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Laboratory demonstration of a mid-infrared AGPM vector vortex coronagraph

Delacroix, C. and Absil, O. and Forsberg, P. and Mawet, D. and Christiaens, V. and Karlsson, M. and Boccaletti, A. and Baudoz, P. and Kuittinen, M. and Vartiainen, I. and Surdej, J. and Habraken, S. (2013) Laboratory demonstration of a mid-infrared AGPM vector vortex coronagraph. Astronomy and Astrophysics, 553 . Art. No. UNSP A98. ISSN 0004-6361. doi:10.1051/0004-6361/201321126.

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Context. Coronagraphy is a powerful technique to achieve high contrast imaging, hence to image faint companions around bright targets. Various concepts have been used in the visible and near-infrared regimes, while coronagraphic applications in the mid-infrared nowadays remain largely unexplored. Vector vortex phase masks based on concentric subwavelength gratings show great promise for such applications. Aims. We aim at producing and validating the first high-performance broadband focal plane phase mask coronagraphs for applications in the mid-infrared regime, and in particular the L band with a fractional bandwidth of ~16% (3.5–4.1 μm). Methods. Based on rigorous coupled wave analysis, we designed an annular groove phase mask (AGPM) producing a vortex effect in the L band, and etched it onto a series of diamond substrates. The grating parameters were measured by means of scanning electron microscopy. The resulting components were then tested on a mid-infrared coronagraphic test bench. Results. A broadband raw null depth of 2 × 10^(-3) was obtained for our best L-band AGPM after only a few iterations between design and manufacturing. This corresponds to a raw contrast of about 6 × 10^(-5) (10.5 mag) at 2λ/D. This result is fully in line with our projections based on rigorous coupled wave analysis modelling, using the measured grating parameters. The sensitivity to tilt and focus has also been evaluated. Conclusions. After years of technological developments, mid-infrared vector vortex coronagraphs have finally become a reality and live up to our expectations. Based on their measured performance, our L-band AGPMs are now ready to open a new parameter space in exoplanet imaging at major ground-based observatories.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Absil, O.0000-0002-4006-6237
Mawet, D.0000-0002-8895-4735
Christiaens, V.0000-0002-0101-8814
Karlsson, M.0000-0002-2011-0851
Boccaletti, A.0000-0001-9353-2724
Surdej, J.0000-0002-7005-1976
Additional Information:© 2013 ESO. Received 18 January 2013; Accepted 29 March 2013. The first author is grateful to the financial support of the Belgian Fonds de la Recherche Scientifique (FRIA) and Fonds de solidarité ULg. S.H. and J.S. acknowledge support from the Belgian FRS-FNRS FRFC.We also gratefully acknowledge financial support from the Swedish Diamond Centre (financed by Uppsala University), and the Communauté française de Belgique – Actions de recherche concertées – Académie universitaire Wallonie-Europe.
Funding AgencyGrant Number
Fonds de la Recherche Scientifique (FNRS)UNSPECIFIED
Fonds de solidarité ULgUNSPECIFIED
Swedish Diamond CentreUNSPECIFIED
Uppsala UniversityUNSPECIFIED
Communauté française de Belgique – Actions de recherche concertées – Académie universitaire Wallonie-EuropeUNSPECIFIED
Subject Keywords:instrumentation: high angular resolution; planetary systems; planets and satellites: detection
Record Number:CaltechAUTHORS:20150520-123604518
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Official Citation:Delacroix, C., Absil, O., Forsberg, P., Mawet, D., Christiaens, V., Karlsson, M., . . . Habraken, S. (2013). Laboratory demonstration of a mid-infrared AGPM vector vortex coronagraph. A&A, 553, A98.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:57712
Deposited On:20 May 2015 21:18
Last Modified:10 Nov 2021 21:54

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