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Proceedings Paper

The COSMO coronagraph optical design and stray light analysis
Author(s): Dennis Gallagher; Zhen Wu; Brandon Larson; Peter G. Nelson; Phil Oakley; Scott Sewell; Steven Tomczyk
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Paper Abstract

The Coronal Solar Magnetism Observatory Large Coronagraph (COSMO-LC) is a 1.5 meter Lyot coronagraph dedicated to measuring magnetic fields and plasma properties in the solar corona. The COSMO-LC will be able to observe coronal emissions lines from 530-1100 nm using a filtergraph instrument. COSMO-LC will have a 1 degree field of view to observe the full solar corona out to 1 solar radius beyond the limb of the sun. This presented challenges due to the large Etendue of the system. The COSMO-LC spatial resolution is 2 arc-seconds per pixel (4k X 4k). The most critical part of the coronagraph is the objective lens that is exposed to direct sunlight that is five orders of magnitude brighter than the corona. Therefore, it is key to the operation of a coronagraph that the objective lens (O1) scatter as little light as possible, on order a few parts per million. The selection of the material and the polish applied to the O1 are critical in reducing scattered light. In this paper we discuss the design of the COSMO-LC and the detailed design of the O1 and other key parts of the COSMO-LC that keep stray light to a minimum. The result is an instrument with stray light below 5 millionths the brightness of the sun 50 arc-seconds from the sun. The COSMO-LC has just had a Preliminary Design Review (PDR) and the PDR design is presented.

Paper Details

Date Published: 27 July 2016
PDF: 17 pages
Proc. SPIE 9906, Ground-based and Airborne Telescopes VI, 990654 (27 July 2016); doi: 10.1117/12.2235234
Show Author Affiliations
Dennis Gallagher, National Ctr. for Atmospheric Research (United States)
Zhen Wu, Nanjing Institute of Astronomical Optics & Technology (China)
Brandon Larson, National Ctr. for Atmospheric Research (United States)
Peter G. Nelson, Sierra Scientific Solutions, LLC (United States)
Phil Oakley, National Ctr. for Atmospheric Research (United States)
Scott Sewell, National Ctr. for Atmospheric Research (United States)
Steven Tomczyk, National Ctr. for Atmospheric Research (United States)

Published in SPIE Proceedings Vol. 9906:
Ground-based and Airborne Telescopes VI
Helen J. Hall; Roberto Gilmozzi; Heather K. Marshall, Editor(s)

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