The Gemini MCAO bench: system overview and lab integration
2008
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.
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