Laboratory demonstration of a mid-infrared AGPM vector vortex coronagraph
Abstract
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.
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.Attached Files
Published - aa21126-13.pdf
Submitted - 1304.1180v1.pdf
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Additional details
- Eprint ID
- 57712
- Resolver ID
- CaltechAUTHORS:20150520-123604518
- Fonds de la Recherche Scientifique (FNRS)
- Fonds de solidarité ULg
- Swedish Diamond Centre
- Uppsala University
- Communauté française de Belgique – Actions de recherche concertées – Académie universitaire Wallonie-Europe
- Created
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2015-05-20Created from EPrint's datestamp field
- Updated
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2021-11-10Created from EPrint's last_modified field