Design and manufacturing of a multi-zone phase-shifting coronagraph mask for extremely large telescopes

P. Martinez, M. Beaulieu, K. Barjot, O. Guyon, C. Gouvret, A. Marcotto, M. Belhadi, A. Caillat, T. Behaghel, S. Tisserand, V. Sauget, S. Gautier, J. M. Le Duigou, J. M. Knight, K. Dohlen, A. Vigan, L. Abe, O. Preis, A. Spang, J. DejongheM. N'Diaye

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Article numberA126
JournalAstronomy and astrophysics
Volume635
DOIs
StatePublished - Mar 1 2020

Keywords

  • Instrumentation: high angular resolution
  • Techniques: high angular resolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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