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Proceedings Paper

APE: a breadboard to evaluate new phasing technologies for a future European Giant Optical Telescope
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Paper Abstract

The point spread function of a segmented aperture is seriously affected by the misalignment of the segments. Stringent requirements apply to position sensors and their calibration. The Active Phasing Experiment (APE) will be a technical instrument aimed at testing possible phasing techniques for a European Giant Optical Telescope (EGOT) in a representative environment. It will also integrate simultaneous control of segmented and monolithic, active surfaces. A mirror composed of 61 hexagonal segments is conjugated to the primary mirror of the VLT. Each segment can be moved in piston, tip and tilt and can be controlled in open or closed loop. Three new types of Phasing Wave Front Sensors dedicated to the measurement of segmentation errors will be tested, evaluated and compared: a modified Mach-Zehnder sensor developed by the LAM and ESO, a Pyramid Sensor developed by Arcetri, and a Curvature Sensor developed by IAC. A reference metrology developed by FOGALE will be added to measure directly the deformation of the segmented mirror and check the efficiency of the tested wavefront sensors. This metrology will be based on a synthetic wavelength instantaneous phase stepping method. This experiment will first run in the laboratory with point-like polychromatic sources and a turbulence generator. In a second step, it will be mounted at a Nasmyth focus of a VLT unit telescope. These activities are included in a proposal to the European Commission for funding within Framework Program 6.

Paper Details

Date Published: 28 September 2004
PDF: 8 pages
Proc. SPIE 5489, Ground-based Telescopes, (28 September 2004); doi: 10.1117/12.553236
Show Author Affiliations
Frederic Y. J. Gonte, European Southern Observatory (Germany)
Natalia Yaitskova, European Southern Observatory (Germany)
Philippe Dierickx, European Southern Observatory (Germany)
Robert Karban, European Southern Observatory (Germany)
Alain Courteville, Fogale Nanotech (France)
Achim Schumacher, Instituto de Astrofisica de Canarias (Spain)
Nicholas Devaney, Instituto de Astrofisica de Canarias (Spain)
Simone Esposito, INAF, Osservatorio Astrofisico di Arcetri (Italy)
Kjetil Dohlen, Lab. d'Astrophysique de Marseille (France)
Marc Ferrari, Lab. d'Astrophysique de Marseille (France)
Luzma Montoya, Lab. d'Astrophysique de Marseille (France)

Published in SPIE Proceedings Vol. 5489:
Ground-based Telescopes
Jacobus M. Oschmann Jr., Editor(s)

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