ELTs have the potential for imaging reflected light from habitable rocky planets around M-stars. To address that exciting science we present the PDR level optical-mechanical design for a high-contrast coronagraphic instrument for the 25.4m Giant Magellan Telescope (GMT) called GMagAO-X. It is a first light extreme adaptive optics (ExAO) coronagraphic instrument which mounts to the sector D folded port of the GMT. To meet the strict ExAO fitting and servo error requirement (<90nm rms WFE), GMagAO-X must have 21,000 actuator DM capable of >2KHz update speeds. To minimize wavefront/segment piston error GMagAO-X has an interferometric beam combiner on a vibration isolated table, as part of this 21,000 actuator “parallel DM”. Segment/petal piston errors are continuously sensed by a novel Holographic Dispersed Fringe Sensor (HDFS). In addition to a coronagraph, it has a post-coronagraphic Lyot Low Order WFS (LLOWFS) to sense non-common path (NCP) errors. The LLOWFS drives a non-common path DM (NCP DM) to correct those NCP errors. GMagAO-X obtains high-contrast science and wavefront sensing in the visible or the NIR. Here we present our successful, externally reviewed (Feb. 2024), PDR optical-mechanical design that satisfies GMagAO-X’s top-level science requirements and is compliant with the GMT instrument requirements/ICDs and only requires COTS parts and readily available 2-5 inch sized optics. We have also prototyped the parallel DM and the HDFS phasing sensor on the HCAT testbed. We show initial phased HCAT testbed results for the parallel DM and initial on-sky phasing results for HDFS.
GMagAO-X is the ExAO coronagraphic instrument for the 25.4m GMT. It is designed for a slot on the folded port of the GMT. To meet the strict ExAO fitting and servo error requirement (<90nm rms WFE), GMagAO-X must have 21,000 actuator DM capable of ≥2KHz correction speeds. To minimize wavefront/segment piston error GMagAO-X has an interferometric beam combiner on a vibration isolated table, as part of this “21,000 actuator parallel DM”. Piston errors
are sensed by a Holographic Dispersed Fringe Sensor (HDFS). In addition to a coronagraph, it has a post-coronagraphic Low Order WFS (LLOWFS) to sense non-common path (NCP) errors. The LLOWFS drives a non-common path DM (NCP DM) to correct those NCP errors. GMagAO-X obtains high-contrast science and wavefront sensing in the visible and/or the NIR. Here we present our successful externally reviewed (Sept. 2021) CoDR optical-mechanical design that satisfies GMagAO-X’s top-level science requirements and is compliant with the GMT instrument requirements and only requires COTS parts.
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