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 $\zeta$ 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 $\zeta$ 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 $10^{-8}$ 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 $10^{-10}$. 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 $2 \times 10^{-8}$ between 3-18 $\lambda/D$ at the IACT, and $6 \times 10^{-8}$ between 3-14 $\lambda/D$ 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 $10^{-8}$ 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 $10^{-7}$ to $10^{-8}$ 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 $10^{-5}$ to $10^{-4}$ at 1 $\lambda/D$ at visible wavelengths, and $10^{-5}$ to $10^{-6}$ 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