Occulting Focal Plane Masks for Terrestrial Planet Finder Coronagraph: Design, Fabrication, Simulations and Test Results

Abstract

Occulting focal plane masks for the Terrestrial Planet Finder Coronagraph (TPF-C) could be designed with continuous gray scale profile of the occulting pattern such as 1 − sinc 2 on a suitable material or with micron-scale binary transparent and opaque structures of metallic pattern on glass. We have designed, fabricated and tested both kinds of masks. The fundamental characteristics of such masks and initial test results from the High Contrast Imaging Test bed (HCIT) at JPL are presented.

Band-limited masks for TPF coronagraph

“…Both HEBS and binary masks were mounted side by side to facilitate the use of either mask by external control without breaking vacuum and to ensure nearly identical conditions for the two masks during the tests. [8], we obtained C m ∼ 9 × 10 −10 with a stability of about 0.5 × 10 −10 per hour. In a more detailed study [15] conducted in 2006, we obtained C m ∼ 6 × 10 −10 in a nulling window defined by a 'D' shaped region covering 4 to 10 λ/D.…”

“…'Continuous' and 'sampled' sin 2 and 1 − sinc 2 type masks as shown in Fig. 3 have been designed and fabricated [8].…”

“…Fig. 4 shows a close-up view [8] of a fabricated 'continuous' 1 − sinc 2 type binary mask. It is designed to mimic the 1 − sinc 2 transmission profile of the HEBS mask.…”

“…Different types of these masks have been designed and fabricated for laboratory tests [8,9] at JPL as described below.…”

Detecting extra-solar planets with the Japanese 3.5 m SPICA space telescope

“…The masks were manufactured by Canyon Materials Inc. with the HEBS-glass technology [31]. Although some encouraging coronagraphic results were already obtained with HEBS-glass focal plane masks [32], the phase delay introduced by the HEBS-glass [33] turned out to be a very strong limitation to the experiment performance since we did not use adaptive control of the wavefront to compensate for it. These phase aberrations arise from the mask design itself which uses a refractive substrate.…”