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 x 10^-6 at 3 lambda/D and 6 x 10^-7 at 10 lambda/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.