Issue |
A&A
Volume 504, Number 2, September III 2009
|
|
---|---|---|
Page(s) | 663 - 671 | |
Section | Astronomical instrumentation | |
DOI | https://doi.org/10.1051/0004-6361/200912067 | |
Published online | 09 July 2009 |
Phase mask coronagraphy using a Mach-Zehnder interferometer
Université de Nice Sophia-Antipolis, Centre National de la Recherche Scientifique, Laboratoire Fizeau, Observatoire de la Côte d'Azur, Parc Valrose, 06108 Nice Cedex, France e-mail: [alexis.carlotti;gilbert.ricort;claude.aime]@unice.fr
Received:
13
March
2009
Accepted:
9
June
2009
Aims. We report results obtained with a four-quadrant and an eight-octant phase-mask coronagraphs (4QC and 8OC) produced using amplitude masks inside a Mach-Zehnder interferometer (MZI). We describe the laboratory implementation of these coronagraphs operated in laser light and provide a detailed comparison between theory and experiment.
Methods. The +1 and –1 (π phase) amplitude transmissions required to produce a 4QC or an 8OC were obtained using complementary binary-masks (transmission of 1 or 0 for quadrants of similar parities) in the two arms of a MZI, taking advantage of the achromatic π phase shift between the two paths. In one output of the MZI, the reconstructed image of the focal plane is similar to those obtained for sectorised phase-masks coronagraphs, and the image of the aperture corresponds to the characteristic patterns of the 4QC/8OC coronagraphs.
Results. Observations are compared with the theory published by other
authors and developed further here. The expressions for the light
diffracted outside the aperture image are simplified using the
Zernike radial polynomials instead of the
rapidly diverging hypergeometric functions otherwise used.
Experimental results are found to be in very good agreement with the
theory. With the present laboratory experiment, about 99% of the
light is rejected outside the Lyot stop and the contrast obtained
beyond
is higher than 105 for both the 4QC and
8OC. As expected, the 8OC is less affected by a pointing
error than the 4QC, but more sensitive to an aperture central
obstruction. Incidently, the loss of transmission for a planet
crossing two phase masks is given theoretically as a function of
the Lyot stop size, in agreement with observations.
Key words: instrumentation: high angular resolution / methods: laboratory / techniques: high angular resolution / techniques: interferometric
© ESO, 2009
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