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23 July 2008 Stress polishing of toric mirrors for the VLT-SPHERE common path
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Abstract
The very challenging goal of the Vlt-Sphere instrument, Exoplanet direct detection and characterisation, requires high contrast imaging and extreme adaptive optics.1 In order not to limit the overall imaging performances of the instrument, all the optics in the common path optical train need to be of the better quality over each range of spatial frequencies. Three Toric mirrors are placed in the common path to relay the beam to the deformable mirror and to the instruments. This paper details the Stress polishing principle developed at Laboratoire d'Astrophysique de Marseille (Lam) to get the better optical quality on the toric surfaces, using a spherical polishing with full size tools. The elasticity theory giving the optimisation of the blank geometry to be warped during the stress polishing process is detailed from analytical calculation to finite element analysis. The use of an angular thickness distribution allows us to reach the better optical quality of the deformation by canceling higher order terms. We also present the polishing results for the 366mm diameter Toric Mirror manufacturing.
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Emmanuel Hugot, Marc Ferrari, Kacem El Hadi, Kjetil Dohlen, Pascal Vola, Nicolas Ernst, Gérard R. Lemaitre, and Pierre Montiel "Stress polishing of toric mirrors for the VLT-SPHERE common path", Proc. SPIE 7018, Advanced Optical and Mechanical Technologies in Telescopes and Instrumentation, 701806 (23 July 2008); https://doi.org/10.1117/12.787607
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