Achromatic dual-zone phase mask stellar coronagraph

This paper presents a generalization of the Roddier & Roddier Phase Mask coronagraph for polychromatic observations. It is shown that using a dual-zone phase mask, combined with complex apodization, both phase and size chromatism can be compensated simultaneously to produce high extinction of a point source over large bandwidths, for example the entire K band with a residual integrated starlight of 3.2 x 10(-4) and a star intensity level of 10(-6) at an angular separation of 3lambda/D. Other advantages of the proposed technique include the compatibility with centrally obscured telescopes, absence of blind axes and no symmetrization of the images.