Design and performance of the tip-tilt subsystem for the Keck II telescope adaptive optics system

摘要

Abstract: A tip-tilt control system has been built as part of the adaptive optics system for the Keck II telescope on Mauna Kea in Hawaii. This system is used to correct for wavefront tip-tilt when the adaptive optics system is in the laser guide star mode, and it uses a natural star as the reference. The system consists of a tip-tilt sensor, fast steering mirror, and digital controller. The tip-tilt sensor is based on a quadrant lens assembly with fiber-optics coupling to four photon counting silicon avalanche photodiodes. The fast steering mirror mount has three PZT actuators with position sensor, and an 8 inch Silicon Carbide lightweight mirror. The controller accommodates a range of integration times, and includes automatic light level control, and an adaptive control algorithm which optimizes control performance with changing tilt star image sizes. The design and performance characteristics of a tip- tilt control system for the Keck II telescope are presented. !4