Graded coronagraphic masks for high-contrast near-infrared imaging

摘要

We present here results from an experimental and theoretical study in the use of graded focal-plane occulting masks to improve high-contrast astronomical imaging at near-infrared wavelengths. The study includes investigations of both high-energy beam sensitive (HEBS) glass (a product of Canyon Materials, San Diego, CA) and binary notch-filter technologies to create precision graded occulting masks. In conjunction with this investigation, we conduct computer simulations showing expected high-contrast levels for various graded masks being considered for installation in the PHARO camera of the Palomar 200-inch (5m) Hale Telescope Adaptive Optics (AO) system. Our results demonstrate that the implementation of a graded exponential mask in the Palomar system should improve high-contrast sensitivities by about 2.4-mag in K-band (2.0-2.4 μm), for 0.75-1.5 arcsec separations. We also demonstrate that both HEBS and binary notch-filter technologies present adequate platforms for necessary occulting requirements. We conclude with a discussion of theinsights our study yields for planned space-based high-contrast observatories such as NASA's planned Terrestrial Planet Finder Coronagraph (TPF-C) and the proposed Eclipse mission.