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Title: High-contrast imaging with an arbitrary aperture: Active compensation of aperture discontinuities

Abstract

We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential deformable mirrors (DMs) to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of DM surfaces that yield high-contrast point-spread functions is not linear, and nonlinear methods are needed to find the true minimum in the optimization topology. We solve the highly nonlinear Monge-Ampere equation that is the fundamental equation describing the physics of phase-induced amplitude modulation. We determine the optimum configuration for our two sequential DM system and show that high-throughput and high-contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to the James Webb Space Telescope, ACAD can attain at least 10{sup –7} in contrast and an order of magnitude higher for both the future extremely large telescopes and on-axis architectures reminiscent of the Hubble Space Telescope. We show that the converging nonlinear mappings resulting from our DM shapes actually damp near-field diffraction artifacts in the vicinity of the discontinuities.more » Thus, ACAD actually lowers the chromatic ringing due to diffraction by segment gaps and struts while not amplifying the diffraction at the aperture edges beyond the Fresnel regime. This outer Fresnel ringing can be mitigated by properly designing the optical system. Consequently, ACAD is a true broadband solution to the problem of high-contrast imaging with segmented and/or on-axis apertures. We finally show that once the nonlinear solution is found, fine tuning with linear methods used in wavefront control can be applied to further contrast by another order of magnitude. Generally speaking, the ACAD technique can be used to significantly improve a broad class of telescope designs for a variety of problems.« less

Authors:
;  [1]
  1. Department of Physics and Astronomy, Johns Hopkins University, Baltimore, MD (United States)
Publication Date:
OSTI Identifier:
22342078
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal
Additional Journal Information:
Journal Volume: 769; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0004-637X
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; AMPLITUDES; APERTURES; CONFIGURATION; DEFORMATION; DETECTION; DIFFRACTION; EQUATIONS; EXCURSIONS; IMAGES; MATHEMATICAL SOLUTIONS; MODULATION; OPTICAL SYSTEMS; RESOLUTION; SATELLITES; SPACE; SURFACES; TELESCOPES

Citation Formats

Pueyo, Laurent, and Norman, Colin. High-contrast imaging with an arbitrary aperture: Active compensation of aperture discontinuities. United States: N. p., 2013. Web. doi:10.1088/0004-637X/769/2/102.
Pueyo, Laurent, & Norman, Colin. High-contrast imaging with an arbitrary aperture: Active compensation of aperture discontinuities. United States. https://doi.org/10.1088/0004-637X/769/2/102
Pueyo, Laurent, and Norman, Colin. 2013. "High-contrast imaging with an arbitrary aperture: Active compensation of aperture discontinuities". United States. https://doi.org/10.1088/0004-637X/769/2/102.
@article{osti_22342078,
title = {High-contrast imaging with an arbitrary aperture: Active compensation of aperture discontinuities},
author = {Pueyo, Laurent and Norman, Colin},
abstractNote = {We present a new method to achieve high-contrast images using segmented and/or on-axis telescopes. Our approach relies on using two sequential deformable mirrors (DMs) to compensate for the large amplitude excursions in the telescope aperture due to secondary support structures and/or segment gaps. In this configuration the parameter landscape of DM surfaces that yield high-contrast point-spread functions is not linear, and nonlinear methods are needed to find the true minimum in the optimization topology. We solve the highly nonlinear Monge-Ampere equation that is the fundamental equation describing the physics of phase-induced amplitude modulation. We determine the optimum configuration for our two sequential DM system and show that high-throughput and high-contrast solutions can be achieved using realistic surface deformations that are accessible using existing technologies. We name this process Active Compensation of Aperture Discontinuities (ACAD). We show that for geometries similar to the James Webb Space Telescope, ACAD can attain at least 10{sup –7} in contrast and an order of magnitude higher for both the future extremely large telescopes and on-axis architectures reminiscent of the Hubble Space Telescope. We show that the converging nonlinear mappings resulting from our DM shapes actually damp near-field diffraction artifacts in the vicinity of the discontinuities. Thus, ACAD actually lowers the chromatic ringing due to diffraction by segment gaps and struts while not amplifying the diffraction at the aperture edges beyond the Fresnel regime. This outer Fresnel ringing can be mitigated by properly designing the optical system. Consequently, ACAD is a true broadband solution to the problem of high-contrast imaging with segmented and/or on-axis apertures. We finally show that once the nonlinear solution is found, fine tuning with linear methods used in wavefront control can be applied to further contrast by another order of magnitude. Generally speaking, the ACAD technique can be used to significantly improve a broad class of telescope designs for a variety of problems.},
doi = {10.1088/0004-637X/769/2/102},
url = {https://www.osti.gov/biblio/22342078}, journal = {Astrophysical Journal},
issn = {0004-637X},
number = 2,
volume = 769,
place = {United States},
year = {Sat Jun 01 00:00:00 EDT 2013},
month = {Sat Jun 01 00:00:00 EDT 2013}
}