112 research outputs found
Simulating the efficacy of the implicit-electric-field-conjugation algorithm for the Roman Coronagraph with noise
The Roman Coronagraph is expected to perform its high-order wavefront sensing
and control (HOWFSC) with a ground-in-the-loop scheme due to the computational
complexity of the Electric-Field-Conjugation (EFC) algorithm. This scheme
provides the flexibility to alter the HOWFSC algorithm for given science
objectives. A new alternative implicit-EFC algorithm is of particular interest
as it requires no optical model to create a dark-hole, making the final
contrast independent of the model accuracy. The intended HOWFSC scheme involves
running EFC while observing a bright star such as Puppis to create the
initial dark-hole, then slew to the science target while maintaining the
contrast with low-order WFSC over the given observation.
Given a similar scheme, the efficacy of iEFC is simulated for two coronagraph
modes, namely the Hybrid Lyot Coronagraph (HLC) and the wide-field-of-view
Shaped-Pupil-Coronagraph (SPC-WFOV). End-to-end physical optics models for each
mode serve as the tool for the simulations. Initial monochromatic simulations
are presented and compared with monochromatic EFC results obtained with the
FALCO software. Various sets of calibration modes are tested to understand the
optimal modes to use when generating an iEFC response matrix. Further iEFC
simulations are performed using broadband images with the assumption that
Puppis is the stellar object being observed. Shot noise, read noise,
and dark current are included in the broadband simulations to determine if iEFC
could be a suitable alternative to EFC for the Roman Coronagraph.Comment: 15 pages, 16 figure
Microfabricated pinholes for high contrast imaging testbeds
In order to reach contrast ratios of and beyond, coronagraph
testbeds need source optics that reliably emulate nearly-point-like starlight,
with microfabricated pinholes being a compelling solution. To verify, a
physical optics model of the Space Coronagraph Optical Bench (SCoOB) source
optics, including a finite-difference time-domain (FDTD) pinhole simulation,
was created. The results of the FDTD simulation show waveguide-like behavior of
pinholes. We designed and fabricated microfabricated pinholes for SCoOB made
from an aluminum overcoated silicon nitride film overhanging a silicon wafer
substrate, and report characterization of the completed pinholes.Comment: Submitted to SPIE Optical Engineering + Applications (OP23O
Focus diverse phase retrieval testbed development of continuous wavefront sensing for space telescope applications
Continuous wavefront sensing on future space telescopes allows relaxation of
stability requirements while still allowing on-orbit diffraction-limited
optical performance. We consider the suitability of phase retrieval to
continuously reconstruct the phase of a wavefront from on-orbit irradiance
measurements or point spread function (PSF) images. As phase retrieval
algorithms do not require reference optics or complicated calibrations, it is a
preferable technique for space observatories, such as the Hubble Space
Telescope or the James Webb Space Telescope. To increase the robustness and
dynamic range of the phase retrieval algorithm, multiple PSF images with known
amount of defocus can be utilized. In this study, we describe a recently
constructed testbed including a 97 actuator deformable mirror, changeable
entrance pupil stops, and a light source. The aligned system wavefront error is
below ~30nm. We applied various methods to generate a known wavefront error,
such as defocus and/or other aberrations, and found the accuracy and precision
of the root mean squared error of the reconstructed wavefronts to be less than
~10nm and ~2nm, respectively. Further, we discuss the signal-to-noise ratios
required for continuous dynamic wavefront sensing. We also simulate the case of
spacecraft drifting and verify the performance of the phase retrieval algorithm
for continuous wavefront sensing in the presence of realistic disturbances
Exploring the reactivity of donor-stabilised phosphenium cations: Lewis acid catalysed reduction of chlorophosphanes by silanes
Phosphane-stabilised phosphenium cations react with silanes to effect either reduction to primary or secondary phosphanes, or formation of P-P bonded species depending upon counter-anion. This operates for in situ generated phosphenium cations, allowing catalytic reduction of P(III)-Cl bonds in the absence of strong reducing agents. Anion and substituent dependence studies have allowed insight into the competing mechanisms involved
Laboratory demonstration of the triple-grating vector vortex coronagraph
The future Habitable Worlds Observatory aims to characterize the atmospheres
of rocky exoplanets around solar-type stars. The vector vortex coronagraph
(VVC) is a main candidate to reach the required contrast of .
