The Gemini Planet Imager (GPI) is a high-contrast imaging instrument designed to directly detect and characterize young, Jupiter-mass exoplanets. After six years of operation at Gemini South in Chile, the instrument is being upgraded and relocated to Gemini North in Hawaii as GPI 2.0. GPI helped establish that Jovian-mass planets have a higher occurrence rate at smaller separations, motivating several sub-system upgrades to obtain deeper contrasts (up to 20 times improvement to the current limit), particularly at small inner working angles. This enables access to additional science areas for GPI 2.0, including low-mass stars, young nearby stars, solar system objects, planet formation in disks, and planet variability. The necessary instrumental changes required toenable these new scientific goals are to (i) the adaptive optics system, by replacing the current Shack-Hartmann Wavefront Sensor (WFS) with a pyramid WFS and a custom EMCCD, (ii) the integral field spectrograph, by employing a new set of prisms to enable an additional broadband (Y-K band) low spectral resolution mode, as well as replacing the pupil viewer camera with a faster, lower noise C-RED2 camera (iii) the calibration interferometer, by upgrading the low-order WFS used for internal alignment and on-sky target tracking with a C-RED2 camera and replacing the calibration high-order WFS used for measuring and correcting non-common path aberrations with a self coherent camera, (iv) the apodized-pupil Lyot coronagraph designs and (v) the software, to enable high-efficiency queue operations at Gemini North. GPI 2.0 is expected to go on-sky in early 2024. Here I will present the new scientific goals, the key upgrades, the current status and the latest timeline for operations.

GPI2.0 is an upgrade of the high-contrast instrument known as the Gemini Planet Imager (GPI). This new version is scheduled for installation on Gemini North telescope by the end of 2024. In this document, we outline our approach for addressing Non-Common Path Aberrations (NCPA) measurement and correction within the instrument. Our strategy differs significantly from the methods employed in the original GPI. Our proposal involves the utilization of a dedicated Wavefront Sensor (WFS) positioned within the coronagraph branch to accurately measure NCPAs. Subsequently, we will compensate for these aberrations by transmitting offset signals to the adaptive optics WFS. The chosen dedicated WFS will be a Zernike WFS (ZWFS), known for its exceptional sensitivity. This paper provides insights into the integration plan for incorporating the ZWFS into GPI2.0, details its key characteristics, and outlines the methodology for performing phase inversion based on the ZWFS measurements. Additionally, we present the initial results of experimental tests conducted on the SEAL testbed at the University of California, Santa Cruz (UCSC).

The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is a 2 μm to 5 μm, high-contrast Integral Field Spectrograph (IFS) currently being built for Keck Observatory. With both low (R ≲ 250) and medium (R approximately 3500 to 7000) spectral resolution IFS modes, SCALES will detect and characterize significantly colder exoplanets than those accessible with near-infrared (approximately 1 μm to 2 μm) high-contrast spectrographs. This will lead to new progress in exoplanet atmospheric studies, including detailed characterization of benchmark systems that will advance the state of the art of atmospheric modeling. SCALES’ unique modes, while designed specifically for direct exoplanet characterization, will enable a broader range of novel (exo)planetary observations as well as galactic and extragalactic studies. Here we present the science cases that drive the design of SCALES. We describe an end-to-end instrument simulator that we use to track requirements and show simulations of expected science yields for each driving science case. We conclude with a discussion of preparations for early science when the instrument sees first light in approximately 2025.

SCALES is a 2 -5 micron, high-contrast, lenslet-based, integral field spectrograph (IFS) designed to characterize exoplanets and their atmospheres. In this proceeding, we present the updated design and current status of the SCALES slenslit, a novel take on an image slicer. The slenslit optics, which are being fabricated by Durham University’s Precision Optics group, dissect and rearrange a subset of lenslet micro-pupils into a pseudo-slit. The pseudo-slit is then dispersed with much higher spectral resolution than other lenslet-based IFS instruments. The slenslit technology opens new vistas for the characterization of exoplanet formation environments and atmospheres by improving the spectral resolution while maintaining the diffraction-limited imaging.

The SCALES instrument is a high-contrast imager and integral field spectrograph that operates in the infrared region and is intended to be utilized behind the W.M. Keck Observatory's adaptive optics system. The SCALES integral field spectrograph operates over a broad wavelength range from 2.0 to 5.0 µm. The instrument includes a microlens array-based integral field spectrograph that, when combined with a lenslet to slicer reformatter referred to as "slenslit," allows for low (R = 35 - 250) and moderate (R = 2000 - 6500) spectral resolution spectroscopy. We have done extensive end-to-end modeling of the SCALES optical path using both geometric optics and physical optics. This analysis has been vital in predicting both spectral format and optical performance. We have also combined the predicted geometric point spread function (PSF) given a complete end-to-end system including the SCALES lenslet array IFU, with modeled diffraction effects to understand the crosstalk between the spectra. The PSF modeling is being integrated with the SCALES instrument simulator to provide realistic data products that are being used to develop the SCALES data pipeline.

Combined light High-Resolution Cross-Correlation Spectroscopy (HRCCS) uses cross-correlation with a model planetary atmosphere to identify/isolate spectral features that show a Doppler shift consistent with the motion of a close-in exoplanet. This technique can be used to retrieve molecular abundances and pressure-temperature profiles for hot Jupiters, offering insight into planet formation and atmospheric chemistry. HRCCS is quite sensitive to instrumental systematics, in particular shifts in wavelength solution, blaze function variation, uncorrected tellurics, and fringing. We discuss the on-sky performance of Keck/KPIC for HRCCS, with a focus on the impact of these systematic effects and mitigation approaches.

HISPEC is a new, high-resolution near-infrared spectrograph being designed for the W.M. Keck II telescope. By offering single-shot, R 100,000 spectroscopy between 0.98 – 2.5 μm, HISPEC will enable spectroscopy of transiting and non-transiting exoplanets in close orbits, direct high-contrast detection and spectroscopy of spatially separated substellar companions, and exoplanet dynamical mass and orbit measurements using precision radial velocity monitoring calibrated with a suite of state-of-the-art absolute and relative wavelength references. MODHIS is the counterpart to HISPEC for the Thirty Meter Telescope and is being developed in parallel with similar scientific goals. In this proceeding, we provide a brief overview of the current design of both instruments, and the requirements for the two spectrographs as guided by the scientific goals for each. We then outline the current science case for HISPEC and MODHIS, with focuses on the science enabled for exoplanet discovery and characterization. We also provide updated sensitivity curves for both instruments, in terms of both signal-to-noise ratio and predicted radial velocity precision.

The upcoming Extremely Large Telescopes have the angular resolution and light collecting area that is necessary to observe biosignatures in the atmospheres of Earth-like planets. High-contrast imaging instruments will play a large role in this because observing planets directly overcomes many of the observational limitations of other exoplanet detection techniques. The influence of the bright star can be significantly reduced by spatially resolving the dim planet, allowing characterization of the planet and its atmosphere. However, the required wavefront sensing, and control (WFS&C) technologies have yet to be proven on-sky. The Magellan Adaptive Optics eXtreme (MagAO-X) instrument is a new visible to near-infrared high-contrast imaging system that operates as a testbed for the development and testing of WFS&C techniques.

The upcoming era of Extremely Large Telescopes will result in a significant increase in extrasolar planets detectable by direct imaging. Advances in wavefront sensing and control as well as coronagraphic technologies are necessary to achieve the contrasts and image quality required for detection on ground-based instruments. The Extreme Adaptive Optics Instrument for the Magellan Clay 6.5 m telescope (MagAO-X) serves as a testbed for ground-based adaptive optics and high contrast imaging technology development, working in the visible to near-IR. MagAO-X employs a primary wavefront control loop to correct for high order wavefront errors resulting from atmospheric turbulence. A secondary loop has been implemented for correcting non-common path aberrations and has shown to improve overall system and coronagraphic performance.

Here we describe the architecture of a compact adaptive optics system that is designed specifically to couple light into a single-mode optical fiber. The dramatic reduction in size of this instrument is afforded by the reduction in pupil size by MEMs deformable mirrors. Or system also enables fast tip/tilt control as well as atmospheric dispersion correction – necessary for extended sky coverage. The heritage and architecture of this instrument will be described. We will also cover performance modeling, and status of the hardware and software build. We will describe our plans to couple AO systems with spectrometers to enable dramatically increased stability with implications for extreme precision radial velocity needed for the detection of exoEarths.

A few years ago, we started upgrading AO188 into AO3k, including the real-time control system, laser guide star system, Deformable Mirror (DM), and Wavefront Sensors (WFSs). In this paper, we present the development of a non-linear Curvature WFS (nlCWFS) as a new visible WFS for the upgraded AO3k system. We also introduce the optical and optomechanical design of the nlCWFS. The nlCWFS has two new features: one is the dual-stroke linear mode, and the other one is to deploy non-linear wavefront reconstruction. The dual-stroke linear mode provides a good sensitivity for both low- and high-order aberrations. Also, the non-linear wavefront reconstruction provides a large dynamic range. By combining the linear and non-linear methods, the nlCWFS takes both advantages. Finally, we present laboratory demonstration results of closed-loop experiments in the lab with linear and non-linear wavefront reconstruction algorithms.

Maintaining the co-phasing of the primary mirror segments is a critical aspect to the operation of segmented telescopes. However, speckle-based measurements of the phasing of the Keck primary estimated static aberrations of approximately 90 nm rms that are not sensed by the current edge-sensing segment control system. We propose directly sensing and controlling the primary via the wavefront sensor of the adaptive optics system, as a Controllable Segmented Primary (CSP), to actively correct its phasing. In this work, we consider strategies for implementing and calibrating the CSP system on-sky.

