A hybrid Lyot coronagraph for the direct imaging and spectroscopy of exoplanet systems: recent results and prospects

We report our best laboratory contrast demonstrations achieved to date. We review the design, fabrication, performance, and future prospects of a hybrid focal plane occulter for exoplanet coronagraphy. Composed of thickness-profiled metallic and dielectric thin films vacuum deposited on a fused silica substrate, the hybrid occulter uses two superimposed thin films for control over both the real and imaginary parts of the complex attenuation pattern. Together with a deformable mirror for adjustment of wavefront phase, the hybrid Lyot coronagraph potentially exceeds billion-toone contrast over dark fields extending to within angular separations of 3 λ/D from the central star, over spectral bandwidths of 20% or more, and with throughput efficiencies up to 60%. We report laboratory contrasts of 3×10-10 over 2% bandwidths, 6×10-10 over 10% bandwidths, and 2×10-9 over 20% bandwidths, achieved across high contrast fields extending from an inner working angle of 3 λ/D to a radius of 15 λ/D. Occulter performance is analyzed in light of recent experiments and optical models, and prospects for further improvements are summarized. The science capabilities of the hybrid Lyot coronagraph are compared with requirements of the ACCESS mission, a representative exoplanet space telescope concept study for the direct imaging and spectroscopy of exoplanet systems. This work has been supported by NASA's Technology Demonstration for Exoplanet Missions (TDEM) program.