5 July 2000 VLTI pupil transfer: variable curvature mirrors: II. Plasticity, hysteresis, and curvature control
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Progress in Active Optics Methods have led to the invention of Variable Curvature Mirrors. VCMs are useful to provide optical path compensations of the imaged field of view. Preliminarily developed for Fourier transform IR spectrometers, they are now used for the coherent beam recombination of the VLT array. With the VLT Interferometer, a highly flexible VCM will be installed at the focal surface of each cat's eye delay lines. The VCM developments led to the design choice of metal substrates in a quenched state which are at least 15 times more flexible--to external loading--than gloss or vitroceram substrates and thus, have provided accurately the large zoom-range from f/(infinity) to f/2.6. Due to the very large zoom range provided by such active mirrors, it has been found necessary to take under consideration the small plastical deformation as well as the small hysterese loop deformation of the metal substrate. With the four VCMs such as now built for the 8 m telescopes, a plastical deformation model and a hysterese loop model have been determined and are presently described. Including these compensations, the VCM optical figures have been improved and the control software now performs a curvature resolution in between 10-3 and 5 10-4.
© (2000) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Gerard R. Lemaitre, Gerard R. Lemaitre, Marc Ferrari, Marc Ferrari, Silvio P. Mazzanti, Silvio P. Mazzanti, Patrick Lanzoni, Patrick Lanzoni, Patrice Joulie, Patrice Joulie, Denis Leduc, Denis Leduc, Myriam Copede, Myriam Copede, "VLTI pupil transfer: variable curvature mirrors: II. Plasticity, hysteresis, and curvature control", Proc. SPIE 4006, Interferometry in Optical Astronomy, (5 July 2000); doi: 10.1117/12.390208; https://doi.org/10.1117/12.390208


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