21 September 2012 Coronagraph focal-plane phase masks based on photonic crystal technology: recent progress and observational strategy
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Photonic crystal, an artificial periodic nanostructure of refractive indices, is one of the attractive technologies for coronagraph focal-plane masks aiming at direct imaging and characterization of terrestrial extrasolar planets. We manufactured the eight-octant phase mask (8OPM) and the vector vortex coronagraph (VVC) mask very precisely using the photonic crystal technology. Fully achromatic phase-mask coronagraphs can be realized by applying appropriate polarization filters to the masks. We carried out laboratory experiments of the polarization-filtered 8OPM coronagraph using the High-Contrast Imaging Testbed (HCIT), a state-of-the-art coronagraph simulator at the Jet Propulsion Laboratory (JPL). We report the experimental results of 10-8-level contrast across several wavelengths over 10% bandwidth around 800nm. In addition, we present future prospects and observational strategy for the photonic-crystal mask coronagraphs combined with differential imaging techniques to reach higher contrast. We proposed to apply the polarization-differential imaging (PDI) technique to the VVC, in which we built a two-channel coronagraph using polarizing beam splitters to avoid a loss of intensity due to the polarization filters. We also proposed to apply the angular-differential imaging (ADI) technique to the 8OPM coronagraph. The 8OPM/ADI mode mitigates an intensity loss due to a phase transition of the mask and provides a full field of view around central stars. We present results of preliminary laboratory demonstrations of the PDI and ADI observational modes with the phase-mask coronagraphs.
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Naoshi Murakami, Naoshi Murakami, Jun Nishikawa, Jun Nishikawa, Wesley A. Traub, Wesley A. Traub, Dimitri Mawet, Dimitri Mawet, Dwight C. Moody, Dwight C. Moody, Brian D. Kern, Brian D. Kern, John T. Trauger, John T. Trauger, Eugene Serabyn, Eugene Serabyn, Shoki Hamaguchi, Shoki Hamaguchi, Fumika Oshiyama, Fumika Oshiyama, Moritsugu Sakamoto, Moritsugu Sakamoto, Akitoshi Ise, Akitoshi Ise, Kazuhiko Oka, Kazuhiko Oka, Naoshi Baba, Naoshi Baba, Hiroshi Murakami, Hiroshi Murakami, Motohide Tamura, Motohide Tamura, } "Coronagraph focal-plane phase masks based on photonic crystal technology: recent progress and observational strategy", Proc. SPIE 8442, Space Telescopes and Instrumentation 2012: Optical, Infrared, and Millimeter Wave, 844205 (21 September 2012); doi: 10.1117/12.925613; https://doi.org/10.1117/12.925613

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