Wide-Field Image Compensation with Multiple Laser Guide Stars

We report closed-loop results obtained from the first adaptive optics system to deploy multiple laser guide beacons. The system is mounted on the 6.5 m MMT telescope in Arizona, and is designed to explore advanced altitudeconjugated techniques for wide-field image compensation. Five beacons are made by Rayleigh scattering of laser beams at 532 nm integrated over a range from 20 to 29 km by dynamic refocus of the telescope optics. The return light is analyzed by a unique Shack-Hartmann sensor that places all five beacons on a single detector, with electronic shuttering to implement the beacon range gate. Wavefront correction is applied with the telescope's unique deformable secondary mirror. The system has now begun operations as a tool for astronomical science, in a mode in which the boundary-layer turbulence, close to the telescope, is compensated. Image quality of 0.2-0.3 arc sec is routinely delivered in the near infrared bands from 1.2–2.5 μm over a field of view of 2 arc min. Although it does not reach the diffraction limit, this represents a 3 to 4-fold improvement in resolution over the natural seeing, and a field of view an order of magnitude larger than conventional adaptive optics systems deliver. We present performance metrics including images of the core of the globular cluster M3 where correction is almost uniform across the full field. We describe plans underway to develop the technology further on the twin 8.4 m Large Binocular Telescope and the future 25 m Giant Magellan Telescope.