Variable curvature mirrors: implementation in the VLTI delay-lines for field compensation

Marc Ferrari; Gerard R. Lemaitre; Silvio P. Mazzanti; Frederic Derie; Alexis Huxley; J. Lemerrer; Patrick Lanzoni; Pascal Dargent; Anders Wallander

doi:10.1117/12.458246

21 February 2003 Variable curvature mirrors: implementation in the VLTI delay-lines for field compensation

Marc Ferrari, Gerard R. Lemaitre, Silvio P. Mazzanti, Frederic Derie, Alexis Huxley, J. Lemerrer, Patrick Lanzoni, Pascal Dargent, Anders Wallander

Author Affiliations +

Proceedings Volume 4838, Interferometry for Optical Astronomy II; (2003) https://doi.org/10.1117/12.458246
Event: Astronomical Telescopes and Instrumentation, 2002, Waikoloa, Hawai'i, United States

Abstract

As the result of an analysis pursued from the very beginning, today the VLT Interferometer is the only interferometer allowing to have a 2 arcsec interferometric field of view (f.o.v) available at the instruments entrance. This accessible interferometric field is the direct result of a careful pupil transfer from the individual telescopes to the central laboratory, unique feature of the VLTI. For this goal it has been necessary to develop a new optical device, the Variable Curvature Mirror (VCM.), using large deformation theory of elasticity, and advanced techniques in optical fabrication. The possibility with the VLTI to use various baselines, from 8 to 200 m with UTs or ATs, leads to severe conditions on the VCM curvature range. A given delay-line, and its associated VCM, should be able to transfer a pupil to the interferometric laboratory from a very far or relatively close position of an ATs. Considering the f.o.v required in the VLTI (2 arcsec), the delay-lines strokes or the OPD to compensate for, and the various locations of the UTs and ATs stations, the curvature of the VCM has to be continuously variable within a range from 84 mm^-1 to 2800 mm^-1. The location of the VCM in the delay-line system, on the piezo-translator used for small OPD compensation, led to minimize its dimensions and to realize a small active mirror with a 16mm diameter. With this small optical aperture, the VCM range of curvature corresponds to a f ratio from f/∞ to f/2.625. The two first VCM complete systems (mirror, mechanics and control command software) have been achieved in 2001/2002 and will be installed in the VLTI delay-lines during fall 2002. Their final performances (optical quality, pupil transfer accuracy, etc.) are reviewed.

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Marc Ferrari, Gerard R. Lemaitre, Silvio P. Mazzanti, Frederic Derie, Alexis Huxley, J. Lemerrer, Patrick Lanzoni, Pascal Dargent, and Anders Wallander "Variable curvature mirrors: implementation in the VLTI delay-lines for field compensation", Proc. SPIE 4838, Interferometry for Optical Astronomy II, (21 February 2003); https://doi.org/10.1117/12.458246

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