Various types of high-contrast imaging instruments have been proposed and developed for direct detection of exoplanets by suppressing nearby stellar light. Stellar speckles due to wavefront aberration can be suppressed by the appropriate wavefront control, called the dark hole control. However, the speckles, which fluctuate faster than the dark hole control due to atmospheric turbulence in ground-based telescopes or instrument deformation caused by temperature changes in space telescopes, cannot be suppressed by the control and remain in focal plane images. The Coherent Differential Imaging on Speckle Area Nulling (CDI-SAN) method was proposed to overcome such fast fluctuating speckles and detect exoplanetary light. We constructed an optical setup in a laboratory to demonstrate the CDI-SAN method. With the dark hole control and the CDI-SAN method, we achieved 10⁻⁸ level of contrasts.

As we look to the next generation of adaptive optics systems, now is the time to develop and explore the technologies that will allow us to image rocky Earth-like planets; wavefront control algorithms are not only a crucial component of these systems but can benefit our adaptive optics systems without requiring increased detector speed and sensitivity or more effective and efficient deformable mirrors. To date, most observatories run the workhorse of their wavefront control as a classic integral controller, which estimates a correction from wavefront sensor residuals, and attempts to apply that correction as fast as possible in closed-loop. An integrator of this nature fails to address temporal lag errors that evolve over scales faster than the correction time, as well as vibrations or dynamic errors within the system that are not encapsulated in the wavefront sensor residuals; these errors impact high contrast imaging systems with complex coronagraphs. With the rise in popularity of machine learning, many are investigating applying modern machine learning methods to wavefront control. Furthermore, many linear implementations of machine learning methods (under varying aliases) have been in development for wavefront control for the last 30-odd years. With this work we define machine learning in its simplest terms, explore the most common machine learning methods applied in the context of this problem, and present a review of the literature concerning novel machine learning approaches to wavefront control.

The PICTURE-C balloon mission launched on its second flight from Fort Sumner, NM on September 28, 2022. During this flight, PICTURE-C, which consists of a 60 cm off-axis telescope feeding a vector vortex coronagraph, demonstrated the first high-contrast dark hole from an observatory in a near-space environment. The coronagraph achieved a modest broadband (20%) contrast ratio of 5 x 10^-6 , with performance limited by dynamic pointing transients. The low-order wavefront control system achieved optical pointing stabilization of one milliarcseconds RMS for intervals of up to 30 seconds between these transients. This paper will summarize the second flight results and present the development path for PICTURE-D, the next generation direct imaging balloon mission.

Astrophysical research into exoplanets has delivered thousands of confirmed planets orbiting distant stars. These planets span a wide range of size and composition, with diversity also being the hallmark of system configurations, the great majority of which do not resemble our own solar system. Unfortunately, only a handful of the known planets have been characterized spectroscopically thus far, leaving a gaping void in our understanding of planetary formation processes and planetary types. To make progress, astronomers studying exoplanets will need new and innovative technical solutions. Astrophotonics – an emerging field focused on the application of photonic technologies to observational astronomy – provides one promising avenue forward. In this paper we discuss various astrophotonic technologies that could aid in the detection and subsequent characterization of planets and in particular themes leading towards the detection of extraterrestrial life.

FIRST is a post Extreme Adaptive-Optics (ExAO) spectro-interferometer operating in the Visible (600-800 nm, R∼400). Its exquisite angular resolution (a sensitivity analysis of on-sky data shows that bright companions can be detected down to 0.25λ/D) combined with its sensitivity to pupil phase discontinuities (from a few nm up to dozens of microns) makes FIRST an ideal self-calibrated solution for enabling exoplanet detection and characterization in the future. We present the latest on-sky results along with recent upgrades, including the integration and on-sky test of a new spectrograph (R∼3,600) optimized for the detection of Hα emission from young exoplanets accreting matter.

Coronagraphs allow for faint off-axis exoplanets to be observed, but are limited to angular separations greater than a few beam widths. Accessing closer-in separations would greatly increase the expected number of detectable planets, which scales inversely with the inner working angle. The Photonic Lantern Nuller (PLN) is an instrument concept designed to characterize exoplanets within a single beam-width, using a device called the Mode-Selective Photonic Lantern (MSPL), a photonic mode-converter that maps linearly polarized modes into individual single-mode outputs. The PLN leverages the spatial symmetry of an MSPL to create nulled ports, which cancel out on-axis starlight but allow off-axis exoplanet light to couple. However, the quality of the nulls is dependent on the symmetry of the lantern modes, which affects how well the starlight can be suppressed. We present results from our laboratory characterization of an MSPL, including measurements of lantern port throughputs (60-90%), images of the mode intensities, and reconstructions of the mode electric fields using off-axis holography. We discuss the implications on the level of starlight suppression that this MSPL can achieve.

The Photonic Lantern (PL) is a novel optical technology consisting of a multi-mode fiber adiabatically merged to several single-mode fibers. PLs efficiently split light into its individual modes, revealing both phase and amplitude information. This makes them attractive for use in focal plane wavefront sensing and spectroscopy. Spectro-astrometry, a technique that involves searching for wavelength-dependent centroid shifts in spectrally-dispersed datasets, can be conducted with PLs to resolve circumstellar structures with extremely small angular separations that are not accessible with traditional imaging techniques. Here, we investigate the application of PLs for spectro-astrometry of young stars hosting protoplanetary disks with embedded accreting planets. Although spectro-astrometry of point-source accreting companions with PLs has been numerically explored in the past, those simulations did not include the effects of scattered light by the protoplanetary disk. We carry out numerical simulations of accretion signatures inside protoplanetary disks to understand the feasibility of using PLs to detect accreting planets under realistic conditions. We simulate the response of a 6 port PL to young stars with a circumstellar disk containing an accretion hotspot centered on the Paschen beta hydrogen line. We discuss the lower limit of the hotspot-to-star contrast detectable by a PL in the context of contamination by disk signals after introducing both random and systematic noise sources. The simulations also demonstrate the effects of scattered light by the circumstellar disk on the PL response to an embedded accreting protoplanet with a fixed planet-to-star contrast.

Photonic Lanterns (PLs) are tapered waveguides that can efficiently couple multi-mode telescope light into a multi-mode fiber entrance at the focal plane and coherently convert it into multiple single-mode beams. Each SMF samples its unique mode (lantern mode) of the telescope light in the pupil, analogous to subapertures in aperture mask interferometry. In this study, we show the concept and potential of coherent imaging with PLs. It can be enabled by interfering SMF outputs and applying path length modulation, which can be achieved using a photonic chip beam combiner at the backend (e.g., the ABCD beam combiner). Using numerically simulated lantern modes of a six-port PL, we calculate interferometric observables for various input scenes. Our simulated observations suggest that PLs may offer significant benefits in the photon-noise limited regime and for resolving small-scale (⪅ λ/2D) asymmetries.

Ground-based exoplanet science relies on the correction of aberrations induced by both atmosphere and instrument. However, current pupil-plane adaptive optics faces two major challenges: non-common-path aberrations and petaling modes. One solution is to add a wavefront sensor which operates in the focal plane, such as a photonic lantern (PL), a waveguide that efficiently couples aberrated light into single-mode fibers. We present a first experimental verification of real-time closed-loop control with the photonic lantern wavefront sensor (PLWFS), using a linear phase-retrieval algorithm, and on-sky demonstrations. We also discuss non-linear reconstruction using a neural network, and consider potentials for spectrally dispersed sensing.

Vortex Fiber Nulling (VFN) is a technique for suppressing starlight to observe exoplanets at small angular separations from their star, ≲ 1λ/D. This technique may enable the discovery and characterization of young giant planets at separations smaller than conventional coronagraphs can reach. A VFN mode was deployed to the Keck Planet Imager and Characterizer (KPIC) instrument at the Keck II telescope in February 2022 and is now operational on-sky. This marks the first on-sky demonstration of VFN. The mode has achieved on-sky starlight rejection of ⪅ 1 × 10⁻² in K-band and is primarily limited by residual wavefront error from the adaptive optics system. The current VFN performance enables KPIC to efficiently search for new companions at separations of 20 to 80 mas from their host star whereas the alternative observing mode requires precise, prior knowledge of the companion position. Here we present the latest results from the KPIC VFN mode. We also present the predicted performance improvement from an upcoming upgrade to switch the current charge two vortex mask with a new charge one which can target smaller separations and will double the planet throughput.

Vortex Fiber Nulling (VFN) is a new interferometric technique with the potential to unlock the ability to detect and spectroscopically characterize exoplanets at angular separations smaller than the conventional diffraction limit of λ/D. In early 2022, a VFN mode was added to the Keck Planet Imager and Characterizer (KPIC) instrument suite on Keck II. VFN operates by adding an azimuthal phase ramp to the incident wavefront so that light from the star at the center of the field is prevented from coupling into a single-mode fiber. One of the key performance goals of VFN is to minimize the ratio of on-axis starlight coupling to off-axis planet coupling, which requires minimizing the wavefront aberrations of light being injected into the fiber. Non-common path aberrations can be calibrated during the daytime and compensated for with the KPIC deformable mirror during nighttime observing. By applying different amplitudes of low-order Zernike modes, we determine which combinations maximize the system performance. Here we present our work developing and testing different procedures to estimate the incident aberrations, both in simulation and on the Keck bench. The current iteration of this calibration algorithm has been used successfully for VFN observing, and there are several avenues for improvement.

Kernel Phase Interferometry (KPI) is a data processing technique which enhances the angular resolution achievable by a conventional telescope in space or behind a powerful adaptive optics system. KPI is increasingly being applied to observations of young stars, which often host circumstellar disks with complex structure. Since such observations rely on fitting to an interferometric observable (the kernel phase), developing a flexible modelling approach in the form of an image reconstruction code would be greatly beneficial for recovering complex asymmetries. Here we present a proof-of-concept for such an image reconstructor that makes use of automatic differentiation to compute a gradient and Stochastic Gradient Descent (SGD) to find the best fitting image. Using simulated signals, we show that this approach works well for the case of a point-like companion but requires further development to robustly recover extended emission from a disk. This may be made possible by adding one of the many commonly applied regularizers for long-baseline or aperture masking image reconstruction and implementing a more sophisticated variant of gradient descent. Nevertheless, this simple combination of automatic differentiation and SGD shows promise for being a powerful addition to the KPI toolbox.

