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28 August 2014 Adaptive optics operation with focal wavefront sensor in a coronagraph for direct observation of exoplanets
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A stellar coronagraph system for direct observations of extra solar planets is under development by combining unbalanced nulling interferometer (UNI), adaptive optics, and a focal plane mask coronagraph1,2,3,4,5,6. It can reach a high contrast as using λ/10000 precision optics by λ/1000 quality ones. However, a sufficient high contrast is not obtained yet in the experiment before. It is thought that the remained speckle noise at the final coronagraph focal plane detector are produced by a “non-common path error” of λ/100 level, which is a wavefront error of the coronagraph different from that of a wavefront sensor (WFS) of adaptive optics, even when the WFS indicates λ/1000 conversion. The non-common path error can be removed by the dark zone method that is the way of wavefront correction by wavefront sensing at the final focal plane detector, although it has an issue of operation for very faint targets because of a slow feedback loop. In the present paper, we describe that our coronagraph system becomes practically higher contrast by upgrading the control method of deformable mirror (DM) with the WFS assisted by final focal plane wavefront sensing method. We accomplished contrast of 8×10-7 relative to the star in experiment.
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Masahito Oya, Jun Nishikawa, Masaaki Horie, Kazuma Sato, Masao Fukase, Naoshi Murakami, Takayuki Kotani, Shiomi Kumagai, Motohide Tamura, Yosuke Tanaka, and Takashi Kurokawa "Adaptive optics operation with focal wavefront sensor in a coronagraph for direct observation of exoplanets", Proc. SPIE 9143, Space Telescopes and Instrumentation 2014: Optical, Infrared, and Millimeter Wave, 91433B (28 August 2014);

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