Removal of coronagraphy residues with an adaptive hologram, for imaging exo-Earths

Abstract
Exo-planets much fainter than their parent star are likely imageable at visible wavelengths with a 2 to 8 meter space telescope equipped for coronagraphy. The dynamic range can be further increased by nulling the speckled star residue, before detection, with an adaptive hologram. Like the Mach-Zehnder interferometer of Codona & Angel (2004), the hologram subtracts from the stellar residue. a copy of it, made with the light rejected by the Lyot mask. The final residue can in principle be as low as one photon per speckle, on average. It makes exo-Earths detectable if their Airy peak contains a few photons. The method can also relax the difficult figuring tolerances for the pre-focal optics. With Lippmann-Bragg holograms, it can be achromatized.