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Laboratory demonstration of a mid-infrared AGPM vector vortex coronagraph
Hololab, Université de Liège.
IAGL, Université de Liège.
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Microsystems Technology.
European Southern Observatory.
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2013 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 553, A98- p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
2013. Vol. 553, A98- p.
Keyword [en]
coronagraph diamond
National Category
Astronomy, Astrophysics and Cosmology Engineering and Technology
Research subject
Engineering Science with specialization in Microsystems Technology
URN: urn:nbn:se:uu:diva-192563DOI: 10.1051/0004-6361/201321126ISI: 000319858700098OAI: diva2:599978
Available from: 2013-01-22 Created: 2013-01-22 Last updated: 2014-02-03Bibliographically approved
In thesis
1. Diamond Microfabrication for Applications in Optics and Chemical Sensing
Open this publication in new window or tab >>Diamond Microfabrication for Applications in Optics and Chemical Sensing
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Diamond is a material with many exceptional properties. In this thesis methods for fabrication of microstructures as well as several applications of such structures in optics, microfluidics and electrochemistry are presented.

A method for etching deep and highly precise gratings is described. This method was used to fabricate circularly symmetric half wave plates for use in vector vortex coronagraphs. Such coronagraphs are a very promising approach to the direct imaging of extrasolar planets.

By varying the lateral etch rate of the aluminum mask during diamond etching in an inductively coupled plasma, the sidewall angle of the etched structures could be controlled. This method was used to make smooth sloped sides on a waveguide for coupling light into it. Antireflective structures that drastically reduced the surface reflection in a wavelength band between 10 and 50 µm were also fabricated.

An array of boron doped diamond microelectrodes for electrochemical measurements in a microchannel was fabricated and tested, showing very good stability and reusability. Several hundred hours of use did not adversely affect their performance and no damage to them could be detected by atomic force microscopy or scanning electron microscopy.

Superhydrophobic surfaces in diamond were demonstrated, using both hydrogen and fluorine termination. Hydrogen termination on a flat surface gives contact angles below 90°. To achieve a superhydrophobic surface with this low intrinsic hydrophobicity, structures looking like microscopic nail heads were fabricated. The effect of water pressure on immersed superhydrophobic surfaces was also studied and it was found that the collapse of the superhydrophobic state due to pressure was sometimes reversible as the pressure was lowered.

Finally, a method was tested for functionalizing diamond surfaces using block copolymers of polyethylene oxide and polypropylene oxide to both passivate the surface and to attach synthetic binder molecules. This method was found to give very high signal to noise ratios when detecting C-reactive protein.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2013. 65 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1015
diamond, microfabrication, microoptics, coronagraph, waveguide, microelectrodes, superhydrophobic
National Category
Manufacturing, Surface and Joining Technology Astronomy, Astrophysics and Cosmology
Research subject
Engineering Science with specialization in Microsystems Technology
urn:nbn:se:uu:diva-192567 (URN)978-91-554-8587-0 (ISBN)
Public defence
2013-03-08, Polacksbacken 2347, Lägerhyddsvägen 2, Uppsala, 10:00 (English)
Available from: 2013-02-14 Created: 2013-01-22 Last updated: 2013-04-02

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