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Proceedings Article

Adaptive secondary mirrors for the Large Binocular Telescope

[+] Author Affiliations
Armando Riccardi, Piero Salinari

Osservatorio Astrofisico di Arcetri (Italy)

Guido Brusa

Osservatorio Astrofisico di Arcetri and Ctr. for Astronomical Adaptive Optics/Univ. of Arizona (USA)

Daniele Gallieni

ADS International S.r.l. (Italy)

Roberto Biasi, Mario Andrighettoni

Microgate S.r.l. (Italy)

Hubert M. Martin

Ctr. for Astronomical Adaptive Optics/Univ. of Arizona (USA)

Proc. SPIE 4839, Adaptive Optical System Technologies II, 721 (February 1, 2003); doi:10.1117/12.458961
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From Conference Volume 4839

  • Adaptive Optical System Technologies II
  • Peter L. Wizinowich; Domenico Bonaccini
  • Waikoloa, Hawai'i, United States | August 22, 2002

abstract

The two adaptive secondary (AS) mirrors for LBT (LBT672) represent the new generation of the AS technology. Their design is based on the experience earned during the extensive tests of the previous generation unit (the MMT AS mirror). Both the mechanics and the electronics have been revised, improving the stability, reliability, maintenance and computational power of the system. The deformable mirror of each unit consists of a 1.6mm-thick Zerodur shell having a diameter of 911mm. The front surface is concave to match the Gregorian design of the telescope. Its figure is controlled by 672 electro-magnetic force actuators that are supported and cooled by an aluminum plate. The actuator forces are controlled using a combination of feed-forward and de-centralized closed loop compensation, thanks to the feedback signals from the 672 co-located capacitive position sensors. The surface reference for the capacitive sensors is a 50mm-thick Zerodur shell faced to the back surface of the thin mirror and rigidly connected to the support plate of the actuators. Digital real-time control and unit monitoring is obtained using new custom-made on-board electronics based on new generation 32bit floating-point DSPs. The total computational power (121 Gflop/s) of the LBT672 units allows using the control electronics as wave-front computer without any reduction of the actuator control capability. We report the details of the new features introduced in the LBT672 design and the preliminary laboratory results obtained on a prototype used to test them. Finally the facility in Arcetri to test the final LBT672 units is presented.

© (2003) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
Citation

Armando Riccardi ; Guido Brusa ; Piero Salinari ; Daniele Gallieni ; Roberto Biasi, et al.
"Adaptive secondary mirrors for the Large Binocular Telescope", Proc. SPIE 4839, Adaptive Optical System Technologies II, 721 (February 1, 2003); doi:10.1117/12.458961; http://dx.doi.org/10.1117/12.458961


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