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A Mach-Zehnder interferometer based on orbital angular momentum for improved vortex coronagraph efficiency
Univ Liege, Dept Astrophys Geophys & Oceanog, B-4000 Liege, Belgium..
Ctr Rech Lyon CRAL, High Angular Resolut & Stellar Surroundings Astro, F-69561 St Genis Laval, France..
Univ Liege, Dept Astrophys Geophys & Oceanog, B-4000 Liege, Belgium..
CALTECH, Dept Astron, Pasadena, CA 91125 USA..
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2015 (English)In: Techniques And Instrumentation For Detection Of Exoplanets Vii, 2015, 96051JConference paper (Refereed)Text
Abstract [en]

The Annular Groove Phase Mask (AGPM) is a vectorial vortex phase mask. it act, as a half-wave plate with a radial fast axis orientation operating in the mid infrared domain. When placed at the the focus of a telescope element provides a continuous helical phase ramp for an on axis sources, which creates the orbital angular momentum. Thanks to that phase, the intensity of the central source is canceled by a down-stream pupil stop, while the off axis sources are not affected. However due to experimental conditions the nulling is hardly perfect. To improve the null, a Mach-Zehnder interferometer containing Dove prisms differently oriented can be proposed to sort out light based on its orbital angular momentum (OAM). Thanks to the differential rotation of the beam, a 7 phase shift is achieved for the on axis light affected by a non zero OAM Therefore the contrast between the star and its faint companion is enhanced. Nevertheless, due the Dove prisms birefringence, the performance of the interferometer is relatively poor. To solve this problem, we propose to add a birefringent wave-plate in each arm to compensate this birefringence. In this paper, we will develop the mathematical model of the wave front using the Jones formalism. The performance of the interferometer is at first computed for the simple version without the birefringent plate. Then the effect of the birefringent plate is be mathematically described and the performance is re-computed.

Place, publisher, year, edition, pages
2015. 96051J
, Proceedings of SPIE, ISSN 0277-786X ; 9605
Keyword [en]
Orbital angular momentum, Coronagraphy, Interferometry, Birefringence, Polarization
National Category
Accelerator Physics and Instrumentation Astronomy, Astrophysics and Cosmology Engineering and Technology
URN: urn:nbn:se:uu:diva-276966DOI: 10.1117/12.2189329ISI: 000365982800044ISBN: 978-1-62841-771-5OAI: oai:DiVA.org:uu-276966DiVA: diva2:904410
Conference on Techniques and Instrumentation for Detection of Exoplanets VII, AUG 10-13, 2015, San Diego, CA
Available from: 2016-02-18 Created: 2016-02-16 Last updated: 2016-02-25Bibliographically approved

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