The multistage and ring-apodized vortex coronagraph: two simple, small-angle coronagraphic solutions for heavily obscured apertures

Here we present two simple concepts to make the vortex coronagraph (VC) immune to heavily obscured apertures. The multi-stage VC (MSVC) uses the ability of the vortex to move light in and out of apertures through multiple VC in series to restore the nominal attenuation capability of the charge 2 vortex regardless of the aperture obscurations. The ring-apodized VC (RAVC) is a one-stage apodizer exploiting the VC Lyot-plane amplitude distribution in order to perfectly null the diffraction from any central obscuration size, and for any vortex topological charge. In this paper, we also emphasize the complementarity and similarities of the RAVC to the recently proposed Active Compensation of Aperture Discontinuities (ACAD, L. Pueyo et al. 2013, these proceedings) and more finely optimized shaped-pupil-like apodizations (A. Carlotti et al. 2013, these proceedings). This paper ends with a brief discussion about the trade-offs these techniques offer in the framework of the Extremely Large Telescopes (ELT) and the Astrophysics Focused Telescope Assets (AFTA).