MMT adaptive secondary: Performance evaluation and field testing

G. Brusa, A. Riccardi, P. Salinari, F. P. Wildi, M. Lloyd-Hart, H. M. Martin, R. Allen, D. Fisher, D. L. Miller, R. Biasi, D. Gallieni, F. Zocchi

Research output: Contribution to journalConference articlepeer-review

48 Scopus citations


The adaptive secondary for the MMT (called MMT336) is the first mirror of its kind. It was designed to allow the application of wavefront corrections (including tip-tilt) directly at the secondary mirror location. Among the advantages of such a choice for adaptive optics operation are higher throughput, lower emissivity, and simpler optical setup. The mirror also has capabilities that are not found in most correctors including internal position feedback, large stroke (to allow chopping) and provision for absolute position calibration. The 336 actuator adaptive secondary for MMT has been used daily for over one year in our adaptive optics testing facility which has built confidence in the mirror operation and allowed us to interface it to the MMT adaptive optics system. Here we present the most recent data acquired in the lab on the mirror performance. By using interferometer measurements we were able to achieve a residual surface error of approximately 40nm rms. Coupling the mirror with a Shack-Hartmann wavefront sensor we obtained a stable closed loop operation with a -3dB closed loop bandwidth of approximately 30Hz limited by the wavefront sensor frame rate. We also present some preliminary results that show a 5Hz, 90% duty cycle, ±5 arcsec chopping of the mirror. Finally the experience gained and the problems encountered during the first light adaptive optics run at the telescope will be briefly summarized. A more extensive report can be found in another paper1 also presented at this conference.

Original languageEnglish (US)
Pages (from-to)691-702
Number of pages12
JournalProceedings of SPIE - The International Society for Optical Engineering
Issue number2
StatePublished - Dec 1 2002
EventAdaptive Optical System Technologies II - Waikoloa, HI, United States
Duration: Aug 22 2002Aug 26 2002


  • Adaptive optics
  • Adaptive secondary mirrors
  • Capacitive sensors
  • Deformable mirrors
  • Electromagnetic actuators

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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