Issue EAS Publications Series Volume 8, 2003 Astronomy with High Contrast Imaging Page(s) 117 - 128 DOI 10.1051/eas:2003056

Astronomy with High Contrast Imaging
C. Aime and R. Soummer (eds)
EAS Publications Series, Vol. 8, 2003
DOI: 10.1051/eas:2003056

Achromatic Four Quadrant Phase Mask Coronagraph using the Dispersion of Form Birefringence

D. Mawet¹, C. Lenaerts², V. Moreau², Y. Renotte², D. Rouan³ and J. Surdej<sup>1

1</sup>  IAGL, Université de Liège, 17, B5C Allée du 6 Août, 4000 Sart Tilman, Belgium
²  HOLOLAB, Université de Liège, 17, B5 Allée du 6 Août, 4000 Sart Tilman, Belgium
³  DESPA, Observatoire de Paris-Meudon, 5 Pl. J. Janssen, 92195 Meudon, France

Abstract
We describe an alternative design for the 4-quadrant phase mask coronagraph described recently by Rouan et al. (2000). Based on the same principle, i.e. producing a very efficient nulling by mutually destructive interferences of the coherent light from the main source, our mask realises the  phase shift using some properties of ZOGs (Zeroth Order Gratings) and according to an original scheme respecting the 4-quadrant symmetry. When the period of the one-dimension grating structure is smaller than the wavelength of the incident light, the structure becomes birefringent. The effective refractive indices depend on the wavelength. Using this feature, we can design a mask whose nulling efficiency is maintained within a wide wavelength range. Numerical simulations were made according to the RCWA (Rigorous Coupled Wave Analyses).

© EAS, EDP Sciences 2003

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