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A family of subwavelength grating vortexcoronagraphs (SGVCs) with higher topological charge
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Applied Materials Sciences.
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2015 (English)In: Techniques and Instrumentation for Detection of Exoplanets VII, 2015, Vol. 9605Conference paper, Oral presentation with published abstract (Refereed)
Abstract [en]

The subwavelength grating vortex coronagraph (SGVC) is a focal-planespiral-like phase mask whose key benefit is to allow high contrast imaging atsmall angles. Directly etched onto a CVD diamond substrate, it is well suitedto perform in the mid-infrared domain. It provides a continuous helicalphase ramp with a dark singularity in its center, and is characterized by itsnumber of phase revolutions, called the topological charge. Over the pasttwo years, we have manufactured several charge-2 SGVCs (a.k.a. annulargroove phase masks) and successfully demonstrated their performanceson 10-m class telescopes (LBT, VLT/NaCo, VLT/VISIR). To prevent stellarleakage on future 30-m class telescopes (E-ELT, TMT, GMT), a broaderoff-axis extinction is required, which can be achieved by increasing thetopological charge. We have recently proposed an original design for acharge-4 SGVC allowing less starlight to leak through the coronagraph, atthe cost of a degraded inner working angle. In this talk, we report on ourlatest development of higher charge SGVCs. From 3D rigorous numericalsimulations using a finite-difference time-domain (FDTD) algorithm, weConference 9605: Techniques and Instrumentationfor Detection of Exoplanets VIIR eturn to Contents +1 360 676 3290 · help@spie.org 647have derived a family of coronagraphs with higher topological charge(SGVC4/6/8). Our new optimization method addresses the principallimitation of such space-variant polarization state manipulation, i.e., theinconvenient discontinuities in the discrete grating pattern. The resultinggratings offer improved precision to the phase modulation compared toprevious designs. Finally, we present our preliminary manufacturing andmetrology results for infrared components down to the K-band.

Place, publisher, year, edition, pages
2015. Vol. 9605
Series
Proceedings of SPIE
National Category
Astronomy, Astrophysics and Cosmology Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-285236DOI: 10.1117/12.2218637OAI: oai:DiVA.org:uu-285236DiVA: diva2:921144
Conference
SPIE Optics + Photonics: Techniques and Instrumentation for Detection of Exoplanets VII, AUG 13-15, 2015, San Diego, USA
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2016-04-25

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Forsberg, PontusVargas Catalan, ErnestoKarlsson, Mikael

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