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Phase-induced amplitude apodization complex-mask coronagraphy for the Magellan extreme adaptive optics instrument and the giant Magellan telescope: design and fabrication (Conference Presentation)
Author(s): Justin Knight; Olivier Guyon; Jared Males
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Paper Abstract

Phase-Induced Amplitude Apodization Complex-Mask Coronagraph (PIAACMC) designs provide the high-contrast required to directly image exoplanets over a region of interest at a small inner-working angle (IWA) while preserving planet throughput. A PIAACMC consists of a set of optics designed to work in relayed pupil and image planes, with several components which are challenging to fabricate. The optical design for PIAACMC is a two-stage set of aspheric optics responsible for lossless apodization by beam profile re-shaping, followed by a multi-zone focal plane mask (FPM) which alters the phase and amplitude of the incident light field across each zone using optical path length delays. Each zone corresponds to an optical path difference such that their combined effect in the science plane produces a broadband null - up to 20% in recent designs. A Lyot stop follows to further filter the diffracted starlight, or use it in a feedback loop for minimizing low-order aberrations such as wavefront tip and tilt. Finally, a set of inverse-PIAA optics may be implemented to restore the original beam profile to image the science plane unaffected by the distortions induced by the PIAA optics. The aspheric profiles of the PIAA and inverse-PIAA optics are reduced by the introduction of the multi-zone complex FPM; all of these are custom optics which require care to fabricate to within a few percent of their ideal design surface profiles. However, the cost of fabrication and implementation can be well worth the effort because in addition to small IWA performance, PIAACMC designs are robust against the increasingly complicated telescope pupil architectures being developed for future generation telescopes. PIAACMC has been successfully fabricated for and installed at the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument at the Subaru telescope, and, among other places, is being developed for segmented telescope architectures at the NASA Ames Coronagraph Experiment (ACE) testbed. We are now developing a design for MagAO-X, a 2000 actuator ExAO system on a 6.5 m telescope aperture at the Las Campanas Observatory in Chile; MagAO-X will deliver Strehl ratios above 70% with high-resolutions ranging between 14 and 30 mas. Similarly, the system contrast requirements are at least 10-4 between ~1 and 10 λ/D. MagAO-X, as well as the future generation Giant Magellan Telescope (GMT) offer opportunities to field-test design changes, and demonstrate the robustness of PIAACMC to telescope pupils with complicated architectures including segments, spiders, and secondary obscurations. We present designs for MagAO-X and GMT, discussing improvements in their design toward producing easily manufactureable components. Moreover for MagAO-X, we present the current state of fabrication for the PIAACMC with predictive models of performance from surface profile measurements of the custom optics.

Paper Details

Date Published: 10 July 2018
Proc. SPIE 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III, 107062Q (10 July 2018); doi: 10.1117/12.2313693
Show Author Affiliations
Justin Knight, The Univ. of Arizona (United States)
Olivier Guyon, The Univ. of Arizona (United States)
Jared Males, The Univ. of Arizona (United States)

Published in SPIE Proceedings Vol. 10706:
Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III
Ramón Navarro; Roland Geyl, Editor(s)

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