High Contrast Imaging with Gaussian Aperture Pupil Masks

Abstract

Gaussian aperture pupil masks (GAPMs) can in theory achieve the contrast requisite for directly imaging an extrasolar planet. We outline the process of fabricating and testing a GAPM for use on the Penn State near-IR Imager and Spectrograph (PIRIS) at the Mt. Wilson 100$^{\prime\prime}$ telescope. We find that the initial prototype observations are quite successful, achieving a contrast similar to a traditional Lyot coronagraph witho ut blocking any light from a central object and useful for finding faint companions to nearby young solar analogues. In the lab we can reproduce the expected PSF to within an order of magnitude and with new designs achieve $\sim5 \times 10^{-5}$ contrast at 10$λ/D$. We find that small inaccuracies in the mask fabrication process and insufficient correction of the atmosphere contribute the most degradation to contrast. Finally we compare the performance of GAPMs and Lyot coronagraphs of similar throughput.