As exoplanet direct imaging progresses towards lower planet-star contrasts and smaller, less separated planets, the need for technological improvement in imaging systems remains ever present. Metasurface optics, or arrays of subwavelength structures with highly tailorable geometry and composition on a thin substrate, have the potential to greatly advance coronagraph systems at various stages of the optical pipeline by correcting aberrations induced by other optical components and improving upon the performance of the conventional optics that are currently used. Metasurfaces can provide achromatic phase, amplitude, and/or polarization control in a compact package. Polarization insensitive phase control devices are of particular interest, because such scalar devices are less sensitive to the polarization aberrations that can negatively impact vector optics, which are currently more prevalent in coronagraph systems. Our work provides a general overview of metasurface optics and addresses the specific application of scalar-vortex (MSV) phase masks for vortex coronagraphy and vortex fiber nulling (VFN). We detail a multi-shape, variable period design process which we use to develop MSVs of various topological charge. The MSVs we developed include a J and V band charge-6, an H-band charge-2, and a K-band charge-1 MSV. The J, H, K, and V devices exhibit achromatic behavior over 15%, 12%, a 11%, and a 24% bandwidth, respectively. We also develop a multiplexed vector vortex-phase dimple metasurface for the H-band as a showcase of another way in which metasurfaces can advance direct imaging systems. We demonstrate simulated K-band MSV performance in the Keck Observatory VFN instrument with on-axis coupling below 10−3 . We detail the path to a MSV that can achieve contrasts that will enable the imaging of terrestrial planets.

Imaging Earth-like planets around sun-like stars has become one of the main science drivers for future space telescope missions. High-contrast imaging using a vortex coronagraph has proven to be a promising approach for achieving this goal. However, at the huge contrast levels required for future space-based telescopes the vectorial nature of the well-established vector vortex phase mask becomes a limiting factor, since it imprints phase ramps of opposite signs on the two circular polarizations. An alternative polarization-independent approach is using a scalar vortex phase mask, which affects both polarizations in the same way. The achromatic performance of scalar vortex phase masks for space-based applications has still to be improved, though. Metasurfaces provide a promising approach to implement a scalar vortex phase mask with relatively simple fabrication techniques. Their demonstrated ability to implement broadband phase and amplitude masks makes them a prime candidate for achieving achromatic performance in pursuit of the 10⁻¹⁰ contrast limit required by NASA’s Habitable Worlds Observatory. We present a metasurface-based design of a scalar vortex phase mask providing a helical phase ramp across a large bandwidth. We first use rigorous coupled-wave analysis to create a library of square metasurface building blocks (nanoblocks) and choose an optimal set of nanoblock sizes providing broadband 2π phase coverage at a given nanoblock height. We then arrange the nanoblocks in a design providing a helical phase ramp and propagate the phase and transmission provided by the mask through a wavefront propagation software to obtain contrast curves at several wavelengths. Finally we apply electric field conjugation to dig a half-sided dark hole from 3-10 λ/D reaching 3.7 × 10⁻⁹ contrast in 20% bandwidth.

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 10⁻¹⁰. 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.

The Visible Aperture Masking Polarimetric Imager for Resolved Exoplanetary Structures (VAMPIRES) is a visible light instrument on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system. To characterize the Instrumental Polarization (IP) and crosstalk of the system, measurements with a polarized internal calibration source were taken to provide diattenuation and retardance estimates of components downstream of the telescope mirrors. Using Markov Chain Monte Carlo (MCMC) simulations, we developed a Mueller matrix model of VAMPIRES in five wavelength bands. The process of deriving the model revealed degeneracies involving multiple possible sets of values for highly correlated instrument parameters. It also revealed a significant difference in the EM gain ratio between VAMPIRES’ two cameras and the highly non-ideal behavior of the Ferroelectric Liquid Crystal (FLC). Observations of unpolarized and polarized standard stars from two separate nights have been collected and are currently being analyzed to provide an estimate of M3’s diattenuation and retardance as well, and the polarized standard stars in particular will be used as a final metric to quantify the instrument model’s accuracy. The current Mueller matrix model has already been applied to preliminary data analysis for the circumstellar disk HD34700 and has helped confirm that an observed 17° phase shift in differential visibilities for Mu Cephei is astrophysical in nature. The non-ideal behaviour of certain components highlights the need for a standard calibration procedure that should be performed regularly to track changes in VAMPIRES’ polarization qualities. Our laboratory and on-sky data collection and analysis procedures will be refined to be re-used to calibrate future versions of VAMPIRES, including its most recent upgrade in 2023.

The Nancy Grace Roman Space Telescope Coronagraph Instrument is a critical technology demonstrator for NASA’s Habitable Worlds Observatory. With a predicted visible-light flux ratio detection limit of 10⁻⁸ or better, it will be capable of reaching new areas of parameter space for both gas giant exoplanets and circumstellar disks. It is in the final stages of integration and test at the Jet Propulsion Laboratory, with an anticipated delivery to payload integration in the coming year. This paper will review the instrument systems, observing modes, potential observing applications, and overall progress toward instrument integration and test.

The Roman Space Telescope will be launched in a few years, and its Coronagraphic Instrument (CGI) is being assembled after a decade of development. The on-orbit performance of CGI has been predicted using numerical modeling, including diffraction and wavefront control modeling to simulate images and finite element modeling to estimate wavefront instabilities due to thermal and vibrational (reaction wheels) disturbances. We describe the final end-to-end modeling results representing a realistic observing scenario.

The Coronagraph Instrument of the Nancy Grace Roman Space Telescope (Roman Coronagraph) will be capable of both total intensity and polarization measurements of circumstellar disks. The polarimetric performance is impacted by polarization effects introduced by all mirrors before the Wollaston prisms. In this paper, we aim to characterize these effects for the Roman Coronagraph in bands one and four using the FALCO and PROPER packages. We simulate the effect of polarization aberrations that impact the polarimetric contrast and the instrumental polarization effects to study the polarimetric accuracy. We include spacecraft rolls but leave out systematic camera noise. We find that Polarimetric Differential Imaging (PDI) improves the contrast by a factor of six. The PDI contrast of ∼ 8 × 10⁻¹¹ is limited by polarized speckles from instrumental polarization effects and polarization aberrations. By injecting polarized companions with at various contrast levels and demodulating their polarimetric signal, we recover their source Stokes vector within 2%.

The Nancy Grace Roman Space Telescope Coronagraph Instrument (CGI) will demonstrate spectroscopy of planets and polarization measurements of disks. The spectroscopy and polarization modes utilize Amici and Wollaston prism designs. The spectroscopy mode, designed and built and Goddard Space Flight Center (GSFC), has a resolution of R50 in 15% bands centered at 660nm and 730nm. The Wollaston design and optics are contributed by the Japanese Aerospace Exploration Agency, with final alignment and testing at GSFC. We present the requirements, ground-to-orbit calibration, and deployable slit operations. We also detail on the design, results from the as-built flight assemblies.

This conference presentation was prepared for SPIE Optical Engineering + Applications, 2023.

The Astro2020 decadal survey recommended the Habitable Worlds Observatory (HWO), NASA’s direct imaging flagship mission, with a goal to achieve a statistically robust mission yield of 25 or more potentially habitable exoplanets. One way to achieve is to increase the instrument effectiveness by introducing additional bright, nearby targets. A majority of Sun-like stars have a stellar companion that can introduce additional noise into the field of view of any high-contrast imaging instrument and enabling exoplanet discovery around binary stars represents a path to increased coronagraphic instrument efficiency by increasing the available science target pool of bright nearby stars. This includes both of the Alpha Centauri A and B stars which would represent the top science target for direct imaging if companion leakage could be suppressed. Multi-Star Wavefront Control (MSWC) is a technique that removes stellar leakage from both stellar components, enabling direct imaging of exoplanets in many binary star systems which can potentially increase coronagraphic instrument effectiveness We present the latest testbed results obtained with MSWC as part of the technology development effort focusing on demonstrations conducted on the Occulting Mask Coronagraph (OMC) testbed at JPL during the vacuum test window last winter, with an additional vacuum test planned for this fall. The MSWC mask consists of a shaped pupil mask similar to the one used for the Wide-Field of View mode, but also includes a set of superimposed, regularly spaced dots that serve as a diffraction grating. OMC has a layout similar to the Roman Space Telescope coronagraph instrument and configured with a binary imaging mode with a MSWC mask using same design as the contributed mask for the Roman coronagraph. Our testbed results represent the first demonstrations of this technique using the recently installed full binary source. We present results demonstrating suppression in the Super-Nyquist regime for the third diffraction order reaching 8.7e-9 contrast with the Roman pupil. In addition, we present results obtained with a physical binary source and running MSWC in a binary star regime demonstrating 9.6e-8 contrast for a geometry matching potential Alpha Centauri observations in a 515 nm monochromatic wavelength (similar but bluer than for Band one) using the fifth diffraction order. Planned demonstrations in the upcoming vacuum window this fall will focus on Band 3d and Band 4 using the full MSWC mode for an Alpha Centauri geometry.

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 ζ 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 ζ 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.

The Habitable Worlds Observatory (HWO) concept is a 6-meter diameter deep space telescope operating from the ultraviolet through the near infrared. One of its primary goals is to measure the spectra of 25 Earth-like exoplanets. While the Decadal Survey described a highly stabilized off-axis telescope with a coronagraph to perform these measurements, a starshade offers an alternative approach that will be especially effective in the ultraviolet because it offers high throughput, large bandwidth, small working angle, and does not require a picometer-stabilized telescope. We show the feasibility of obtaining UV spectra and measuring the presence of Ozone in the Hartley band using a 35 m diameter starshade with a bandpass of 250 nm to 500 nm. Spectra with high SNR can be obtained in just a few days of integration on Earth-like exoplanets orbiting solar type stars.

