28 August 2014 Recent progress on phase-mask coronagraphy based on photonic-crystal technology
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We have been developing focal-plane phase-mask coronagraphs ultimately aiming at direct detection and characterization of Earth-like extrasolar planets by future space coronagraph missions. By utilizing photonic-crystal technology, we manufactured various coronagraphic phase masks such as eight-octant phase masks (8OPMs), 2nd-order vector vortex masks, and a 4th-order discrete (32-sector) vector vortex mask. Our laboratory experiments show that the 4th-order vortex mask reaches to higher contrast than the 2nd-order one at inner region on a focal plane. These results demonstrate that the higher-order vortex mask is tolerant of low-order phase aberrations such as tip-tilt errors. We also carried out laboratory demonstration of the 2nd-order vector vortex masks in the High-Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory (JPL), and obtained 10-8-level contrast owing to an adaptive optics system for creating dark holes. In addition, we manufactured a polarization-filtered 8OPM, which theoretically realizes achromatic performance. We tested the manufactured polarization-filtered 8OPM in the Infrared Coronagraphic Testbed (IRCT) at the JPL. Polychromatic light sources are used for evaluating the achromatic performance. The results suggest that 10-5- level peak-to-peak contrasts would be obtained over a wavelength range of 800-900 nm. For installing the focal-plane phase-mask coronagraph into a conventional centrally-obscured telescope with a secondary mirror, pupil-remapping plates have been manufactured for removing the central obscuration to enhance the coronagraphic performance. A result of preliminary laboratory demonstration of the pupil-remapping plates is also reported. In this paper, we present our recent activities of the photonic-crystal phase coronagraphic masks and related techniques for the high-contrast imaging.
© (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Naoshi Murakami, Jun Nishikawa, Motohide Tamura, Eugene Serabyn, Wesley A. Traub, Kurt M. Liewer, Dwight C. Moody, John T. Trauger, Olivier Guyon, Frantz Martinache, Nemanja Jovanovic, Garima Singh, Fumika Oshiyama, Hayato Shoji, Moritsugu Sakamoto, Shoki Hamaguchi, Kazuhiko Oka, Naoshi Baba, "Recent progress on phase-mask coronagraphy based on photonic-crystal technology", Proc. SPIE 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 914334 (28 August 2014); doi: 10.1117/12.2054790; https://doi.org/10.1117/12.2054790


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