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11 September 2015 Demonstrating broadband billion-to-one contrast with the Visible Nulling Coronagraph
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The key to broadband operation of the Visible Nulling Coronagraph (VNC) is achieving a condition of quasi-achromatic destructive interference between combined beams. Here we present efforts towards meeting this goal using Fresnel rhombs in each interferometric arm as orthogonally aligned half wave phase retarders. The milestone goal of the demonstration is to achieve 1 × 10−9 contrast at 2λ/D over a 40 nm bandpass centered at 633 nm. Rhombs have been designed and fabricated, and a multi-step approach to alignment using coarse positioners for each rhomb and pair has been developed to get within range of piezo stages used for fine positioning. The previously demonstrated narrowband VNC sensing and control approach that uses a segmented deformable mirror is being adapted to broadband to include fine positioning of the piezo-mounted rhombs, all demonstrated in a low-pressure environment.
© (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Brian A. Hicks, Richard G. Lyon, Peter Petrone III, Ian J. Miller, Matthew R. Bolcar, Mark Clampin, Michael A. Helmbrecht, and Udayan Mallik "Demonstrating broadband billion-to-one contrast with the Visible Nulling Coronagraph", Proc. SPIE 9605, Techniques and Instrumentation for Detection of Exoplanets VII, 96050K (11 September 2015);


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