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MACAO-VLTI piston issue: achieving the interferometry requirements
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Paper Abstract

MACAO-VLTI is a set of four adaptive optics systems dedicated to interferometry with the ESO 8 meter telescopes in Paranal, Chile. One of the most important requirements for the MACAO-VLTI is to keep the piston variations of the bimorph deformable mirror below 25 nm RMS in a time window of 48 msec. For this purpose, a piston removal algorithm has been developed, that uses a pre-calibrated set of voltages to compensate the natural piston of each influence function. This pre-calibration constitutes a critical laboratory measurement of the influence functions. Using Hadamard matrices, a (64 x 64) Shack-Hartman sensor and a capacitive sensor located at the center of the mirror (back-side), an accuracy better than 1% has been reached to characterize them. Various configurations were investigated to minimize the dynamical residual piston: the control matrix, the loop speed and the loop gain. Particular attention was paid to the influence functions non-linearities. An original indirect method was developed to measure the residual piston in real-time. We present here the methods and results obtained so far.

Paper Details

Date Published: 25 October 2004
PDF: 12 pages
Proc. SPIE 5490, Advancements in Adaptive Optics, (25 October 2004); doi: 10.1117/12.551854
Show Author Affiliations
Liviu Ivanescu, European Southern Observatory (Germany)
Robin Arsenault, European Southern Observatory (Germany)
Enrico Fedrigo, European Southern Observatory (Germany)
Markus E. Kasper, European Southern Observatory (Germany)
Sylvain Oberti, European Southern Observatory (Germany)
Jerome Paufique, European Southern Observatory (Germany)
Stefan Stroebele, European Southern Observatory (Germany)

Published in SPIE Proceedings Vol. 5490:
Advancements in Adaptive Optics
Domenico Bonaccini Calia; Brent L. Ellerbroek; Roberto Ragazzoni, Editor(s)

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