Performance results of the TFI coronagraphic occulting maskprototypes

摘要

The JWST Fine Guidance Sensor (FGS) Tunable Filter Imager (TFI) will feature a coronagraph for high contrast imaging applications. TFI will provide unique narrow-band imaging and coronagraphic capabilities impacting the detection of "First Light", i.e. stellar systems formed just after the Big Bang, and the detection and characterization of exoplanets. The TFI coronagraph is made of a set of four occulting spots and four Lyot stops. The TFI focal-plane masks under consideration are apodized (Gaussian profile) or hard masks. The masks are operating in reflection and implemented as small cones directly engraved on the pick-off mirror located at the telescope focus. This paper presents laboratory performance of two prototype masks (hard and Gaussian masks). The hard mask results are in good agreement with the expected performance of a standard Lyot coronagraph. On the other hand, the halftone mask shows significant departure from theoretical expectation; these results could be due to diffraction effects within the halftone mask.