Volume 635, March 2020
|Number of page(s)||11|
|Published online||19 March 2020|
Design and manufacturing of a multi-zone phase-shifting coronagraph mask for extremely large telescopes
Université Côte d’Azur, Observatoire de la Côte d’Azur, CNRS, Laboratoire Lagrange, Nice, France
2 Astrobiology Center, National Institutes of Natural Sciences, 2-21-1, Osawa, Mitaka, Tokyo, Japan
3 Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
4 National Astronomical Observatory of Japan, Subaru Telescope, National Institutes of Natural Sciences, Hilo, HI 96720, USA
5 Aix Marseille Univ., CNRS, CNES, LAM, Marseille, France
6 Silios Technologies, Rue Gaston Imbert prolonge, ZI de Peynier-Rousset, 13790 Peynier, France
7 Centre National d’Etudes Spatiales, 18 avenue Edouard Belin, 31401 Toulouse cedex 9, France
8 University of Arizona, Steward Observatory, 933 N. Cherry Ave., Tucson, AZ 85719, USA
Accepted: 30 January 2020
Context. High-contrast imaging of exoplanets around nearby stars with future large-segmented apertures requires starlight suppression systems optimized for complex aperture geometries. Future extremely large telescopes (ELTs) equipped with high-contrast instruments operating as close as possible to the diffraction limit will open a bulk of targets in the habitable zone around M-stars. In this context, the phase-induced amplitude apodization complex mask coronagraph (PIAACMC) is a promising concept for high-efficiency coronagraphic imaging at small angular separations with segmented telescopes.
Aims. The complex focal plane mask of the PIAACMC is a multi-zone, phase-shifting mask comprised of tiled hexagons that vary in depth. The mask requires micro-fabrication techniques because it is generally made of hundreds micron-scale hexagonal zones with depths ranging over a few microns. We aim to demonstrate that the complex focal plane mask of a PIAACMC with a small inner working angle can be designed and manufactured for segmented apertures.
Methods. We report on the numerical design, specifications, manufacturing, and characterization of a PIAACMC complex focal plane mask for the segmented pupil experiment for exoplanet detection facility.
Results. Our PIAACMC design offers an inner working angle of 1.3 λ/D and is optimized for a 30% telescope-central-obscuration ratio including six secondary support structures (ESO/ELT design). The fabricated reflective focal plane mask is made of 499 hexagons, and the characteristic size of the mask features is 25 μm, with depths ranging over ±0.4 μm. The mask sag local deviation is measured to an average error of 3 nm and standard deviation of 6 nm rms. The metrological analysis of the mask using interferential microscopy gives access to an in-depth understanding of the component’s optical quality, including a complete mapping of the zone depth distribution zone-depth distribution. The amplitude of the errors in the fabricated mask are within the wavefront control dynamic range.
Conclusions. We demonstrate the feasibility of fabricating and characterizing high-quality PIAA complex focal plane masks.
Key words: instrumentation: high angular resolution / techniques: high angular resolution
© P. Martinez et al. 2020
Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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