Extreme coronagraphy for detecting exo-Earths

Abstract
The extreme cleaning of stellar images, needed for distinguishing their planets and especially those analogous to the Earth, requires coronagraphy and apodization. These techniques suppress the diffraction rings, but not the residual speckles resulting from the bumpiness of the optical surfaces. Several methods, coherent and incoherent, can in principle remove these speckles, but some of them are affected if the star is slightly resolved. With the future large hypertelescopes, spanning 100 kilometers or more to resolve the details of exo-Earths, this could require cleaning procedures applied separately for each sub-aperture before recombining the beams.