Three years in metasurface development for exoplanet imaging at UC Santa Barbara

As ideas for next-generation vortex coronagraphic phase masks mature, real-world implementations have begun to take shape. We describe new metasurface scalar vortex designs for visible wavelengths. By combining two metasurfaces together to achieve achromatic 2π phase control, we demonstrate simulated phase residuals 90% with easy-to-manufacture nanopost geometry. Such designs rival the deepest broadband simulated direct imaging contrasts achieved by a scalar vortex and can readily be fabricated and tested. The combined metasurface technique may aid the pursuit of a vortex phase mask that meets the demands of the proposed Habitable Worlds Observatory. Concurrent with these efforts, we detail preparations for the installation of a metasurface vortex in the NIRC2 instrument at Keck Observatory. Such preparations include fabrication, characterization and the construction of a new coronagraph testbed. We report on first-light results from this testbed, with our metasurface achieving starlight rejection of ~10^-2 over 10% bandwidth.