Article (Scientific journals)
Parasitic interference in nulling interferometry
Matter, A.; Defrere, Denis; Danchi, W. C. et al.
2013In Monthly Notices of the Royal Astronomical Society, 431 (2), p. 1286-1295
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Keywords :
instrumentation: interferometers; methods: analytical; techniques: interferometric
Abstract :
[en] Nulling interferometry aims to detect faint objects close to bright stars. Its principle is to produce a destructive interference along the line of sight so that the stellar flux is rejected, while the flux of the off-axis source can be transmitted. In practice, various instrumental perturbations can degrade the nulling performance. Any imperfection in phase, amplitude or polarization produces a spurious flux that leaks to the interferometer output and corrupts the transmitted off-axis flux. One of these instrumental perturbations is the crosstalk phenomenon, which occurs because of multiple parasitic reflections inside transmitting optics, and/or diffraction effects related to beam propagation along finite size optics. It can include a crosstalk of a beam with itself, and a mutual crosstalk between different beams. This can create a parasitic interference pattern, which degrades the intrinsic transmission map - or intensity response - of the interferometer. In this context, we describe how this instrumental effect impairs the performance of a Bracewell interferometer. A simple formalism is developed to derive the corresponding modified intensity response of the interferometer, as a function of the two parameters of interest: the crosstalk level (or contamination rate) and the phase shift between the primary and secondary - parasitic - beams. We then apply our mathematical approach to a few scientific cases, both analytically and using the GENIESIM simulation software, adapted to handle coherent crosstalk. Our results show that a coherent crosstalk level of about 1 per cent implies a 20 per cent drop of the signal-to-noise ratio at most. Careful attention should thus be paid to reduce the crosstalk level inside an interferometric instrument and ensure an instrumental stability that provides the necessary sensitivity through calibration procedures.
Disciplines :
Space science, astronomy & astrophysics
Author, co-author :
Matter, A.;  Max Planck Institut für Radioastronomie, auf dem Hügel, 69, D-53121 Bonn, Germany
Defrere, Denis ;  Max Planck Institut für Radioastronomie, auf dem Hügel, 69, D-53121 Bonn, Germany ; Steward Observatory, Department of Astronomy, University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
Danchi, W. C.;  NASA/GSFC, Greenbelt, MD 20771, USA
Lopez, B.;  Laboratoire Lagrange, CNRS UMR 7293, UNS - Observatoire de la Côte d'Azur BP 4229, F-06304 Nice Cedex 4, France
Absil, Olivier  ;  Université de Liège - ULiège > Département d'astrophys., géophysique et océanographie (AGO) > Astroph. extragalactique et observations spatiales (AEOS)
Language :
English
Title :
Parasitic interference in nulling interferometry
Publication date :
11 May 2013
Journal title :
Monthly Notices of the Royal Astronomical Society
ISSN :
0035-8711
eISSN :
1365-2966
Publisher :
Blackwell Publishing, Oxford, United Kingdom
Volume :
431
Issue :
2
Pages :
1286-1295
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 15 April 2013

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