Michael Lloyd-Hart (University of Arizona), Christoph Baranec (University of Arizona), N. Mark Milton (University of Arizona), Thomas Stalcup (University of Arizona)
Keywords: Adaptive Optics
Abstract:
Key advances in adaptive optics (AO) for both astronomical and military applications will be enabled through the deployment of multiple laser guide stars on a single large-aperture telescope. Wider compensated fields of view than are now seen with conventional AO systems, even those equipped with single laser beacons, will be achieved with less field dependence of the delivered point-spread function. Correction to the diffraction limit over 2 arcminute fields with multi-conjugate AO and partial correction over 10 arcminutes with ground-layer AO are anticipated. In this paper, we will describe the first closed-loop results from an adaptive optics system deploying multiple laser guide stars, anticipated from a telescope run in early July 2007. The system operates on the 6.5 m MMT in Arizona. Five beacons are made by Rayleigh scattering of laser beams at 532 nm integrated over a range from 20 to 30 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. The wavefront sensor divides the 6.5 m telescope pupil into 60 subapertures, with correction possible up to 54 modes using the telescope’s unique deformable secondary mirror. Image compensation at wavelengths of 1.5 microns and longer is anticipated from analysis of previously recorded open-loop data. Global image motion, not sensed by the lasers, is measured from a natural star imaged onto a photon-counting CCD camera. In tests of the real-time tilt loop conducted in April 2007, the limiting magnitude of the system was found to be V=17 for full correction, with some correction remaining down to V=19.
Date of Conference: September 12-15, 2007
Track: Adaptive Optics