However, the VVC requires polarization filtering and every observing band
requires a different VVC. The triple-grating vector vortex coronagraph (tgVVC)
aims to mitigate these limitations by combining multiple gratings that minimize
the polarization leakage over a large spectral bandwidth. In this paper, we
present laboratory results of a tgVVC prototype using the In-Air Coronagraphic
Testbed (IACT) facility at NASA's Jet Propulsion Laboratory and the Space
Coronagraph Optical Bench (SCoOB) at the University of Arizona Space
Astrophysics Lab (UASAL). We study the coronagraphic performance with
polarization filtering at 633 nm and reach a similar average contrast of between 3-18 at the IACT, and
between 3-14 at SCoOB. We explore the limitations of the tgVVC by
comparing the testbed results. We report on other manufacturing errors and ways
to mitigate their impact.Comment: 9 pages, 5 figures, SPIE Optics + Photonics - Techniques and
Instrumentation for Detection of Exoplanets X
Land use change alters carbon composition and degree of decomposition of tropical peat soils
Drainage associated with land use change in tropical peatlands has increased the rate of decomposition of peat soils and contributed to CO2 emissions. Increased decomposition may result in changes in the composition of the soil organic carbon (SOC). We examined the carbon functional group composition and degree of decomposition of peat soils under five different land uses to understand the effects of changing management intensity on tropical peatland soils. Samples were collected from seven sites spanning five different land uses (forest, shrubland, fernland, revegetation, smallholder oil palm) at the Pedamaran peatland in South Sumatra, Indonesia. SOC composition, measured by Solid-state 13C Nuclear Magnetic Resonance (NMR) spectroscopy, was dominated by the alkyl carbon (C) functional group in managed peatlands. However, in the forest far from drainage canals, the SOC comprised predominantly O-alkyl C. The contributions of the functional groups ketone C, carbonyl C and O-aryl C were low and tended to occur in stable proportions throughout the soil profiles. Drainage and land use change significantly affected peat carbon chemistry. The effects were greatest under oil palm, where O-alkyl C had been depleted rapidly under aerobic conditions leading to a change in the dominant carbon functional group from O-alkyl C to alkyl C. Furthermore, our results indicate that the alkyl C:O-alkyl C ratio is a more useful and informative indicator of the degree of decomposition of peat soil than the traditionally used C:N ratio. This more nuanced understanding of the different types of carbon that make up tropical peat soils under different land uses can be applied to support peatland restoration. In particular, nutrient cycling and water availability are likely to be influenced by carbon functional group and degree of decomposition. In order to reduce fire risk and support Indonesia’s aspirations to manage the national forest estate as a net carbon sink, further research into the links between peat soil organic carbon chemistry, revegetation performance and new peat accumulation is recommended
Estimation of polarization aberrations and their effect on the coronagraphic performance for future space telescopes
A major goal of proposed future space observatories, such as the Habitable
World Observatory, is to directly image and characterize Earth-like planets
around Sun-like stars to search for habitability signatures requiring the
starlight suppression (contrast) of 1e-10. One of the significant aspects
affecting this contrast is the polarization aberrations generated from the
reflection from mirror surfaces. The polarization aberrations are the
phase-dependent amplitude and phase patterns originating from the Fresnel
reflections of the mirror surfaces. These aberrations depend on the angle of
incidence and coating parameters of the surface. This paper simulates the
polarization aberrations for an on-axis and off-axis TMA telescope of a 6.5 m
monolithic primary mirror. We analyze the polarization aberrations and their
effect on the coronagraphic performance for eight different recipes of mirror
coatings for Astronomical filter bands g-I: three single-layer metal coatings
and five recipes of protective coatings. First, the Jones pupils are estimated
for each coating and filter band using the polarization ray tracing in Zemax.
Then, we propagate these Jones pupils through a Vector Vortex Coronagraph and
Perfect Coronagraphs using hcipy, a physical optics-based simulation framework.
