31 research outputs found
Design and Modeling of the Off-Axis Parabolic Deformable (OPD) Mirror Laboratory
Coronagraph-equipped direct imaging missions need an active wavefront control system to cancel out the optical aberrations that degrade the performance of the coronagraphs. A fast steering mirror is used to control Line-of-Sight (LoS) pointing error caused by the telescope jitter. In addition to controlling other low-order aberrations such as astigmatism and coma, high stroke, high actuator density deformable mirrors (DMs) are also used to control the electric field at the required high spatial frequencies. We are designing a testbed to verify a different deformable architecture, where the powered optic in the optical train are controllable and have lower actuator count compared to the existing DMs with flat nominal surfaces. This simplifies the packaging issue for space missions and reduces both cost and risk of having the entire coronagraph instrument's performance depending on one or two high-actuator count DMs. The testbed would also be capable of testing different low-order wavefront sensing algorithms, which focuses in the near-term on a new adaptive Kalman filtering and gradient decent method to estimate the harmonic LoS errors that affect space telescopes. In long run, we would test different machine learning techniques to estimate low-order aberrations and non-linear algorithms for digging the region of high contrast called the dark holes (DH)
Simulating reflected light coronagraphy of Earth-like exoplanets with a large IR/O/UV space telescope: impact and calibration of smooth exozodiacal dust
Observing Earth-like exoplanets orbiting within the habitable zone of
Sun-like stars and studying their atmospheres in reflected starlight requires
contrasts of in the visible. At such high contrast,
starlight reflected by exozodiacal dust is expected to be a significant source
of contamination. Here, we present high-fidelity simulations of coronagraphic
observations of a synthetic Solar System located at a distance of 10 pc and
observed with a 12 m and an 8 m circumscribed aperture diameter space telescope
operating at 500 nm wavelength. We explore different techniques to subtract the
exozodi and stellar speckles from the simulated images in the face-on, the 30
deg inclined, and the 60 deg inclined case and quantify the remaining
systematic noise as a function of the exozodiacal dust level of the system. We
find that in the face-on case, the exozodi can be subtracted down to the photon
noise limit for exozodi levels up to zodi using a simple toy model
for the exozodiacal disk, whereas in the 60 deg inclined case this only works
up to zodi. We also investigate the impact of larger wavefront errors
and larger system distance, finding that while the former have no significant
impact, the latter has a strong (negative) impact. Ultimately, we derive a
penalty factor as a function of the exozodi level and system inclination that
should be considered in exoplanet yield studies as a realistic estimate for the
excess systematic noise from the exozodi.Comment: 20 pages, 9 figures, accepted for publication in A
Mitigating Worst-Case Exozodiacal Dust Structure in High-contrast Images of Earth-like Exoplanets
Detecting Earth-like exoplanets in direct images of nearby Sun-like systems
brings a unique set of challenges that must be addressed in the early phases of
designing a space-based direct imaging mission. In particular, these systems
may contain exozodiacal dust, which is expected to be the dominant source of
astrophysical noise. Previous work has shown that it may be feasible to
subtract smooth, symmetric dust from observations; however, we do not expect
exozodiacal dust to be perfectly smooth. Exozodiacal dust can be trapped into
mean motion resonances with planetary bodies, producing large-scale structures
that orbit in lock with the planet. This dust can obscure the planet,
complicate noise estimation, or be mistaken for a planetary body. Our ability
to subtract these structures from high-contrast images of Earth-like exoplanets
is not well understood. In this work, we investigate exozodi mitigation for
Earth--Sun-like systems with significant mean motion resonant disk structures.
We find that applying a simple high-pass filter allows us to remove structured
exozodi to the Poisson noise limit for systems with inclinations
and up to 100 zodis. However, subtracting exozodiacal disk structures from
edge-on systems may be challenging, except for cases with densities zodis.
