http://arxiv.org/abs/2210.09412
The number of terrestrial exoplanets accessible to high-contrast coronagraphic imaging with large telescopes is limited by the smallest angular offset from bright stars at which coronagraphs can observe. However, it is possible to reach inside a telescopes coronagraphic regime by employing nulling interferometry across a telescopes pupil. Indeed, cross-aperture nulling interferometry can observe significantly closer to stars than typical coronagraphs, enabling observations even within the stellar diffraction core. Identifying an optimal nulling coronagraph, i.e., one with both a very small IWA and a high throughput for exoplanet light, would thus be of great interest. A systematic examination of available nulling options has therefore been carried out, which has led to three things. The first is a topological overview that unites both multi-aperture nulling interferometers and single-aperture phase coronagraphs into a common geometrical framework. The second is a new type of phase-mask coronagraph that has emerged from a gap in this framework, called here the split-ring coronagraph. The third is a clear identification of the optimal configuration for a nulling coronagraph, which turned out to be an aperture-plane phase knife, i.e., an achromatic pi-radian phase shift applied to half the telescope pupil prior to focusing the telescopes point spread function into a single-mode fiber. The theoretical peak efficiency of the phase-knife fiber coronagraph, 35.2 percent for a circular telescope aperture, is found to be almost twice that of the next most efficient case, the vortex fiber nuller, at 19.0 percent.
E. Serabyn, G. Ruane and D. Echeverri
Wed, 19 Oct 22
2/87
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