Laser-based adaptive optics system for the 6.5 m MMT

The Multiple Mirror Telescope (MMT) will be converted to a single-mirror telescope in early 1998. Adaptive optics using a sodium laser guide star will be an integral part of the new telescope with adaptive correction made at the secondary mirror. The MMT AO system is under development, and will be completed for sky tests soon after telescope first light. In this paper, we give an overview of the system and present the status of major components. We also show results of adaptive correction with a sodium beacon laser using a prototype AO system. The 6.5 m system is based on a 300actuator adaptive secondary mirror; a 60 actuator, 53 cm prototype is currently undergoing tests. The use of a low-noise CCD for wavefront sensing, and an infrared quad cell for global image motion sensing will be reviewed. Two lasers will be available for use at the telescope. One is a 4 W CW dye laser, currently used by our group. The second laser, being built by Lite Cycles, will be a 10 W diode-pumped mode-locked YAG, with Raman shifting by calcium tungstate. The expected performance of the AO system will be reviewed.