The optical edges of a starshade define its outermost perimeter. During astronomical measurements, the edges are exposed to sunlight resulting in glint seen by the telescope. Clean, sharply etched edges are capable of meeting the stringent solar glint scatter requirement. We report on the increased glint that arises from particulate contamination clinging to the edges. We measure the relationship between surface contamination and edge contamination and compare to a simple edge contaminant population model where the edge acts like a line drawn across the continuous surface. We correlate the level of edge contamination to the degree of increased scatter and derive an on-orbit contamination requirement that is compatible with the detection of exo-Earths.

Deformable Mirrors (DMs) are at the heart of any adaptive optics system. State-of-the-art, high-actuator count DMs suffer from external heavy and bulky electronics in which electrical connections are made through thousands of wires. To overcome this challenge, we are developing Application Specific Integrated Circuits (ASIC) capable of driving a DM in a single small package in space conditions. This integrated ASIC-DM is ideal for space missions, where it offers significant reduction in mass, power and complexity while maintaining performance compatible with high-contrast imaging of exoplanets. We successfully prototyped, package and tested a 16x16 DM-ASIC array following the Roman Space Telescope mission requirements. The ASIC chip was irradiated to a total ionizing dose equivalent to a six-year mission in L2 orbit and tested at the Roman coronagraph specific temperature range.

The Exoplanet Spectroscopy (ExoSpec) project links four different tasks at Goddard Space Flight Center (GSFC) to facilitate efficient imaging and characterization of exoplanets. One of the tasks is the development of parabolic deformable mirrors to improve on the current state-of-the-art wavefront sensing and control implementations that are baselined to have two high-actuator count flat Deformable Mirrors (DMs). The current baseline has two DMs at a considerable separation distance to effectively control both amplitude and phase aberrations. This significant separation poses packaging challenges to the direct imaging missions. We can mitigate this issue by making the off-axis imaging elements in the optical train controllable. Besides addressing the packaging challenges, this technique reduces the risk of having the entire coronagraph instrument’s performance depend on two high-actuator count DMs. Simulations show that making imaging elements deformable increases the overall controllable bandwidth - it would be possible to control wavefront aberrations up to 35% bandwidth over a 5 - 12 λ|D. GSFC has worked with a commercial vendor to produce a first-generation parabolic DM and built a testbed in an environmentally controlled cleanroom to experimentally demonstrate the use of a parabolic DM in a coronagraph instrument. This versatile testbed is designed to test different DM architectures and various low-order wavefront schemes. This provides us with a basis for comparison with different DM configurations: 1) flat DM, 2) parabolic DMs, and 3) flat DM and parabolic DMs. In this paper, we will provide an update on our parabolic DM work.

The Gemini Planet Imager’s performance was limited by speckle noise from post-coronagraph aberrations and internal optical imperfections. As part of the GPI 2.0 calibration unit upgrade, we demonstrate closed loop focal plane wavefront sensing and control techniques to enable higher contrast and smaller inner working angles. We present the experimental results of the classical speckle nulling method on a self-coherent camera, with contrast improvement by up to a factor of 3.2.

Coronagraphic instruments provide a great chance of enabling high contrast spectroscopy for the pursuit of finding a habitable world. Future space telescope coronagraph instruments require high performing focal plane masks in combination with precise wavefront sensing and control techniques to achieve dark holes for planet detection. Several wavefront control algorithms have been developed in recent years that might vary in performance depending on the coronagraph they are paired with. This study compares three model-free and model-based algorithms when coupled with either a Vector (VVC) or a Scalar (SVC) Vortex Coronagraph mask in the same laboratory conditions: Pairwise Probing with Electric Field Conjugation, the Self-Coherent Camera with Electric Field Conjugation, and Implicit Electric Field Conjugation. We present experimental results from the In-Air Coronagraph Testbed (IACT) at JPL in narrowband and broadband light, comparing the pros and cons of each of these wavefront sensing and control algorithms with respect to their potential for future space telescopes.

Due to the reporting from the Astro2020: Decadal Survey for Astronomy and Astrophysics, the direct imaging of Earth-like exoplanets has become a leading priority for research and development in astrophysics. In response to this survey, NASA has selected the Habitable Worlds Observatory (HWO) as its next astrophysics flagship mission. However, the current state-of-the-art coronagraph technology is not sufficient to achieve the required contrast (approximately 10⁻¹⁰) with HWO’s proposed configuration. Improving the technology readiness level of coronagraphs for HWO will require extensive research and development. To increase its capacity to support this objective and to provide the community with a new resource to perform versatile coronagraph technology development, NASA’s High Contrast Imaging Testbed (HCIT) facility at the Jet Propulsion Laboratory (JPL) has commissioned the Decadal Survey Testbed 2 (DST2), a state-of-the-art vacuum coronagraph testbed. It’s commissioned architecture incorporates a 2K-actuator Boston Micromachines deformable mirror and a traditional Lyot coronagraph and features a flexible design capable of accommodating different coronagraph technologies including tip/tilt mirrors, segmented apertures, reflective pupils, disturbance injection, wavefront sensing and control, and the integration of additional sources or telescope simulators with minimal reconfiguration. DST2 has repeatably achieved 1 × 10⁻⁹ monochromatic raw contrast, and 3.3 × 10⁻⁹ raw contrast in a 10% bandwidth centered at 550nm in a 180 degree dark hole from 3λ/D to 9λ/D. Additionally, DST2 uses new 20-bit DM electronics capable of a 650 femtometer DM actuator resolution which meets future requirements for HWO. As of August 2023, DST2 has begun operations to meet scientific milestones set by the principal investigators of NASA Strategic Astrophysics Technologies awards. Parallel to these priorities, work to determine contrast limitations will be performed.

Directly imaging Earth-sized exoplanets with a visible-light coronagraph instrument on a space telescope will require a system that can achieve approximately 10⁻¹⁰ raw contrast and maintain it for the duration of observations (on the order of hours or more). We are designing, manufacturing, and testing Dual Purpose Lyot coronagraph (DPLC) masks that allow for simultaneous wavefront sensing and control using out-of-band light to maintain high contrast in the science focal plane. Our initial design uses a tiered metallic focal plane occultor to suppress starlight in the transmitted coronagraph channel and a dichroic-coated substrate to reflect out-of-band light to a wavefront sensing camera. The occultor design introduces a phase shift such that the reflected channel is a Zernike wavefront sensor. The dichroic coating allows higher-order wavefront errors to be detected which is especially critical for compensating for residual drifts from an actively-controlled segmented primary mirror. A second-generation design concept includes a metasurface to create polarization-dependent phase shifts in the reflected beam, which has several advantages including an extended dynamic range. We will present the focal plane mask designs, characterization, and initial testing at NASA’s High Contrast Imaging Testbed (HCIT) facility

The planned Habitable Worlds Observatory (HWO) will be designed to find and characterize Earth-like planets in the habitable zones of sun-like stars. This mission will require an instrument capable of making measurements of planet spectra at high contrast and small inner working angles. Previous demonstrations of existing coronagraph designs have not achieved these requirements at the 20% bandwidths or better required for full spectroscopic characterization, even in a laboratory environment. One technique that shows promise for improving bandwidth is the allocation of Deformable Mirror (DM) degrees of freedom to improve bandwidth by relaxing requirements on the size of the coronagraph’s focal plane correction region, or Dark Zone (DZ). In this work, we provide details and results of a laboratory demonstration of a wide-band coronagraph in NASA’s High-Contrast Imaging Testbed (HCIT) at the Jet Propulsion Laboratory (JPL). We show that a D-shaped region on one half of the focal plane can be corrected to a contrast of 4×10⁻¹⁰ in a 20% bandwidth using a simple Lyot coronagraph with two DMs. We also provide details of future plans to improve contrast and bandwidth by further reducing the dark region to just the light coupled into a single-mode fiber in the coronagraph’s focal plane.

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.

The High Contrast Spectroscopy Testbed (HCST) in the Exoplanet Technology laboratory (ETlab) at Caltech is an in-air testbed hosting all key components necessary to demonstrate coronagraphic performance in broadband light with the vortex coronagraph. The testbed was recently upgraded with the aim of closing the remaining technological gaps in terms of pupil segmentation and to demonstrate our main objective: achieving 10⁻⁸ contrast in broadband light. As part of the HCST redesign, a new apodizer has been manufactured using carbon nanotubes acting as microdots to encode a grayscale pattern. This technology presents a very low reflectance conducive to highly efficient amplitude apodization. We demonstrate raw contrasts of 1 × 10⁻⁸ with the apodized vortex coronagraph, both in narrowband and broadband light (10% bandwidth), and with the use of wavefront control. The use of an apodizer enables to deal with the diffraction caused by the segment gaps and successfully eliminates this source of starlight leakage for the vortex coronagraph to the 10⁻⁸ level.

A pathway to maximizing the scientific yield of future exoplanet imaging instruments is to develop technologies that give access to high levels of contrast over large bandwidths. Combining the use of Deformable Mirrors (DMs) for wavefront control and a Single Mode Fiber (SMF) in the image plane has been proven to enhance the contrast achievable for broadband characterization of exoplanet atmospheres. Indeed, the modal selectivity of the SMF aids with the rejection of speckles in the vicinity of the companion. Furthermore, the stroke requirements on the DMs needed to achieve high levels of raw contrast are relaxed given the reduced spatial frequencies needed. Here we report on the status of our SMF wavefront control experiments at the High-Contrast Spectroscopy Testbed (HCST) in the Exoplanet Technology Laboratory at Caltech: we have reached 1×10⁻⁸ raw contrast over 20% bandwidth with an SMF.