The analysis shows that the two main polarization aberrations generated from
the four mirrors are the retardance-defocus and retardance-tilt. The
simulations also show that the coating plays a significant role in determining
the strength of the aberrations. The bare/oxi-aluminum and Al+18nm LiF coating
outperforms all the other coatings by one order of magnitude.Comment: 13 pages, 11 figures, SPIE Optics+Photonics 2023 proceeding, Paper
no: 12680-2
The space coronagraph optical bench (SCoOB): 2. wavefront sensing and control in a vacuum-compatible coronagraph testbed for spaceborne high-contrast imaging technology
The 2020 Decadal Survey on Astronomy and Astrophysics endorsed space-based
high contrast imaging for the detection and characterization of habitable
exoplanets as a key priority for the upcoming decade. To advance the maturity
of starlight suppression techniques in a space-like environment, we are
developing the Space Coronagraph Optical Bench (SCoOB) at the University of
Arizona, a new thermal vacuum (TVAC) testbed based on the Coronagraphic Debris
Exoplanet Exploring Payload (CDEEP), a SmallSat mission concept for high
contrast imaging of circumstellar disks in scattered light. When completed, the
testbed will combine a vector vortex coronagraph (VVC) with a Kilo-C
microelectromechanical systems (MEMS) deformable mirror from Boston
Micromachines Corp (BMC) and a self-coherent camera (SCC) with a goal of raw
contrast surpassing at visible wavelengths. In this proceedings, we
report on our wavefront sensing and control efforts on this testbed in air,
including the as-built performance of the optical system and the implementation
of algorithms for focal-plane wavefront control and digging dark holes (regions
of high contrast in the focal plane) using electric field conjugation (EFC) and
related algorithms.Comment: 7 pages, 5 figures, SPIE Astronomical Telescopes and Instrumentation
202
Polarization aberrations in next-generation giant segmented mirror telescopes (GSMTs) I. Effect on the coronagraphic performance
Next-generation large segmented mirror telescopes are expected to perform
direct imaging and characterization of Earth-like rocky planets, which requires
contrast limits of to at wavelengths from I to J band. One
critical aspect affecting the raw on-sky contrast are polarization aberrations
arising from the reflection from the telescope's mirror surfaces and instrument
optics. We simulate the polarization aberrations and estimate their effect on
the achievable contrast for three next-generation ground-based large segmented
mirror telescopes. We performed ray-tracing in Zemax and computed the
polarization aberrations and Jones pupil maps using the polarization
ray-tracing algorithm. The impact of these aberrations on the contrast is
estimated by propagating the Jones pupil maps through a set of idealized
coronagraphs using hcipy, a physical optics-based simulation framework. The
optical modeling of the giant segmented mirror telescopes (GSMTs) shows that
polarization aberrations create significant leakage through a coronagraphic
system. The dominant aberration is retardance defocus, which originates from
the steep angles on the primary and secondary mirrors. The retardance defocus
limits the contrast to to at 1 at visible
wavelengths, and to at infrared wavelengths. The
simulations also show that the coating plays a major role in determining the
strength of the aberrations. Polarization aberrations will need to be
considered during the design of high-contrast imaging instruments for the next
generation of extremely large telescopes. This can be achieved either through
compensation optics, robust coronagraphs, specialized coatings, calibration,
and data analysis approaches or by incorporating polarimetry with high-contrast
imaging to measure these effects.Comment: 18 pages, 12 figures, Accepted in Astronomy & Astrophysics manuscript
no. aa45651-2
The Space Coronagraph Optical Bench (SCoOB): 1. Design and Assembly of a Vacuum-compatible Coronagraph Testbed for Spaceborne High-Contrast Imaging Technology
The development of spaceborne coronagraphic technology is of paramount
importance to the detection of habitable exoplanets in visible light. In space,
coronagraphs are able to bypass the limitations imposed by the atmosphere to
reach deeper contrasts and detect faint companions close to their host star. To
effectively test this technology in a flight-like environment, a high-contrast
imaging testbed must be designed for operation in a thermal vacuum (TVAC)
chamber. A TVAC-compatible high-contrast imaging testbed is undergoing
development at the University of Arizona inspired by a previous mission
concept: The Coronagraphic Debris and Exoplanet Exploring Payload (CDEEP). The
testbed currently operates at visible wavelengths and features a Boston
Micromachines Kilo-C DM for wavefront control. Both a vector vortex coronagraph
and a knife-edge Lyot coronagraph operating mode are under test. The optics
will be mounted to a 1 x 2 meter pneumatically isolated optical bench designed
to operate at 10^-8 torr and achieve raw contrasts of 10^-8 or better. The
validation of our optical surface quality, alignment procedure, and first light
results are presented. We also report on the status of the testbed's
integration in the vaccum chamber.Comment: 14 pages, 9 figure
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