The Gemini MCAO bench: system overview and lab integration

Abstract

We present Canopus, the AO bench for Gemini's Multi Conjugate Adaptive Optics System (GEMS), a unique facility for the Gemini South telescope located at Cerro Pachon in Chile. The MCAO system uses five laser beacons in conjunction with different natural guide stars configurations. A deployable fold mirror located in the telescope Acquisition and Guiding Unit (A&G) sends the telescope beam to the entrance of the bench. The beam is split within Canopus into three main components: two sensing paths and the output corrected science beam. Light from the laser constellation (589nm) is directed to five Shack-Hartman wave front sensors (E2V-39 CCDs read at 800Hz). Visible light from natural guide stars is sent to three independent sensors arrays (SCPM AQ4C Avalanche Photodiodes modules in quad cell arrangement) via optical fibers mounted on independent stages and a slow focus sensor (E2V-57 back-illuminated CCD). The infrared corrected beam exits Canopus and goes to instrumentation for science. The Real Time Controller (RTC) analyses wavefront signals and correct distortions using a fast tip-tilt mirror and three deformable mirrors conjugated at different altitudes. The RTC also adjusts positioning of the laser beacon (Beam Transfer Optics fast steering array), and handles miscellaneous offloads (M1 figure, M2 tip/tilt, LGS zoom and magnification corrections, NGS probes adjustments etc.). Background optimizations run on a separate dedicated server to feed new parameters into the RTC.