Multiple-stage apodized pupil Lyot coronagraph for high-contrast imaging

We describe the multiple-stage Lyot coronagraph first proposed by Aime, Soummer and Ferrari (A&A 2002, 389,334344) for the detection of exoplanets. This coronagraph uses several stages. The first stage is a Prolate Apodized Lyot Coronagraph (PALC). It produces a residual wavefront on the aperture that is proportional to the entrance prolate spheroidal apodized wavefront. This permits the use of a second stage of coronagraphy, needing only a Lyot mask, identical to the first one, without any further aperture apodization. The resulting extinction factor is the square of the initial PALC. Using several stages permits to obtain considerable rejection factors for small-size coronagraphic masks and good overall throughput.