The phase-apodized-pupil Lyot coronagraph (PAPLC) produces a one-sided dark zone, with, in theory, a 2 λ/D inner working angle at contrasts of 10^-10 and high planet throughput, perfect for future space missions such as the Habitable Worlds Observatory. The two DMs in the wavefront control system serve as the apodizer. We present laboratory results on a segmented telescope pupil in broadband light on the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed. A Zernike wavefront sensor, which uses the light rejected by the coronagraph, simultaneously measures any high-order aberrations. We report on the achieved broadband contrast within a 10% and 20% bandpass, under natural and artificial environmental conditions.

In recent work, we numerically and experimentally demonstrated a new approach to high-contrast wavefront control based on the combination of nonlinear optimization with algorithmic differentiation, which we termed Algorithmic Differentiation Wavefront Control (ADWC). ADWC is more computationally efficient than Jacobian-based control algorithms for Deformable Mirror (DM) actuator counts and focal plane sizes relevant to the planned Habitable Worlds Observatory, which potentially opens a path toward on-orbit wavefront sensing and control. Here, we review these results with a view toward their potential impact on NASA’s planned Habitable Worlds Observatory and describe ongoing simulations and experiments, including extensions to adaptive control.

We report on experimental stabilization of low-order aberrations on a high-contrast testbed for exoplanet imaging, in up to 10% broadband light under natural and artificial drifts. The measurements are performed with a Zernike wavefront sensor using the light rejected by the focal plane mask of an apodized Lyot coronagraph. We conduct the experiments on the High-contrast imager for Complex Aperture Telescopes testbed, with a segmented aperture and two continuous deformable mirrors. We study several use cases, from the stabilization of a pre-established dark hole to the concurrent combination with focal-plane wavefront sensing in the form of sequential pairwise sensing over several wavelengths.

In order to directly image Earth-like exoplanets (exoEarths) orbiting Sun-like stars, the Habitable Worlds Observatory coronagraph instrument(s) will be required to suppress the starlight to raw contrasts of approximately 10⁻¹⁰ . Coronagraphs use active methods of Wavefront Sensing and Control (WFSC) such as Pairwise Probing (PWP) and Electric Field Conjugation (EFC) to create regions of high contrast in the science camera image, called dark holes. Due to the low flux of these exoEarths, long exposure times are required to spectrally characterize them. During these long exposures, the optical system will drift resulting in degradation of the contrast over time. To prevent such contrast drift, a WFSC algorithm running in parallel to the science acquisition can stabilize the contrast in the dark hole. However, PWP cannot be reused to efficiently stabilize the contrast since it relies on strong temporal modulation of the intensity in the image plane that would interrupt the science acquisition. Conversely, spectral Linear Dark Field Control (LDFC) takes advantage of the linear relationship between the change in intensity of the post-coronagraph out-of-band image and small changes in wavefront to preserve the dark hole region during science exposures. In this paper, we show experimental results that demonstrate spectral LDFC stabilizes the contrast to levels of a few 10⁻⁹ on a Lyot coronagraph testbed which is housed in a vacuum chamber. Promising results show that spectral LDFC is able to correct for disturbances that degrade the contrast by more than 100×. To our knowledge, this is the first experimental demonstration of spectral LDFC and the first demonstration of spatial or spectral LDFC on a vacuum coronagraph testbed and at contrast levels less than 10⁻⁸ .

Accurate measurement of exoplanetary masses is a critical step in addressing key aspects of NASA’s science vision. Measuring masses of Earth-analogs around FGK stars out to 10 pc requires sub-microarcsecond astrometric accuracy, which is not within the capabilities of current instrumentation. Thus, new technology will be required to build an astrometric instrument capable of achieving such performance. This will immediately empower the possibility for dedicated astrometric missions, and perhaps most enticingly, it will enable astrometric observing modes to be added to any mission boasting a sufficiently stable direct imaging platform. In this paper, we provide an overview of the scientific goals and technology utilized on NASA’s testbeds dedicated to advancing stellar astrometry for exoplanet detection. The first one, located at the Jet Propulsion Laboratory (JPL), is dedicated to imaging stellar astrometry on sparse fields. The goal of this testbed is to mature the Diffractive Pupil technology to TRL-5, demonstrating high-fidelity performance in a relevant environment. This testbed operates in a vacuum tank at the High Contrast Imaging Testbed (HCIT) at JPL and has demonstrated detection of signals of 1.58e-5 λ/D which is equivalent to 0.75 μas on Hubble. The second testbed is also located at JPL, but it is dedicated to advancing narrow angle relative astrometry to detect exoplanets around nearby binary stars. The key technology in this testbed is a diffractive pupil specially designed to measure the angle between two sources on the sky. This testbed operates in air now, but we are designing a new version of this testbed that will operate in vacuum with the goal of demonstrating sub-microarcsecond accuracy astrometric measurements between binary stars.

Detecting the astrometric signal of exoplanets is a powerful way to determine its mass, but the small size of the signal presents a challenge. For Earth-like planets around Sun-like stars within 10 pc the signal is expected to be a microarcsecond or less. We developed an astrometry testbed to simulate equivalent signals using an illuminated pinhole array and a flexurized central pinhole with picometer resolution. The active wide-field sky simulator is the critical component in the testbed that simulates the small astrometric signals. We report its performance on measuring and correcting optical aberrations caused by thermal distortions and pointing jitter which are later calibrated by a diffractive pupil.

NASA recently announced the Habitable Worlds Observatory, a coronagraphic mission to detect rocky planets in their habitable zones, assess their habitability, and search for biosignatures. Surface liquid water is central to the definition of planetary habitability. Photometric and polarimetric phase variations are one of the main ways we expect to be able to detect oceans, via specular reflections off the surface water. The range of scattering phases accessible for an exoplanet can be limited by its orbital inclination or the coronagraph’s inner working angle. We use the list of target stars for the Habitable Worlds Observatory to estimate the number of exo-Earths that could be searched for non-Lambertian scattering phenomena. Here we will present our methodology and the relationship between inner working angle and accessible phase angles. From these results, we quantify the number of systems for which we expect to be able to detect ocean glint (and other scattering processes), as a function of the accessible inner working angle.

NASA is currently responding to the recommendations of the astrophysics decadal survey via its Great Observatories Maturation Program and preparing for the maturation of the Habitable Worlds Observatory, which will have a key science goal of exoplanet detection and characterization. An important element of this process is the evaluation of the impact of mission design decisions on mission science outcomes. One approach to such science yield modeling is via Monte Carlo Mission Simulation (MCMS) - the generation of ensembles of simulated mission schedules from which performance metric statistics can be derived. MCMS requires the ability to automatically schedule such observing sequences based on a mission concept’s stated operating rules. However, inefficiencies in the scheduler can lead to suboptimal performance and decreases in expected science yield that are not driven by any design decisions. Here, we discuss approaches to quantifying the impacts of schedulability and scheduling inefficiencies on science yields, and present a new method for validating scheduler efficiency.

The Astro2020 Decadal Survey recommended a “future large IR/O/UV telescope optimized for observing habitable exoplanets and general astrophysics” that would “search for biosignatures from a robust number of about 25 habitable zone [exo]planets,” now dubbed the Habitable Worlds Observatory (HWO). The search for biosignatures requires high quality spectra over a broad bandwidth and sufficient signal-to-noise. The combination of wavelength, spectral resolution, bandwidth, and signal-to-noise-ratio impacts the number of exo-Earths that can be spectrally characterized. Previous work (Morgan et al. 2022) evaluated the number of Earth-size, habitable zone exoplanets (denoted here as yield) that could be spectrally characterized over the wavelength range of 500 nm to 1000 nm for a 6-m diameter exoplanet direct imaging mission for coronagraph-only and hybrid coronagraph-starshade architectures for three prior knowledge cases: the nominal case of a blind-search survey, the upper-bound case of perfect prior knowledge, which is useful to determine if target depletion occurs, and the partial prior knowledge case of a hypothetical extreme precision radial velocity survey. In this paper, we extend previous exoplanet yields to include wavelengths out to 1.8 microns. Because the IWA for coronagraphs is proportional to wavelength, the achievable spectral coverage will be different for every planet detected. We present the spectral coverage achieved across individual target stars, as well as the ensemble target set, for a coronagraph-only architecture and a hybrid coronagraph + starshade architecture. We use the three prior knowledge cases. The coronagraph spectral characterization is simulated in the near infrared for each of the 10% sub-bands individually, as if it were the only spectral characterization performed during the mission, and then as a broadband spectral characterization performed in sequence over the sub-bands. The starshade achieves the broadband spectral equivalent simultaneously. We also examine the capabilities of the 60 m starshade point design and investigate the benefits of refueling.

Coronagraphic space telescopes for imaging Earth-like exoplanets, such as the projected Habitable Worlds Observatory, will require extraordinary optical stability, with wavefront drift performance measured in the picometers. This paper considers how active means, using sensing and control subsystems, can control the entire coronagraphic beam train, from the telescope’s segmented primary mirror, through the coronagraph’s deformable mirrors, to stabilize the electric field in the coronagraph. Integrated telescope and coronagraph models are used to show how this can work to preserve contrast at the 10^-10 level and provide important observational efficiencies. In future work, the models will also be used to identify needed performance levels for the various control system components, to help inform NASA’s technology funding priorities.

Future space telescopes such as the Habitable Worlds Observatory (HWO) will use coronagraphs and wavefront control to achieve the approximate 10¹⁰ starlight suppression necessary to directly image Earth-like exoplanets. Wavefront control algorithms such as Electric Field Conjugation (EFC) will control thousands of actuators at cadences of seconds or minutes. EFC uses a Jacobian matrix which maps Deformable Mirror (DM) voltages to the change in electric field at the image plane. The Jacobian matrix grows in size with the number of pixels, DM actuators, and spectral channels. EFC on proposed future telescopes like HabEx and LUVOIR will require as much as 25 GFLOPS (floating point operations per second). This level of compute density has never been achieved on radiation-hardened processors that are used on NASA Class-A missions such as the Roman Space Telescope. Previous work has focused on estimating the Compute Density (CD) of processors using assumptions about memory access characteristics and the parallelizability of algorithm implementation. Such analysis produces large uncertainty due to the assumptions necessary to compute CD. To refine the estimates of EFC compute capability of current generation processors, we determine the FLOPS performance of processors using benchmark tests which represent the operations mix and memory access patterns of EFC. The expected EFC iteration computation period on future space telescopes based on application benchmarks is reported. We have created a ray tracing optical model for the telescope assembly as well as a physical optics model for the telescope and coronagraph for the purposes of testing HOWFC algorithms. This testing can be applied to CPUs and FPGAs, representing a range of potential compute architectures.

