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20 July 2010 Testing of a transmission-filter coronagraph for ground-based imaging of exoplanets
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We present the latest laboratory test of a new coronagraph using one step-transmission filter at the visible wavelength. The primary goal of this work is to test the feasibility and stability of the coronagraph, which is designed for the ground-based telescope especially with a central obstruction and spider structures. The transmission filter is circular symmetrically coated with inconel film on one surface and manufactured with a precisely position-controlled physical mask during the coating procedure. At first, the transmission tolerance of the filter is controlled within 5% for each circular step. The target contrast of the coronagraph is set to be 10-5~10-7 at an inner working angle around 5λ/D. Based on the high-contrast imaging test-bed in the laboratory, the point spread function image of the coronagraph is obtained and it has delivered a contrast better than 10-6 at 5λ/D. As a follow-up effort, the transmission error should be controlled in 2% and the transmission for such filter will be optimized in the near infrared wavelength, which should deliver better performances. Finally, it is shown that the transmission-filter coronagraph is a promising technique to be used for the direct imaging of exoplanets from the ground.
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Jiangpei Dou, Deqing Ren, Yongtian Zhu, Xi Zhang, and Xue Wang "Testing of a transmission-filter coronagraph for ground-based imaging of exoplanets", Proc. SPIE 7735, Ground-based and Airborne Instrumentation for Astronomy III, 77358E (20 July 2010);

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