An Eight-Octant Phase-Mask Coronagraph

We present numerical simulations and laboratory experiments on an eight-octant phase-mask (EOPM) coronagraph. The numerical simulations suggest that an achievable contrast for the EOPM coronagraph can be greatly improved as compared to that of a four-quadrant phase-mask (FQPM) coronagraph for a partially resolved star. On-sky transmission maps reveal that the EOPM coronagraph has relatively high optical throughput, a small inner working angle, and large discovery space. We have manufactured an eight-segment phase mask utilizing a nematic liquid-crystal device, which can be easily switched between the FQPM and the EOPM modes. The la- boratory experiments demonstrate that the EOPM coronagraph has a better tolerance of the tip-tilt error than the FQPM one. We also discuss feasibility of a fully achromatic and high-throughput EOPM coronagraph utilizing a polarization interferometric technique.

[1]  L. Abe,et al.  Removal of central obscuration and spider arm effects with beam-shaping coronagraphy , 2006 .

[2]  Naoshi Baba,et al.  Combination of nulling interferometer and modified pupil for observations of exo-planets , 2005 .

[3]  Motohide Tamura,et al.  Nulling and adaptive optics for very high dynamic range coronagraph , 2006, SPIE Astronomical Telescopes + Instrumentation.

[4]  W. Traub,et al.  A laboratory demonstration of the capability to image an Earth-like extrasolar planet , 2007, Nature.

[5]  T. Kurokawa,et al.  Achromatic characteristics in 3-D Sagnac interferometer based on geometric phase shift , 2008, 2008 Conference on Lasers and Electro-Optics and 2008 Conference on Quantum Electronics and Laser Science.

[6]  D. Mawet,et al.  Coronagraphic imaging of three weak-line T Tauri stars: evidence of planetary formation around PDS 70 , 2006 .

[7]  Pierre Baudoz,et al.  The four-quadrant phase-mask coronagraph : white light laboratory results with an achromatic device , 2006 .

[8]  T. Kurokawa,et al.  Precise wavefront correction with unbalanced nulling interferometer for direct detection of exo-planet , 2007, 2007 Conference on Lasers and Electro-Optics - Pacific Rim.

[9]  Damien Gratadour,et al.  Four quadrant phase mask K -band coronagraphy of NGC 1068 with NAOS-CONICA at VLT , 2005 .

[10]  J. Nishikawa,et al.  Precise wavefront correction with an unbalanced nulling interferometer for exo-planet imaging coronagraphs , 2008, 0806.2026.

[11]  Mitsuo Takeda,et al.  Common-path achromatic interferometer-coronagraph: images from a breadboard demonstrator. , 2007, Applied optics.

[12]  Tsuyoshi Ishigaki,et al.  Polarization interferometric stellar coronagraph. , 2002, Optics letters.