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Post-coronagraphic tip-tilt sensing for vortex phase masks: The QACITS technique

Huby, E. and Baudoz, P. and Mawet, D. and Absil, O. (2015) Post-coronagraphic tip-tilt sensing for vortex phase masks: The QACITS technique. Astronomy and Astrophysics, 584 . Art. No. A74. ISSN 0004-6361. doi:10.1051/0004-6361/201527102.

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Context. Small inner working angle coronagraphs, such as the vortex phase mask, are essential to exploit the full potential of ground-based telescopes in the context of exoplanet detection and characterization. However, the drawback of this attractive feature is a high sensitivity to pointing errors, which degrades the performance of the coronagraph. Aims. We propose a tip-tilt retrieval technique based on the analysis of the final coronagraphic image, hereafter called Quadrant Analysis of Coronagraphic Images for Tip-tilt Sensing (QACITS). Methods. Under the assumption of small phase aberrations, we show that the behavior of the vortex phase mask can be simply described from the entrance pupil to the Lyot stop plane with Zernike polynomials. This convenient formalism is used to establish the theoretical basis of the QACITS technique. We performed simulations to demonstrate the validity and limits of the technique, including the case of a centrally obstructed pupil. Results. The QACITS technique principle is validated with experimental results in the case of an unobstructed circular aperture, as well as simulations in presence of a central obstruction. The typical configuration of the Keck telescope (24% central obstruction) has been simulated with additional high order aberrations. In these conditions, our simulations show that the QACITS technique is still adapted to centrally obstructed pupils and performs tip-tilt retrieval with a precision of 5 × 10-2λ/D when wavefront errors amount to λ/ 14 rms and 10-2λ/D for λ/ 70 rms errors (with λ the wavelength and D the pupil diameter). Conclusions. We have developed and demonstrated a tip-tilt sensing technique for vortex coronagraphs. The implementation of the QACITS technique is based on the analysis of the scientific image and does not require any modification of the original setup. Current facilities equipped with a vortex phase mask can thus directly benefit from this technique to improve the contrast performance close to the axis.

Item Type:Article
Related URLs:
URLURL TypeDescription
Mawet, D.0000-0002-8895-4735
Absil, O.0000-0002-4006-6237
Additional Information:© ESO, 2015. Received 1 August 2015 / Accepted 10 September 2015. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programme (ERC Grant Agreement n. 337569) and from the French Community of Belgium through an ARC grant for Concerted Research Action.
Funding AgencyGrant Number
European Research Council (ERC)337569
Communauté française de Belgique – Actions de recherche concertéesUNSPECIFIED
Subject Keywords:techniques: high angular resolution / methods: analytical / methods: numerical
Record Number:CaltechAUTHORS:20160115-155025124
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Official Citation:Post-coronagraphic tip-tilt sensing for vortex phase masks: The QACITS technique E. Huby, P. Baudoz, D. MawetE. Huby, P. Baudoz, D. Mawet and O. Absil A&A, 584 (2015) A74 DOI:
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63727
Deposited By: George Porter
Deposited On:19 Jan 2016 19:19
Last Modified:10 Nov 2021 23:20

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