Band-limited image plane masks for the Terrestrial Planet Finder coronagraph: materials and designs for broadband performance.

Coronagraphs for detection and characterization of exosolar earthlike planets require accurate masks with broadband performance in the visible and near infrared spectrum. Design and fabrication of image plane masks capable of suppressing broadband starlight to 10(-10) level contrast presents technical challenges. We discuss basic approaches, material choices, designs, and fabrication options for image plane masks with particular focus on material properties to obtain adequate spectral performance. Based on theoretical analysis, we show that metals such as Pt and Ni, and alloys such as Inconel, may be employed as promising mask materials that can meet broadband performance requirements.