EDP Sciences
Free access
Volume 477, Number 1, January I 2008
Page(s) 329 - 335
Section Astronomical instrumentation
DOI http://dx.doi.org/10.1051/0004-6361:20078270

A&A 477, 329-335 (2008)
DOI: 10.1051/0004-6361:20078270

Interferometric apodization of telescope apertures

I. First laboratory results obtained using a Mach-Zehnder interferometer
A. Carlotti1, G. Ricort1, C. Aime1, Y. El Azhari2, and R. Soummer3

1  Laboratoire Universitaire d'Astrophysique de Nice (LUAN), Université de Nice Sophia-Antipolis, Parc Valrose, 06108 Nice, France
    e-mail: [Alexis.Carlotti;Gilbert.Ricort;Claude.Aime]@unice.fr
2  Laboratoire de Physique des Hautes Énergies et Astrophysique, Département de Physique, Faculté des Sciences Semlalia, Université Cadi Ayyad, BP 2390, Marrakech, Morocco
    e-mail: elazhari@ucam.ac.ma
3  American Museum of Natural History (AMNH), 79th Street at Central Park West, New York, NY 10024, USA
    e-mail: rsoummer@amnh.org

(Received 13 July 2007 / Accepted 17 September 2007)

Aims.We seek to produce apodized apertures for application in stellar coronagraphy to help in direct detections of exoplanets. We show that chromatic apodized apertures of any shape in transmission can be obtained with a specific MZI and we demonstrate this capability in two cases.
Methods.The method takes advantage of the capabilities of the MZI, in which the two outputs correspond to the addition and subtraction of the two wave amplitudes in both arms. The result is obtained by re-imaging the entrance aperture of the telescope in the arms of the MZI where two complementary phase masks $\pm$ $\varphi (x,y)$ are set. At the two outputs of the MZI, the re-imaged apertures interfere, and their transmissions are multiplied respectively by a factor of the form $ \cos[\varphi(x,y)]$ and $i \sin[\varphi(x,y)]$. They correspond to the apodized and anti-apodized complementary outputs.
Results.We present the results obtained for two types of apodization. A 1D cosine apodization for a square aperture is obtained by introducing a thin wedge-shaped air film, slightly tilting one of the mirrors of the MZI. A 2D circular symmetric apodization of the form $\cos[x^{2}+y^{2}]$ is obtained for a circular aperture using two complementary convergent and divergent lenses as phase masks. Aperture transmissions (in intensity) and corresponding point spread functions (PSFs) are given in each case and compared to the theoretical expectations.
Conclusions.We have demonstrated the capability of the MZI to produce an apodized aperture. This result is obtained with no loss of photons, considering the fact that there are two complementary outputs. Considerations are given on the wavelength dependence of this technique.

Key words: instrumentation: high angular resolution -- methods: laboratory -- techniques: interferometric

© ESO 2007