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Development of a subwavelength grating vortex coronagraph of topological charge 4 (SGVC4)
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2014 (English)In: GROUND-BASED AND AIRBORNE INSTRUMENTATION FOR ASTRONOMY V, 2014, Vol. 9147, 91478YConference paper (Refereed)
Abstract [en]

One possible solution to achieve high contrast direct imaging at a small inner working angle (IWA) is to use a vector vortex coronagraph (VVC), which provides a continuous helical phase ramp in the focal plane of the telescope with a phase singularity in its center. Such an optical vortex is characterized by its topological charge, i.e., the number of times the phase accumulates 2 pi radians along a closed path surrounding the singularity. Over the past few years, we have been developing a charge-2 VVC induced by rotationally symmetric subwavelength gratings (SGVC2), also known as the Annular Groove Phase Mask (AGPM). Since 2013, several SGVC2s (or AGPMs) were manufactured using synthetic diamond substrate, then validated on dedicated optical benches, and installed on 10-m class telescopes. Increasing the topological charge seems however mandatory for cancelling the light of bright stars which will be partially resolved by future Extremely Large Telescopes in the near-infrared. In this paper, we first detail our motivations for developing an SGVC4 (charge 4) dedicated to the near-infrared domain. The challenge lies in the design of the pattern which is unrealistic in the theoretically perfect case, due to state-of-the-art manufacturing limitations. Hence, we propose a new realistic design of SGVC4 with minimized discontinuities and optimized phase ramp, showing conclusive improvements over previous works in this field. A preliminary validation of our concept is given based on RCWA simulations, while full 3D finite-difference time-domain simulations (and eventually laboratory tests) will be required for a final validation.

Place, publisher, year, edition, pages
2014. Vol. 9147, 91478Y
, Proceedings of SPIE, ISSN 0277-786X
Keyword [en]
extrasolar planet, vector vortex coronagraphy, phase mask, subwavelength grating, high contrast imaging, small inner working angle
National Category
Astronomy, Astrophysics and Cosmology Engineering and Technology
URN: urn:nbn:se:uu:diva-257487DOI: 10.1117/12.2055798ISI: 000354527800273ISBN: 978-0-8194-9615-7OAI: oai:DiVA.org:uu-257487DiVA: diva2:846403
5th Conference on Ground-Based and Airborne Instrumentation for Astronomy, JUN 22-26, 2014, Montreal, CANADA
Available from: 2015-08-17 Created: 2015-07-02 Last updated: 2015-11-11Bibliographically approved

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Forsberg, PontusKarlsson, Mikael
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