at two different angular positions. The test setup was adapted as close as possible to the operational position of the mirror in the telescope. A special algorithm for the calculation of the surface figure error from the wavefront data sets was developed. The results and special challenges of the absolute calibration procedure of the mirror surface will be presented and discussed.

Citation Download Citation

Stefan Schulte, Bernd Doerband, Frank Schillke, Wolfgang Wiedmann, and Alain Michel "Interferometric testing of the VLT tertiary mirrors", Proc. SPIE 3745, Interferometry '99: Applications, (17 August 1999); https://doi.org/10.1117/12.357772

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