Due to turbulence in the atmosphere images taken from ground-based telescopes become distorted. With Adaptive Optics (AO) images can be given greater clarity allowing for better observations with existing telescopes and are essential for ground-based coronagraphic exoplanet imaging instruments. A disadvantage to many AO systems is that they use sensors that cannot correct for non-common path aberrations. We have developed a new focal plane wavefront sensing technique to address this problem called Deformable Mirror (DM)-based pupil chopping. The process involves a coronagraphic or non-coronagraphic science image and a deformable mirror, which modulates the phase by applying a local tip/tilt every other frame which enables correcting for leftover aberrations in the wavefront after a conventional AO correction. We validate this technique with both simulations (for coronagraphic and non-coronagraphic images) and testing (for non-coronagraphic images) on UCSC’s Santa Cruz Extreme AO Laboratory (SEAL) testbed. We demonstrate that with as low as 250 nm of DM stroke to apply the local tip/tilt this wavefront sensor is linear for low-order Zernike modes and enables real-time control, in principle up to kHz speeds to correct for residual atmospheric turbulence.

Exoplanet imaging has thus far enabled studies of wide-orbit (⪆10 AU) giant planet (⪆2 Jupiter masses) formation and giant planet atmospheres, with future 30 meter-class Extremely Large Telescopes (ELTs) needed to image and characterize terrestrial exoplanets. However, current state-of-the-art exoplanet imaging technologies placed on ELTs would still miss the contrast required for imaging Earth-mass habitable-zone exoplanets around low-mass stars by 100x due to speckle noise–scattered starlight in the science image due to a combination of aberrations from the atmosphere after an Adaptive Optics (AO) correction and internal to the telescope and instrument. We have been developing a focal plane wavefront sensing technology called the Fast Atmospheric Self-coherent camera Technique (FAST) to address both of these issues; in this work we present the first results of simultaneous first and second stage AO wavefront sensing and control with a Shack Hartmann Wavefront Sensor (SHWFS) and FAST, respectively, using two common path deformable mirrors. We demonstrate this “multi-WFS single conjugate AO” real-time control at up to 200 Hz loop speeds on the Santa Cruz Extreme AO Laboratory (SEAL) testbed, showing a promising potential for both FAST and similar high-speed diffraction-limited second-stage wavefront sensing technologies to be deployed on current and future observatories, helping to remove speckle noise as the main limitation to ELT habitable exoplanet imaging.

The 2.1 m-telescope at Mt.Wendelstein in the German Alps will be equipped with an upgraded multi-focal station, distributing the telescope light of one of the Nasmyth ports to either a high-resolution radial velocity instrument, a Shack-Hartmann wavefront sensor or a three-channel-imager. For feeding calibration light to both, the Shack-Hartmann Sensor and the fiber-fed high-resolution spectrograph, a diffraction-limited telescope simulator is used. This simulator mimics the angular distribution of light (secondary mirror vignetting) of the telescope in order to excite the same modes in the fiber feed as the” real” telescope. This is necessary to allow for m/s calibration by means of an astro frequency comb. As 1 m/s corresponds to about 1/2000 of a 13.5 μm pixel on the R=60000 spectrograph, modal effects are crucial and small changes in the illumination of the fiber have an imprint on the calibration accuracy that can be achieved in simultaneous calibration mode. With this paper we introduce the optical layout of the telescope simulator and its opto-mechanical design, taking into account the space constraints at one of our Nasmyth ports of the telescope. The wavefront performance is verified utilizing a Shack-Hartmann sensor. And it is verified that the system is tolerant to small alignment inaccuracies allowing for a relatively relaxed co-alignment of the telescope simulator and the telescope. Our tests in the laboratory prior to installation of the telescope simulator show small wavefront errors and prove that the optical system of the telescope simulator meets all requirements, including a performance that is diffraction limited (Marechal limit: RMS ⪅ λ/14).

The detection and characterization of Earth-like exoplanets around Sun-like stars is a primary science motivation for the Habitable Worlds Observatory. However, the current best technology is not yet advanced enough to reach the 10⁻¹⁰ contrasts at close angular separations and at the same time remain insensitive to low-order aberrations, as would be required to achieve high-contrast imaging of exo-Earths. Photonic technologies could fill this gap, potentially doubling exo-Earth yield. We review current work on photonic coronagraphs and investigate the potential of hybridized designs which combine both classical coronagraph designs and photonic technologies into a single optical system. We present two possible systems. First, a hybrid solution which splits the field of view spatially such that the photonics handle light within the inner working angle and a conventional coronagraph that suppresses starlight outside it. Second, a hybrid solution where the conventional coronagraph and photonics operate in series, complementing each other and thereby loosening requirements on each subsystem. As photonic technologies continue to advance, a hybrid or fully photonic coronagraph holds great potential for future exoplanet imaging from space.

To reduce the amount of stellar light for exoplanet detection, coronagraphs feature amplitude masks in pupils plane(s) and/or focal plane(s), where a large fraction of photons are stopped -- and generally not used. Here, we give an overview of where potentially useful stellar (and circumstellar) photons are lost. We review existing concepts that use these lost photons, and propose generic strategies to make use of them for various applications. We particularly focus on wavefront sensing applications, but also explore how these photons can be used for calibration measurements, or for additional scientific observations.

Looking to the future of exo-Earth imaging from the ground, core technology developments are required in visible Extreme Adaptive Optics (ExAO) to enable the observation of atmospheric features such as oxygen on rocky planets in visible light. UNDERGROUND (Ultra-fast AO techNology Determination for Exoplanet imageRs from the GROUND), a collaboration built in Feb. 2023 at the Optimal Exoplanet Imagers Lorentz Workshop, aims to (1) motivate oxygen detection in Proxima Centauri b and analogs as an informative science case for high-contrast imaging and direct spectroscopy, (2) overview the state of the field with respect to visible exoplanet imagers, and (3) set the instrumental requirements to achieve this goal and identify what key technologies require further development.

Optimal atmospheric conditions are beneficial for detecting exoplanets via High Contrast Imaging (HCI), as speckles from Adaptive Optics’ (AO’s) residuals can make it difficult to identify exoplanets. While AO systems greatly improve our image quality, having access to real-time estimates of atmospheric conditions could also help astronomers use their telescope time more efficiently in the search for exoplanets as well as aid in the data reduction process. The Shack-Hartmann Imaging Motion Monitor (SHIMM) is an atmospheric profiler that utilizes a Shack-Hartmann wavefront sensor to create spot images of a single star in order to reconstruct important atmospheric parameters such as the Fried parameter (r₀), C²_n profile and coherence time. Due to its simplicity, the SHIMM can be directly used on a telescope to get in situ measurements while observing. We present our implementation of the Nickel-SHIMM design for the one meter Nickel Telescope at Lick Observatory. We utilize an HCIPy simulation of turbulence propagating across a telescope aperture to verify the SHIMM data reduction pipeline as we begin on-sky testing. We also used on-sky data from the AO system on the Shane Telescope to further validate our analysis, finding that both our simulation and data reduction pipeline are consistent with previously determined results for the Fried parameter at the Lick Observatory. Finally, we present first light results from commissioning of the Nickel-SHIMM.

The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an under-construction thermal infrared high-contrast integral field spectrograph that will be located at the W. M. Keck Observatory. SCALES will detect and characterize planets that are currently inaccessible to detailed study by operating at thermal (2 μm to 5 μm) wavelengths and leveraging integral-field spectroscopy to readily distinguish exoplanet radiation from residual starlight. SCALES’ wavelength coverage and medium-spectral-resolution (R ∼ 4,000) modes will also enable investigations of planet accretion processes. We explore the scientific requirements of additional custom gratings and filters for incorporation into SCALES that will optimally probe tracers of accretion in forming planets. We use ray-traced hydrogen emission line profiles (i.e., Brγ, Brα) and the SCALES end-to-end simulator, scalessim, to generate grids of high-fidelity mock datasets of accreting planetary systems with varying characteristics (e.g., Teff, planet mass, planet radius, mass accretion rate). In this proceeding, we describe potential specialized modes that best differentiate accretion properties and geometries from the simulated observations.

Psisim is a software suite that acts as a high-level simulation tool for the development and characterization of instrument performance in stellar and substellar observations. Psisim is capable of modeling science yields, generating simulated spectra, and acting as an exposure time calculator. Its modular framework allows for implementation of various instruments, including imagers and spectrographs. Currently models exist for KPIC, MODHIS, GPI, HISPEC, PSI-Blue and PSI-Red. One of the larger functionalities of psisim is the simulation of exoplanet observations behind adaptive optics systems. Utilizing instrument characteristics, such as Strehl ratio, throughput, etc., and pulling from models generated on the fly or from various common atmospheric grids, psisim is able to return simulated spectra and separate noise components from sky, photon, and thermal sources. We are then able to evaluate instrument performance and perform simulated science programs. We have recently upgraded psisim with a module for observations in polarized light. Manipulation of instrumental Mueller matrices mimics the effect optical components have on incoming light. Inversion of the instrumental Mueller matrices enables recovery of desired Stokes parameters, along with associated observational noise. Here we will provide an overview of psisim, highlighting key features and its adaptability for use with new instruments. We’ll demonstrate how psisim simulates observation with an example, describe a few use cases where it has proved useful, and provide some preliminary results of spectro-polarimetric observations using the new polarimetry mode.

