Monochromatic verification of high-contrast imaging with an occulter

Abstract

One of the most promising concepts of starlight suppression for direct imaging of exoplanets is flying a specially-shaped external occulter in formation with a space telescope. Here we present contrast performance verification of an occulter design scaled to laboratory-size using Fresnel numbers corresponding to the space design. Experimental design innovations include usage of an expanding beam to minimize phase aberrations, and an outer ring to minimize hard-edge diffraction effects. The apodizing performance of the optimized occulter edge is compared with a baseline case of a circular occulter and shown to result in contrast improvements. Experimental results in red monochromatic light show that the achieved laboratory contrast exceeds ten orders of magnitude, but with differences from the theoretical diffraction analysis limited by specular reflection from the mask edges.