Astronomy; Diamond microfabrication; Exoplanets; Infrared optics; Optical gratings; Reactive ion etching; Direct observations; Extremely Large Telescopes; Micro-fabrication; Phase masks; Reactive-ion etching
Abstract :
[en] Direct observation of exoplanets and proto-planetary disks with the METIS instrument at the Extremely Large Telescope will provide new insights into the processes of planet formation and exoplanet atmospheres. This will be possible thanks to a powerful vector vortex coronagraph that can suppress the starlight to reveal faint signals around it. Here we present the process of making the phase masks at the heart of the coronagraph. These annular groove phase masks consist of deep sub-wavelength gratings in diamond that are etched using inductively coupled oxygen plasma with a strong bias. The METIS instrument requires a wider bandwidth than such components have previously been demonstrated for, leading to a grating design with higher aspect ratio and more vertical walls. To achieve this, the etch mask used for diamond etching was changed from aluminium to silicon and the plasma power was increased. We also improved on our method for reducing the grating depth of finished components to fine-tune them. Together with improved optical testing, this allowed us to produce the best vortex phase masks so far demonstrated for the astronomical N-band.
Research Center/Unit :
STAR - Space sciences, Technologies and Astrophysics Research - ULiège
Disciplines :
Materials science & engineering
Author, co-author :
Forsberg, Pontus; Department of Materials Science and Engineering, Uppsala University, Sweden
Karvinen, Petri; Center for Photonics Sciences, University of Eastern Finland, Finland
Ronayette, Samuel; Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Gif-sur-Yvette, France
Kuittinen, Markku; Center for Photonics Sciences, University of Eastern Finland, Finland
Absil, Olivier ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO)
König, Lorenzo; STAR Institute, University of Liège, Belgium
Delacroix, Christian ; Université de Liège - ULiège > Département d'astrophysique, géophysique et océanographie (AGO) > Planetary & Stellar systems Imaging Laboratory
Orban De Xivry, Gilles ; Université de Liège - ULiège > Unités de recherche interfacultaires > Space sciences, Technologies and Astrophysics Research (STAR)
Barrière, Jean-Christophe; Université Paris-Saclay, CEA, DRF/IRFU/DIS, Gif-sur-Yvette, France
Pantin, Eric; Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, Gif-sur-Yvette, France
Karlsson, Mikael; Department of Materials Science and Engineering, Uppsala University, Sweden
Language :
English
Title :
Making the diamond vortex phase masks for the METIS instrument
The authors gratefully acknowledge funding from the Research Council of Finland Flagship Programme, Photonics Research and Innovation (PREIN), decision number 346518 and the Swedish-French Foundation. This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No 819155), and the European Southern Observatory.
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