Terrestrial exoplanet coronagraph image quality polarization aberrations in Habex

J. B. Breckinridge, M. Kupinski, J. Davis, B. Daugherty, R. A. Chipman

Research output: Chapter in Book/Report/Conference proceedingConference contribution

8 Scopus citations


Direct imaging and spectroscopy of terrestrial exoplanets requires the control of vector electromagnetic fields to approximately one part in ten to the fifth over a few milliarc second FOV to achieve the necessary 10-10 intensity contrast levels. Observations using space telescopes are necessary to achieve these levels of diffracted and scattered light control. The highly reflecting metal mirrors and their coatings needed to image these very faint exoplanets introduce polarization into the wavefront, which, in turn affects image quality and reduces exoplanet yield unless corrected. To identify and create the technologies and the electro-optical/mechanical-spacecraft systems models that will achieve these levels, NASA is currently developing two mission concepts, each with their own hardware vision. These are: The Habex, a habitable planet explorer and the LUVOIR, a Large Ultra-Violet Optical-Infrared space telescope system. This paper reports the results of polarization ray-tracing the HabEx detailed optical prescription provided by the project to the authors in the fall of 2017. Diattenuation and retardance across both the exit pupil associated with the occulting mask and the exit pupil associated with the coronagraph image plane are given as well as the corresponding Jones pupil matrices. These are calculated assuming isotropic coatings on all mirrors. Analysis and physical measurements indicates that the specification of the primary mirror for exoplanet coronagraphs will need to include a constraint on spatially varying polarization reflectivity (anisotropic coatings). The Jones exit-pupil phase terms, phi XX and phi YY just before the occulting mask differ in shape and are displaced one from the other by about 10 milli-waves. This shows that A/O, which corrects for geometric path differences, cannot completely correct for wavefront errors introduced by polarization for this particular prescription for HabEx. We suggest that these differences may be corrected by adjusting the opto-mechanical design to change angles of incidence on mirrors and corrected by adjusting the design of the dielectric coatings on the highly-reflecting mirror surfaces. Super-posing the phase of XX onto the phase of YY and then correcting using A/O will assure maximum power transmittance through the system and best contrast. These aspects require further investigation.

Original languageEnglish (US)
Title of host publicationSpace Telescopes and Instrumentation 2018
Subtitle of host publicationOptical, Infrared, and Millimeter Wave
EditorsGiovanni G. Fazio, Howard A. MacEwen, Makenzie Lystrup
ISBN (Print)9781510619494
StatePublished - 2018
EventSpace Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave - Austin, United States
Duration: Jun 10 2018Jun 15 2018

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X
ISSN (Electronic)1996-756X


OtherSpace Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave
Country/TerritoryUnited States


  • Coatings
  • Coronagraph
  • Exoplanet
  • HabEx
  • Physical optics
  • Polarization aberration
  • Telescopes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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