The Gemini Planet Imager (GPI), is a facility class instrument for the Gemini Observatory with the primary goal of directly detecting young Jovian planets. After spending 2013 - 2020 at Gemini South, the instrument is currently undergoing maintenance and upgrades before its transition to Gemini North as GPI 2.0. Among the upgrades are significant changes to the Integral Field Spectrograph (IFS), including the installation of new prisms, Lyot stops/apodizers, and filters. The upgrades are expected to improve overall performance in the relevant wavelengths and angular separations needed for GPI 2.0.

High-contrast imaging has been used to discover and characterize dozens of exoplanets to date. The primary limiting performance factor for these instruments is contrast, the ratio of exoplanet to host star brightness that an instrument can successfully resolve. Contrast is largely determined by wavefront error, consisting of uncorrected atmospheric turbulence and optical aberrations downstream of AO correction. Single-point diamond turning allows for high-precision optics to be manufactured for use in astronomical instrumentation, presenting a cheaper and more versatile alternative to conventional glass polishing. This work presents measurements of wavefront error for diamond-turned aluminum optics in the Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument, a 2 micron to 5 micron coronagraphic integral field spectrograph under construction for Keck Observatory. Wavefront error measurements for these optics are used to simulate SCALES’ point spread function using physical optics propagation software poppy, showing that SCALES’ contrast performance is not limited by wavefront error from internal instrument optics.

We present a generalized non-negative factorization (NMF)-based data reduction pipeline for circumstellar disk and exoplanet detection. By using an adaptable pre-processing routine that applies algorithmic masks and corrections to improper data, we are able to easily offload the computationally-intensive NMF algorithm to a Graphics Processing Unit (GPU), significantly increasing computational efficiency. NMF has been shown to better preserve disk structural features compared to other post-processing approaches and has demonstrated improvements in the analysis of archival data. The adaptive pre-processing routine of this pipeline, which automatically aligns and applies image corrections to the raw data, is shown to significantly improve chromatic halo suppression. Utilizing HST-STIS and JWST-MIRI coronagraphic datasets, we demonstrate a factor of five increase in real-time computational efficiency by using GPUs to perform NMF compared to using CPUs. Additionally, we demonstrate the usefulness of higher numbers of NMF components with SNR and contrast improvements, which necessitates the use of a more computationally efficient approach for data reduction.

The Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an Integral Field Spectrograph (IFS), under construction for W. M. Keck Observatory. It is optimized for 2 to 5-micron spectroscopy of exoplanets and also has a 1 to 5-micron imaging channel. As various optics arrive, we aim to validate their performances individually. In this paper, we present measurements and measurement techniques used to validate SCALES optics in the lab, including filter substrates, pupil masks for the cold stop and Lyot stops, neutral density filters, and diamond-turned mirrors.

SCALES (Slicer Combined with Array of Lenslets for Exoplanet Spectroscopy) is a 2 micron to 5 micron high-contrast lenslet-based Integral Field Spectrograph (IFS) designed to characterize exoplanets and their atmospheres. The SCALES medium-spectral-resolution mode uses a lenslet subarray with a 0.34 x 0.36 arcsecond field of view which allows for exoplanet characterization at increased spectral resolution. We explore the sensitivity limitations of this mode by simulating planet detections in the presence of realistic noise sources. We use the SCALES simulator scalessim to generate high-fidelity mock observations of planets that include speckle noise from their host stars, as well as other atmospheric and instrumental noise effects. We employ both angular and reference differential imaging as methods of disentangling speckle noise from the injected planet signals. These simulations allow us to assess the feasibility of speckle deconvolution for SCALES medium resolution data, and to test whether one approach outperforms another based on planet angular separations and contrasts.

The Slicer Combined with an Array of Lenslets for Exoplanet Spectroscopy (SCALES) instrument is a lenslet-based integral field spectrograph that will operate at 2 to 5 microns, imaging and characterizing colder (and thus older) planets than current high-contrast instruments. Its spatial resolution for distant science targets and/or close-in disks and companions could be improved via interferometric techniques such as sparse aperture masking. We introduce a nascent Python package, NRM-artist, that we use to design several SCALES masks to be non-redundant and to have uniform coverage in Fourier space. We generate high-fidelity mock SCALES data using the scalessim package for SCALES’ low spectral resolution modes across its 2 to 5 micron bandpass. We include realistic noise from astrophysical and instrument sources, including Keck adaptive optics and Poisson noise. We inject planet and disk signals into the mock datasets and subsequently recover them to test the performance of SCALES sparse aperture masking and to determine the sensitivity of various mask designs to different science signals.

The Astro2020 Decadal Survey calls for a mission yield goal of 25 or more habitable zone planets detection and characterization in its recommendation of next NASA flagship mission, the Habitable World Observatory (HWO). Multi-Star Wavefront Control (MSWC) is a technique that enables simultaneous star light suppression of a binary or more star system. It has the potential to help achieve the goal by substantially increasing viable target samples to beyond single star systems. Technology development for MSWC has been ongoing for a number of years. Recently a better than 1e-7 monochromatic contrast was demonstrated at JPL’s High Contrast Imaging Testbed (HCIT) with a true binary source having similar Alpha Centauri star system separation for the first time. Here we present (High Order) Wavefront Sensing and Control (HOWFSC) modeling analysis of the testbed experiments for improving future performance. Our model is a modified extension of the HOWFSC engineering model that has proven to be a valuable tool for Roman Coronagraph Instrument (CGI) and was validated on the HCIT. It includes crucial engineering features and factors relevant to testbed (while omitting CGI specific elements) such as probing and sensing with detector noise and finite bandwidth used. The analysis provides important insight into and understanding of MSWC testbed experiments and identifies key performance-limiting factors that were not previously considered. Adjustments in both hardware and WFSC strategy and algorithm are discussed for next round testbed experiments to improve performance necessary for both Roman and HWO.

NASA’s Nancy Grace Roman Space Telescope mission includes a Coronagraph Instrument (CGI) to demonstrate active Wavefront Sensing and Control (WFSC) for future direct imaging and characterization of exoplanets. CGI is in the instrument integration and testing phase and is scheduled to be delivered next year for integration into the Roman observatory. Key flight components, such as Deformable Mirrors (DMs) and detectors, have been recently characterized and integrated into the CGI optical system. A series of system level coronagraph requirement verifications in a vacuum chamber will take place starting later this year. Among them is the static raw contrast with a coronagraph stimulus source. This is the only time CGI will have the opportunity for dark hole digging before In-Orbit Commissioning (IOC). CGI High Order Wavefront Sensing and Control (HOWFSC) modeling has played an important role in assisting many engineering decisions and risk assessments and mitigations throughout the project phases, including when calibration data of key components and their imperfections became available. Here we present some of the latest modeling studies involving special use cases or properties of the DMs and detectors and give our current-best-estimates on static raw contrasts for the upcoming performance verification. Contrast performance for IOC phase WFSC with a typical reference star and its brightness is also provided. All evaluations are performed with the full features of HOWFSC modeling and extensive engineering details. This work is performed at the Jet Propulsion Laboratory / California Institute of Technology under contract to NASA.

High-contrast, direct imaging of exoplanets is a key objective for the future of astronomy. Underpinning both the development and successful deployment of future direct imaging missions is the ability to analyze the resulting data. Therefore, in order to inform noise budget requirements and fully leverage high-resolution direct images, it is critical to develop post-processing algorithms that are versatile, efficient, and reliable. This work leverages recent advancements in starshade simulation technology and presents a Convolutional Neural Network (CNN) for detecting exoplanet signals from direct images. The proposed architecture modifies U-Net, a semantic segmentation architecture, to directly regress the coordinate location of exoplanet signals from a synthetic star-shade imaging dataset. Results from a limited test set of 144 images indicate that the CNN achieves an average precision and recall of 0.925 ± 0.012 and 0.923 ± 0.018, respectively. Additionally, the CNN does not require processing the data through conventional background estimation algorithms prior to detection and performs inference on single images, showcasing the potential of supervised machine learning as a versatile approach for exoplanet detection.

Coronagraphs are bandwidth limited. BLOCT takes the approach of "divide and conquer" with a front end that is dispersive. Wavelengths are addressed in exquisitely narrow bands using a process of double dispersion. First the wavefront is broken into a spectrum and then it is collimated. A matched pair of wavefronts that have been split form the basis of a long baseline interferometer. Notably this telescope draws from the entire history of astronomical optics. The initial afocal mirror telescope is a Mersenne (1636). The double dispersion traces its roots to Newton's Dual Prism Experiment (1666). The division of light into its spectrum by diffraction was first demonstrated by Rittenhouse (1785). The division of star light into wavelengths derives from von Fraunhofer (1819). The ruled plane grating was developed by Rowland (1880). The interferometric beam splitter and resulting beat pattern was developed by Michelson who measured the diameter of Betelgeuse on the Wilson telescope (1920).

Accurate high-contrast imaging is achieved using Deformable Mirrors (DM) with actuator precision of 10s pi-cometers. Beyond the demanding wavefront control requirements needed to achieve a contrast ratio of 10⁻¹⁰, there is an additional science driver for achieving this ratio over an Outer Working Angle (OWA) large enough to image an exoplanet in a 1 AU orbit around a star 10 parsec or 0.1′′ maximum separation from its host star. Using the formula OWA = Naλ/2D dictates that as D increases, the primary mirror diameter, so does the total number of actuator elements (Na² ). Then, the demands of cabling, power, and mass also increase as Na², which is difficult to achieve for DM-based space missions. Furthermore, fixed-position actuators require high reliability. Our technology has the potential of being able to reduce the number of wires from Na² to 2Na and with a motion stage can mitigate the dead pixel issue. We report here our work to mature our technology which is based on magnetostriction and magnetization of a magnetic hard overcoat to enable maintaining in-plane stress and set-and-forget DM surface changes when actuators are powered off.

