Active compensation of flexure on the High-Resolution Optical Spectrograph for Gemini

Paolo D'Arrigo; Francisco Diego; David D. Walker

doi:10.1117/12.269021

21 March 1997 Active compensation of flexure on the High-Resolution Optical Spectrograph for Gemini

Paolo D'Arrigo, Francisco Diego, David D. Walker

Proceedings Volume 2871, Optical Telescopes of Today and Tomorrow; (1997) https://doi.org/10.1117/12.269021
Event: Optical Telescopes of Today and Tomorrow, 1996, Landskrona/Hven, Sweden

Abstract

Gravity-induced flexure has been a long-standing challenge in Cassegrain spectrographs at 4-meter class telescopes; it is the more so at the scale of 8-meter telescopes. This is of particular concern for the Gemini high resolution optical spectrograph, which will be Cassegrain-mounted for its routine mode of operation. In this paper we address the general flexure problem, and how to solve it with the use of active optics. We also present the results of an experimental active flexure compensation system for the ISIS (intermediate- dispersion spectroscopic and imaging system) spectrograph on the 4.2 m William Herschel Telescope (WHT). This instrument, called ISAAC (ISIS spectrograph automatic active collimator), is based on the concept of active correction, where spectrum drifts, due to the spectrograph flexing under the effect of gravity, are compensated by the movement of an active optical element (in this case a fine steering tip-tilt collimator mirror). The experiment showed that active compensation can reduce flexure down to less than 3 micrometer over four hours of telescope motions, dramatically improving the spectrograph performance. The results of the experiment are used to discuss a flexure compensation system for the high resolution optical spectrograph (HROS) for the 8 m Gemini telescope.

Citation Download Citation

Paolo D'Arrigo, Francisco Diego, and David D. Walker "Active compensation of flexure on the High-Resolution Optical Spectrograph for Gemini", Proc. SPIE 2871, Optical Telescopes of Today and Tomorrow, (21 March 1997); https://doi.org/10.1117/12.269021

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