The role of narrow-angle forward surface scatter and particulate scatter in exoplanet exploration

Pfisterer, Richard N.; Harvey, James E.; Breckinridge, James B.

doi:10.1117/12.2314229

Cited by 3 publications

(2 citation statements)

References 3 publications

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“…angle at which scatter becomes a constant incoherent background). Per Pfisterer [11], "an accurate measurement of L is difficult due to experimental instrument signature and diffraction issues, theorists have proposed that reasonable values for L lie in the range of 0.0001 to 0.01 radians (20.6 to 2063 arc-seconds) from specular." Thus, GHS theory implies that near angle scatter across the entire dark hole is Lambertian, i.e.…”

Section: Generalized Harvey-shack (Ghs) Surface Scatter Theorymentioning

confidence: 99%

Assessment of near-angle scatter on exo-Earth coronagraphy

Stahl

2023

UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts XI

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A first order single surface analysis indicates that, to enable coronagraphic detection and characterization of exo-Earth planets, near angle scatter must be considered when specifying optical surfaces for a potential Habitable World Observatory. Based on arbitrary error budget allocations and using Rayleigh-Rice Vector Scatter Theory, Generalized Harvey-Shack Scalar Scatter Theory, and Greynolds Approximation, 'placeholder' specifications for the primary mirror are derived: Static Surface Roughness < 1 nm rms, and Dynamic Surface Roughness < 1 pm PV. These specifications will change once error budget allocations are defined. Analysis does not include scatter from more than just the primary mirror, coating structure, edges, contamination, micrometeoroid impacts, etc.

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Section: Generalized Harvey-shack (Ghs) Surface Scatter Theorymentioning

confidence: 99%

Assessment of near-angle scatter on exo-Earth coronagraphy

Stahl

2023

UV/Optical/IR Space Telescopes and Instruments: Innovative Technologies and Concepts XI

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“…al. 6 The pupil is covered with 3 diffraction gratings, each clocked 60 degrees relative to the other Figure 3 shows the pupil, left and the irradiance at the image plane for an on-axis star at 1-micron wavelength for the 30-meter diameter CELT (now called the Thirty Meter Telescope, TMT) 7 . The PSF is plotted on a log10 intensity scale and the grey scale across the top of the PSF image on the right shows intensity order of magnitude from 10 0 to 10 -10 .…”

Section: Ground and Space Telescopesmentioning

confidence: 99%

Exoplanet telescope diffracted light minimized: the pinwheel-pupil solution

Breckinridge

Harvey²,

Crabtree

et al. 2018

Space Telescopes and Instrumentation 2018: Optical, Infrared, and Millimeter Wave

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Terrestrial exoplanets shine in light reflected from a parent star. Optical spectra are required to provide evidence of a life-supporting environment. Exoplanets are very faint and their optical spectra are contaminated by the spectrum of the parent star. High angular resolution provided by large apertures is needed to distinguish between the spectrum of the exoplanet and its star. Today, large aperture telescopes use segmented primary mirrors that employ close-packed hexagonal segments. The telescope primary mirror is periodically discontinuous with straight lines. These discontinuities scatter unwanted radiation from the much brighter parent star across the field of view to obscure the light from the very faint terrestrial exoplanet. These discontinuities, which mimic a diffraction grating, result in a non-uniform distribution of background light across the image plane. This non-uniformity masks or hides exoplanets from view, to reduce the number of exoplanets that can be observed with a large aperture telescope or to reduce the quality of spectra and thus lead to misinterpretation of data. Here we introduce the concept of the pinwheel pupil whose unique diffraction pattern significantly reduces the non-uniform distribution of background radiation. Diffraction patterns from pinwheel pupils are compared to the monolithic filled aperture, the classical Cassegrain, the 60-degree symmetry of the hexagonal segments (JWST, E-ELT, etc.). Diffraction "spikes" are reduced by at least 10 5. We discuss the "pinwheel pupil" advantages to spectroscopy, image processing, and observatory operations. We show that, segment fabrication of curved-sided mirrors is not more difficult than fabrication of hexagonal mirror segments.. This is the report of quantitative study of Fraunhofer (far field) diffraction patterns produced by three different topologies or architectures of mirror segmentation, when illuminated by a plane wave of monochromatic white-light. A plot, in angular units of the intensity as a function of azimuth, Phi f , within annular rings at different FOVs, centered on the system axis of the diffraction pattern will be presented. The advantages of the segmented pinwheel pupil is discussed.

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Retrieved Atmospheres and Inferred Surface Properties for Terrestrial Exoplanets Using Transmission and Reflected-light Spectroscopy

Gilbert-Janizek,

Meadows,

Lustig-Yaeger

2024

Planet. Sci. J.

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Future astrophysics missions will seek extraterrestrial life via transmission and direct-imaging observations. To assess habitability and biosignatures, we need robust retrieval tools to analyze observed spectra, and infer surface and atmospheric properties with their uncertainties. We use a novel retrieval tool to assess accuracy in characterizing near-surface habitability and biosignatures via simulated transmission and direct-imaging spectra, based on the Origins Space Telescope (Origins) and LUVOIR mission concepts. We assess our ability to discriminate between an Earth-like and a false-positive O3 TRAPPIST-1 e with transmission spectroscopy. In reflected light, we assess the robustness of retrieval results to unmodeled cloud extinction. We find that assessing habitability using transmission spectra may be challenging due to relative insensitivity to surface temperature and near-surface H2O abundances. Nonetheless, our order-of-magnitude H2O constraints can discriminate extremely desiccated worlds. Direct imaging is insensitive to surface temperature and subject to the radius/albedo degeneracy, but this method proves highly sensitive to surface water abundance, achieving retrieval precision within 0.1% even with partial clouds. Concerning biosignatures, Origins-like transmission observations (t = 40 hr) may detect the CO2/CH4 pair on M-dwarf planets and differentiate between biological and false-positive O3 using H2O and abundant CO. In contrast, direct-imaging observations with LUVOIR-A (t = 10 hr) are better suited to constraining O2 and O3, and may be sensitive to wavelength-dependent water cloud features, but will struggle to detect modern-Earth-like abundances of methane. For direct imaging, we weakly detect a stratospheric ozone bulge by fitting the near-UV wings of the Hartley band.

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The role of narrow-angle forward surface scatter and particulate scatter in exoplanet exploration

Cited by 3 publications

References 3 publications

Assessment of near-angle scatter on exo-Earth coronagraphy

Assessment of near-angle scatter on exo-Earth coronagraphy

Exoplanet telescope diffracted light minimized: the pinwheel-pupil solution

Retrieved Atmospheres and Inferred Surface Properties for Terrestrial Exoplanets Using Transmission and Reflected-light Spectroscopy

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