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Proceedings Paper

The 2012 status of the MCAO testbed for the GREGOR solar telescope
Author(s): Dirk Schmidt; Thomas Berkefeld; Frank Heidecke
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Paper Abstract

We look back on two years of experience with the laboratory MCAO testbed for the GREGOR solar telescope. GREGOR’s MCAO features four adaptive mirrors, i. e. one tip-tilt mirror, and three DMs to compensate for turbulence around 0 km, 5 km, and 15.5 km above ground. Two different Hartmann-Shack wavefront sensor units are used for wavefront tomography. A sensor with a narrow field of view and smaller subapertures is dedicated to high-order aberrations on the optical axis. This sensor directly follows the pupil plane DM and does not see the high-altitude DMs. The second sensor features larger subapertures and 19 guide regions spread over a wide field of view for off-axis wavefront sensing. We show that high-altitude DMs cause rapidly changing pupil distortions and thus misregistration, which renders the interaction of a pupil-plane DM and a subsequent wavefront sensor non-linear. We rewrote the control software for cleaner and more flexible code, and we switched to modal wavefront reconstruction from direct reconstruction. The original digital interfacing of the DMs high-voltage electronics didn’t prove to be reliable. Thus, we developed a new interface board that is based on CameraLink/ChannelLink technology to transmit the DM commands from the control computer. In this paper we present the innovations and some of the first experimental performance measurements with two DMs. One DM failed before scientific grade data was recorded with three DMs. This DM will be replaced soon. We conclude that GREGOR’s MCAO system is now ready for first on-sky tests at the telescope.

Paper Details

Date Published: 13 September 2012
PDF: 11 pages
Proc. SPIE 8447, Adaptive Optics Systems III, 84473J (13 September 2012); doi: 10.1117/12.926902
Show Author Affiliations
Dirk Schmidt, Kiepenheuer-Institut für Sonnenphysik (Germany)
Thomas Berkefeld, Kiepenheuer-Institut für Sonnenphysik (Germany)
Frank Heidecke, Kiepenheuer-Institut für Sonnenphysik (Germany)


Published in SPIE Proceedings Vol. 8447:
Adaptive Optics Systems III
Brent L. Ellerbroek; Enrico Marchetti; Jean-Pierre Véran, Editor(s)

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