Measurements of Tilt and Focus for Sodium Beacon Adaptive Optics on the Starfire 3.5 Meter Telescope

Abstract : Telescopes with adaptive optics systems can measure high-order aberrations using an artificial laser beacon without the need for a relatively bright object near the object being imaged. Unfortunately, tilt and focus measurements are difficult to obtain from a laser beacon. One solution is to use light from the object being imaged to measure tilt and focus. We characterize the performance of a Shack-Hartmann wavefront sensor with 2x2 sub-apertures for measuring tilt and focus. Specifically, we implemented this scheme for the sodium beacon adaptive optics upgrade to the Starfire Optical Range (SOR) 3.5 meter telescope. We use a wave-optics simulation to predict the performance of the tilt and focus sensor in the SOR sodium beacon system, and compare the results to laboratory measurements.