In late 1995, the National Solar Observatory and the USAF Phillips Lab group at Sac Peak began the co-operative development of an active optics system for the Vacuum Tower Telescope. Although the immediate objective of this project is to provide a system for sensing and correcting the slowly varying aberrations in the optical system of the VTT, the system is also intended to provide a platform for further development of a full atmospheric compensation system for use in solar imaging. A correlating 69-subaperture Shack-Hartmann wavefront sensor, capable of using solar granulation as its target, and a 97-actuator deformable mirror, manufactured by Xinetics, Inc, are the key components of the new system. During March 1997, the control loop was closed for the first time at the VTT. The ability of the active optics system to improve the resolution performance of the VTT using both a small sunspot and granulation as the wavefront sensing target was successfully demonstrated. The illustration shows corrected and uncorrected G-band (430 nm) solar granulation images, obtained under comparable seeing conditions. The principal telescope aberrations in this test were introduced by the uncooled entrance window of the VTT. We believe that the corrected telescope was compensated to better than 1/10 wave by the active optics system during this test.
Thomas Rimmele, Richard Radick (USAF/PL)