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Proximity Glare Suppression for Astronomical Direct Detection of Exoplanets

Description:

Control of Scattered Starlight with Coronagraphs and Starshades


This subtopic addresses the unique problem of imaging and spectroscopic characterization of faint astrophysical objects that are located within the obscuring glare of much brighter stellar sources. Examples include planetary systems beyond our own, the detailed inner structure of galaxies with very bright nuclei, binary star formation, and stellar evolution. Contrast ratios of one million to ten billion over an angular spatial scale of 0.05-1.5 arcsec are typical of these objects. Achieving a very low background requires control of both scattered and diffracted light. The failure to control either amplitude or phase fluctuations in the optical train severely reduces the effectiveness of starlight cancellation schemes.

This innovative research focuses on advances in coronagraphic instruments, starlight cancellation instruments, and potential occulting technologies that operate at visible and near infrared wavelengths. The ultimate application of these instruments is to operate in space as part of a future observatory mission concepts such as the Habitable Exoplanet Observatory (HabEx) and the Large UV Optical Infrared Surveyor (LUVOIR). Measurement techniques include imaging, photometry, spectroscopy, and polarimetry. There is interest in component development and innovative instrument design, as well as in the fabrication of subsystem devices to include, but not limited to, the following areas:

Starlight Suppression Technologies:

 

  • Hybrid metal/dielectric, and polarization apodization masks for diffraction control of phase and amplitude for coronagraph scaled starshade experiments.
  • Low-scatter, low-reflectivity, sharp, flexible edges for control of solar scatter in starshades.
  • Systems to measure spatial optical density, phase inhomogeneity, scattering, spectral dispersion, thermal variations, and to otherwise estimate the accuracy of high-dynamic range apodizing masks.
  • Methods to distinguish the coherent and incoherent scatter in a broad band speckle field.


Wavefront Measurement and Control Technologies:

 

  • Small stroke, high precision, deformable mirrors and associated driving electronics scalable to 10,000 or more actuators (both to further the state-of-the-art towards flight-like hardware and to explore novel concepts). Multiple deformable mirror technologies in various phases of development and processes are encouraged to ultimately improve the state-of-the-art in deformable mirror technology. Process improvements are needed to improve repeatability, yield, and performance precision of current devices.
  • Multiplexers with ultra-low power dissipation for electrical connection to deformable mirrors.
  • Low-order wavefront sensors for measuring wavefront instabilities to enable real-time control and post-processing of aberrations.
  • Thermally and mechanically insensitive optical benches and systems.


Optical Coating and Measurement Technologies:

 

  • Instruments capable of measuring polarization cross-talk and birefringence to parts per million.
  • Polarization-insensitive coatings for large optics.
  • Methods to measure the spectral reflectivity and polarization uniformity across large optics.
  • Methods to apply carbon nanotube coatings on the surfaces of the coronagraphs for broadband suppression from visible to NIR.


Other:

 

  • Artificial star and planet point sources, with 1e10 dynamic range and uniform illumination of an f/25 optical system, working in the visible and near infrared.

 

These technologies are directly applicable to the Wide Field Infrared Survey Telescope (WFIRST) CGI, the HabEx, and LUVOIR concept studies.

 

The expected TRL for this project is 3 to 5.

 

References:

 

  • See the International Society for Optics and Photonics (SPIE) conference papers and articles published in Journal of Astronomical Telescopes and Instrumentation on high contrast coronagraphy, segmented coronagraph design and analysis, and starshades.
  • https://wfirst.gsfc.nasa.gov/
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