Laboratory Testing of a Lyot Coronagraph Equipped with an Eighth-Order Notch Filter Image Mask

We have built a series of notch filter image masks that make the Lyot coronagraph less susceptible to low spatial frequency optical aberrations. In this paper we present experimental results of their performance in the lab using monochromatic light. Our tests show that these "eighth-order" masks are resistant to tilt and focus alignment errors and can generate contrast levels of 2 × 10-6 at 3λ/D and 6 × 10-7 at 10λ/D without the use of corrective optics such as deformable mirrors. This work supports recent theoretical studies suggesting that eighth-order masks can provide the Terrestrial Planet Finder-Coronagraph with a large search area, high off-axis throughput, and a practical requisite pointing accuracy.