The Habitable Worlds Observatory mission will require coronagraphs capable of achieving contrasts of 1e-10 to detect exo-Earths. The choice of coronagraph depends on finding a solution that is achromatic within a 20% bandwidth, insensitive to low order aberrations and polarization independent. We present two scalar vortex phase mask designs which employ a Roddier phase dimple and a dual zone phase dimple to improve the achromatic performance by addressing the chromatic stellar leakage not handled by the vortex. We show that using these dimples, it is possible to substantially improve the broadband contrast performance of existing scalar vortex phase masks.

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 × 10⁻⁸ between 3-18 λ/D at the IACT, and 6 × 10⁻⁸ between 3-14 λ/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.

Connecting a coronagraph instrument to a spectrograph via a single-mode optical fiber is a promising technique for characterizing the atmospheres of exoplanets with ground and space-based telescopes. However, due to the small separation and extreme flux ratio between planets and their host stars, instrument sensitivity will be limited by residual starlight leaking into the fiber. To minimize stellar leakage, we must control the electric field at the fiber input. Implicit Electric fFeld Conjugation (iEFC) is a model-independent wavefront control technique in contrast with classical Electric Field Conjugation (EFC) which requires a detailed optical model of the system. We present here the concept of an iEFC-based wavefront control algorithm to improve stellar rejection through a single-mode fiber. As opposed to image-based iEFC which relies on minimizing intensity in a dark hole region, our approach aims to minimize the amount of residual starlight coupling into a single-mode fiber. We present broadband simulation results demonstrating a normalized intensity ≥ 10⁻¹⁰ for both fiber-based EFC and iEFC. We find that both control algorithms exhibit similar performance for the low wavefront error case, however, iEFC outperforms EFC by ≈ 100x in the high wavefront error regime. Having no need for an optical model, this fiber-based approach is theoretically easier to implement than conventional EFC on future ground and space-based telescope missions.

Future large space telescope missions for directly imaging exoplanets with internal coronagraphs will require picometer level low-order wavefront control to reach the 1e-10 starlight suppression required to detect terrestrial exoplanets. This paper aims to characterize the reflective Lyot-stop Low-Order Wavefront Sensor (LLOWFS) for the application where a transmissive focal plane mask is used, such as the Vector Vortex Coronagraph (VVC). This paper first defines the control requirements for such a mission based on the low-order tolerance of the VVC. The LLOWFS performance is then derived through optical simulation and compared to the requirements. The performance is calculated as a function of the target star brightness and aperture size and the final closed-loop stability is simulated using varying models for telescope pointing jitter and wavefront drift.

Coronagraphy is one of the leading technologies for directly imaging exoplanets. To suppress starlight at high contrast, coronagraphic masks must be aligned with extreme accuracy and precision, and model-based wavefront correction algorithms must be given accurate calibration parameters. Manual alignment and calibration of coronagraphic masks is typical in most testbeds, but automation is necessary to guarantee accuracy and repeatability. To meet the strict requirements of NASA’s Nancy Grace Roman Space Telescope Coronagraph Instrument, the Jet Propulsion Laboratory created a unit-tested software package for coronagraphic alignment and calibration. For public release, we made the software more user friendly and added more routines from the High Contrast Imaging Testbed (HCIT) facility. This open-source software package, named Coralign, contains a suite of algorithms for the alignment and calibration of the unmasked beam, deformable mirrors, and several types of coronagraphic masks (e.g., an occulter, vortex, Lyot stop, apodizer, and field stop). Coralign is available in Python (and soon in MATLAB) at github.com/nasa-jpl/coralign.

NASA is about to embark on an ambitious program to develop a Habitable Worlds Observatory (HWO) flagship mission to directly image approximately 25 potentially Earth-like planets and spectroscopically characterize them for signs of life, as recommended by the Astro2020 decadal survey. In addition, Astro2020 recommended a new approach for flagship formulation, which involves increasing the scope and depth of early, pre-phase A trades and technology maturation, as part of the new Great Observatories Maturation Program (GOMAP). The critical capability of the HWO mission is starlight suppression. To inform future architecture trades, it is necessary to survey a wide range of technologies, from the relatively mature ones such as the ones described in the LUVOIR and HabEx reports, to the relatively new and emerging ones, which may lead to breakthrough performance. In this paper, we present an interim update on a new effort, initiated by NASA’s Exoplanet Exploration Program (ExEP), to survey coronagraph design options for HWO. We present a preliminary summary of the survey, including: (1) a current list of coronagraph design options; (2) proposed evaluation criteria, such as expected mission yields and feasibility of maturing to TRL5 by 2029; and (3) tools and methods which we are using to quantify evaluations of different designs. While not charged to down-select or prioritize the different coronagraph designs, this survey is expected to be valuable in informing future mission teams of coronagraph design options. All interested coronagraph researchers are welcome to participate in this survey by contacting the first two authors of this paper.

The High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed is a segmented aperture coronagraph simulator designed to be a systems level prototype demonstration for the proposed Habitable Worlds Observatory recommended by the 2020 Astronomical Decadal Survey. An important technical component of operating HiCAT is a method of measuring the Wavefront Error (WFE) on the testbed. Here we present our implementation of the differential Optical Transfer Function (dOTF) phase retrieval technique on HiCAT and the WFE calibration experiments we have developed using the technique. We use dOTF to improve the wavefront calibration map of one of HiCAT’s Deformable Mirrors (DMs) as well as to measure low-order Non-Common Path Aberrations (NCPA) between the focal and imaging planes of the coronagraph.

Uncorrected wavefront errors create speckle noise in high-contrast observations at small inner-working angles. These speckles can be sensed and controlled by using coronagraph integrated wavefront sensors. Here, we will present how the Phase Induced Amplitude Apodized Complex Mask Corongraph (PIAACMC) can be integrated with both a Self-Coherent Camera (SCC) for focal plane wavefront sensing and an extremely sensitivity high-order pupil plane Zernike Wavefront Sensor (ZWFS). Non-common path aberrations can be completely erased by integrating both sensors into the PIAACMC, which is of extremely high importance in high-contrast imaging.

Diffractive Interfero Coronagraph Exoplanet Resolver (DICER) is a notional infrared space observatory that would detect all habitable exoplanets within 10 pc of the Sun and determine whether there is ozone in their atmospheres. We are aiming at an approximate $1B target cost for a several year mission, and an observatory that easily fits in a Falcon heavy launch vehicle. Light (near 10 microns) is collected with two flat diffraction gratings that are each 10 meters long. Each grating feeds light into smaller focusing secondary optics that are 1 meter across. An achromatic interferometer (Dispersion Leverage Coronagraph, DLC) reduces the light from the host star by a factor of at least 10⁵. A second high resolution spectrograph separates exoplanet light from the background. The one-dimensional diffraction limit of this system (0.1") is sufficient to resolve an Earth-like planet orbiting a Sun-like star at a distance of 10 pc. The gratings can be tilted to scan through a small range of wavelengths around 10 microns so that the ozone absorption line can be detected.

We report on the Dispersion Leverage Coronagraph (DLC), a variation of the Achromatic Interfero Coronagraph (AIC) that is designed for optical systems featuring dispersive primary objectives that provide enhanced one-dimensional angular resolution. It was specifically designed for the Diffractive Interfero Coronagraph Exoplanet Resolver (DICER), a notional 20m class infrared space telescope utilizing the enhanced one-dimensional angular resolution of large diffraction gratings in order to discover and characterize near-Earth exoplanets. Here we develop the theoretical foundation for DLC, the interferometric system utilized by the DICER instrument for reduction of the exoplanet/host-star flux ratio. While the core method of operation of DLC remains very similar to AIC, the introduction of dispersive primaries alters the optical system in many nontrivial aspects. Here we derive important properties of the DLC system including focal plane transmission maps, stellar leakage, residual optical path difference tolerance, and pointing error/jitter considerations. Ultimately, we found that DLC effectively nulls a target spectrum across the entire focal plane, allows for 2D/λ diffraction limited imaging, and requires asymmetrical fine-guidance tolerances on pointing error/jitter.

Since the first confirmed discovery of exoplanets in 1992, multiple observational methods have been developed. Most methods of their discovery use the influence of a planet on its host star. These methods lose sensitivity when a planet is distant from its star and has a long orbital period. This article proposes a method inspired by Hanbury-Brown Twiss (HBT) interferometry, to find exoplanets which exercise a very small influence on their host star. Our method relies on an extremely high sensitivity of the phase correlations to an asymmetry of the luminous system.

Starshades have deeper contrast, wider bandwidth, higher throughput, and smaller working angle than coronagraphs and may someday become the method of choice for direct observation of extrasolar planets. A starshade is a flower-shaped spacecraft structure, which is positioned between an exoplanet’s host star and a space telescope. The starshade casts a shadow on the telescope enabling viewing of a faint exoplanet without being overwhelmed by the glare from the parent star. However, to view faint exoplanets, antireflection coatings must be added to the starshade’s razor edges, as well as its light-blocking membranes. We have demonstrated antireflection coatings, which utilize resonating nanoscale cavities to absorb straylight by approximately an order-of-magnitude compared to uncoated surfaces. The optical performance of our coatings applied to the starshade edges is discussed in a separate paper [McKeithen, et al. Ref. 1]. Herein, we discuss the optical performance of light-absorbing coatings applied to broad-area, flexible, polyimide membranes. The coatings are manufactured using a novel, roll-to-roll, vacuum coating process.

The PRime-focus Infrared Microlensing Experiment (PRIME) camera is part of the joint NASA-JAXA project in support of the spaceflight Roman Space Telescope project development. It is designed to accommodate the needs of the large-scale survey of the microlensing events in the Galactic bulge. The camera is placed in the prime focus of the 1.8-m telescope dedicated to this project. With four large-format infrared detectors, the instrument covers a field of view about 1.3 square degrees. Over the few years preceding and during the operations of the Roman Space Telescope, the instrument will be used for continuous monitoring of selected fields in the Galactic bulge for microlensing events and a number of other science programs of the consortium.

This PDF file contains the front matter associated with SPIE Proceedings Volume 12680, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.