MMT adaptive secondary: performance evaluation and field testing G. Brusa a,b A. Riccardi b , P. Salinari b , F. P. Wildi a , M. Lloyd-Hart a , H. M. Martin a , R. Allen a , D. Fisher a , D. L. Miller a , R. Biasi c , D. Gallieni d , F. Zocchi e a Steward Observatory/Univ. of Arizona, 933 Cherry Av., Tucson AZ, 85721, USA b Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, 50125 Firenze, Italy c Microgate S.r.l, Via Valdagno 4, 39100 Bolzano, Italy d ADS International S.r.L., Corso Promessi Sposi 23/d, 22053 Lecco, Italy e Media Lario S.r.l, Localit´ a Pascolo, 23842 Bosisio Parini, Italy ABSTRACT 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 paper ? also presented at this conference. Keywords: adaptive optics, deformable mirrors, adaptive secondary mirrors, electromagnetic actuators, ca- pacitive sensors 1. INTRODUCTION The development of an adaptive secondary as a wavefront corrector was started approximately two years after a seminal paper ? was describing its general structure and a practical implementation. Initially, very simple prototypes were developed to check the soundness of the idea. ? Later a first convex prototype was designed and tested in Arcetri (Italy), ? the promising results obtained prompted the development of an adaptive secondary for the Multiple Mirror Telescope in 1998. Since then much work has been devoted to the realization of a prototype with 36 actuators (P36) ?, ? and to the final unit (MM336) ? that was ready for initial testing in July 2000. Two years later we are now at the final stage of development when a complete characterization is possible and improvements and upgrades are to be determined. This paper reports on last year’s testing activity of the mirror at a specially designed optical test tower ? where the mirror was tested with the rest of the elements that compose the AO system designed for the MMT telescope. ?, ? We will also briefly report on the first attempt Further author information: (Send correspondence to G.B.) G.B.: E-mail: gbrusa@as.arizona.edu, Telephone: ++1 520 626 9529 A.R.: E-mail: riccardi@arcetri.astro.it