For systems with three times the dust of the Solar System, which is the median
of the best fit to survey data in the habitable zones of nearby Sun-like stars,
this method shows promising results for mitigating exozodiacal dust in future
HWO observations, even if the dust exhibits significant mean-motion resonance
structure.Comment: Accepted to AJ. 18 pages, 10 figure
A Demonstration of Spectral and Spatial Interferometry at THz Frequencies
A laboratory prototype spectral/spatial interferometer has been constructed
to demonstrate the feasibility of the double Fourier technique at Far Infrared
(FIR) wavelengths (0.15 - 1 THz). It is planned to use this demonstrator to
investigate and validate important design features and data processing methods
for future astronomical FIR interferometer instruments. In building this
prototype we have had to address several key technologies to provide an end-end
system demonstration of this double Fourier interferometer. We report on the
first results taken when viewing single slit and double slit sources at the
focus of a large collimator used to simulate real sources at infinity. The
performance of the prototype instrument for these specific field geometries is
analyzed to compare with the observed interferometric fringes and to
demonstrate image reconstruction capabilities.Comment: Accepted for publication in Applied Optic
The Wide-Field Spatio-Spectral Interferometer: System Overview, Data Synthesis and Analysis
The Wide-field Imaging Interferometry Testbed (WIIT) is a double Fourier (DF) interferometer operating at optical wavelengths, and provides data that are highly representative of those from a space-based far-infrared interferometer like SPIRIT. We have used the testbed to observe both geometrically simple and astronomically representative test scenes. Here we present an overview of the astronomical importance of high angular resolution at the far infrared, followed by the description of the optical set-up of WIIT, including the source simulator CHIP (Calibrated Hyperspectral Image Projector). We describe our synthesis algorithms used in the reconstruction of the input test scenes via a simulation of the most recent measurements. The updated algorithms, which include instruments artifacts that allow the synthesis of DF experimental data, are presented and the most recent results analyzed
Recent Experiments Conducted with the Wide-Field Imaging Interferometry Testbed (WIIT)
The Wide-field Imaging Interferometry Testbed (WIIT) was developed at NASA's Goddard Space Flight Center to demonstrate and explore the practical limitations inherent in wide field-of-view double Fourier (spatio-spectral) interferometry. The testbed delivers high-quality interferometric data and is capable of observing spatially and spectrally complex hyperspectral test scenes. Although WIIT operates at visible wavelengths, by design the data are representative of those from a space-based far-infrared observatory. We used WIIT to observe a calibrated, independently characterized test scene of modest spatial and spectral complexity, and an astronomically realistic test scene of much greater spatial and spectral complexity. This paper describes the experimental setup, summarizes the performance of the testbed, and presents representative data
Multimode simulations of a wide Field of View double-fourier far-infrared spatio-spectral interferometer
In the absence of 50 m class space-based observatories, sub-arc-second astronomy spanning the full far-infrared
wavelength range will require space-based long-baseline interferometry. The long baselines of up to 10’s of meteres
are necessary to achieve sub arcsecond resolution demanded by the science goals. Also, practical observing times
command a field of view toward an arc minute or so, not achievable with a single on-axis coherent detector. This
paper is concerned with an application of an end-to-end instrument simulator PyFIInS, developed as part of the
FISICA project under funding from the European Commission’s 7th Framework Programme for Research and
Technological Development (FP7). Predicted results of wide field of view spatio-spectral interferometry through
simulations of a long-baseline, double-Fourier, far-infrared interferometer concept are presented and analysed. It
is shown how such an interferometer, illuminated by a multimode detector can recover a large field of view at
sub-arcsecond angular resolution, resulting in similar image quality as that achieved by illuminating the system
with an array of coherent detectors. Through careful analysis, the importance of accounting for the correct
number of higher-order optical modes is demonstrated, as well as accounting for both orthogonal polarisations.
Given that it is very difficult to manufacture waveguide and feed structures at sub-mm wavelengths, the larger
multimode design is recommended over the array of smaller single mode detectors. A brief note is provided in
the conclusion of this paper, addressing a novel, more elegant solution to modelling far-infrared interferometers,
which holds promise for improving the computational efficiency of the simulations presented here
A Dispersive Backend Design for the 'Double-Fourier' Interferometer BETTII
BETTII (Balloon Experimental Twin Telescope for Infra-red Interferometry) is designed to provide high angular resolution spectroscopic data in the far-infrared (FIR) wavelengths. The most significant limitation for BETTII is its sensitivity; obtaining spectral signal-to-noise ratio greater than 5 in less than 10 minutes requires sources greater than 13 Janskys (Jy). One possible way to improve the signal-to-noise ratio (SNR) for future BETTII flights is by reducing the spectral bandwidth post beam-combination. This involves using a dispersive element to spread out a polychromatic point source PSF (Point Spread Function) on the detector array, such that each pixel corresponds to a small fraction of the bandwidth. This results in a broader envelope of the interferometric fringe pattern allowing more fringes to be detected, and thereby improving the spectral SNR. Here we present the analysis and optical design of the dispersive backend, discussing the tradeoffs and how it can be combined with the existing design