  The Telescope for Habitable Exoplanets and Interstellar/Intergalactic
Astronomy (THEIA) is a mission concept study for a flagship-class
telescope-occulter system to search for terrestrial planets and perform general
astrophysics with a space-based 4m telescope. A number of design options were
considered for the occulter and telescope optical systems; in this paper we
discuss the design of occulters and coronagraphs for THEIA and examine their
merits. We present two optimized occulters: a 25.6m-radius occulter with 19m
petals that achieves 10^-12 suppression from 250-1000nm with a 75mas inner
working angle, and a 20.0m-radius occulter with 10m petals that achieves 10^-12
suppression from 250-700nm with a 75mas inner working angle. For more widely
separated planets (IWA > 108mas), this second occulter is designed to operate
at a second closer distance where it provides 10^-12 suppression from
700-1000nm. We have also explored occulter/coronagraph hybrid systems, and
found that an AIC coronagraph that exploits the symmetry of the PSF at the
occulter can improve performance; however, it requires very accurate tolerances
on the occulter manufacturing of the telescope/occulter system as the AIC does
not cancel asymmetric terms. Other coronagraphs proved infeasible, primarily
due to the fact that the residual starlight from the occulter is not a plane
wave, and so is poorly suppressed by the coronagraph.
