Complex apodization Lyot coronagraphy for the direct imaging of exoplanet systems: design, fabrication, and laboratory demonstration

We review the design, fabrication, performance, and future prospects for a complex apodized Lyot coronagraph for highcontrast exoplanet imaging and spectroscopy. We present a newly designed circular focal plane mask with an inner working angle of 2.5 λ/D. Thickness-profiled metallic and dielectric films superimposed on a glass substrate provide control over both the real and imaginary parts of the coronagraph wavefront. Together with a deformable mirror for control of wavefront phase, the complex Lyot coronagraph potentially exceeds billion-to-one contrast over dark fields extending to within angular separations of 2.5 λ/D from the central star, over spectral bandwidths of 20% or more, and with throughput efficiencies better than 50%. Our approach is demonstrated with a linear occulting mask, for which we report our best laboratory imaging contrast achieved to date. Raw image contrasts of 3×10^(-10) over 2% bandwidths, 6×10^(-10) over 10% bandwidths, and 2×10^(-9) over 20% bandwidths are consistently 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 experiments and optical models, and prospects for further progress are summarized. The science capability of the hybrid Lyot coronagraph is compared with requirements for ACCESS, a representative space coronagraph concept for the direct imaging and spectroscopy of exoplanet systems. This work has been supported by NASA’s Strategic Astrophysics Technology / Technology Demonstrations for Exoplanet Missions (SAT/TDEM) program.