This PDF file contains the front matter associated with SPIE Proceedings Volume 11823, including the Title Page, Copyright Information, and Table of Contents.

The Keck Planet Imager and Characterizer (KPIC) is a novel instrument that combines high-contrast imaging with high-resolution spectroscopy to enable high-dispersion coronagraphy (HDC) techniques that allow us to characterize directly imaged exoplanets at a spectral resolution of R~35,000. At this resolution, individual absorption lines in planetary atmospheres are spectrally resolved, allowing for measurements of molecular abundances to constrain chemical composition, planetary radial velocities to constrain orbital configurations, and planetary spin to constrain angular momentum evolution. I will provide an overview of the instrument, with a focus on its novel fiber injection unit (FIU) and the use of single mode fibers. I will discuss new HDC techniques we are developing that take advantage of the single-mode fibers of KPIC to both spatially and spectrally filter out the bright glare of the host stars to study the faint exoplanets. In particular, we have demonstrated the ability to forward model the high-resolution spectrum of diffracted stellar speckles, allowing us to directly fit our data without the need for cross-correlation functions. I will present some early science observations from KPIC that successfully demonstrate its technical capabilities, with the highlight being the first detection of all four HR 8799 planets at high spectral resolution. I will conclude with future avenues to push the sensitivity of HDC techniques and discuss possible synergies with other exoplanet characterization techniques such as long-baseline interferometry.

To directly detect exoplanets and protoplanetary disks, the development of high accuracy wavefront sensing and control (WFS&C) technologies is essential, especially for ground-based Extremely Large Telescopes (ELTs). The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is a high-contrast imaging platform to discover and characterize exoplanets and protoplanetary disks. It also serves as a testbed to validate and deploy new concepts or algorithms for high-contrast imaging approaches for ELTs, using the latest hardware and software technologies on an 8-meter class telescope. SCExAO is a multi-band instrument, using light from 600 to 2500 nm, and delivering a high Strehl ratio (>80% in median seeing in H-band) downstream of a low-order correction provided by the facility AO188. Science observations are performed with coronagraphs, an integral field spectrograph, or single aperture interferometers. The SCExAO project continuously reaches out to the community for development and upgrades. Existing operating testbeds such as the SCExAO are also unique opportunities to test and deploy the new technologies for future ELTs. We present and show a live demonstration of the SCExAO capabilities (Real-time predictive AO control, Focal plane WFS&C, etc) as a host testbed for the remote collaborators to test and deploy the new WFS&C concepts or algorithms. We also present several high-contrast imaging technologies that are under development or that have already been demonstrated on-sky.

We present first results from a new exoplanet direct imaging survey being carried out with the Subaru Coronagraphic Extreme Adaptive Optics project coupled with the CHARIS integral field spectrograph. Our survey targeting stars showing evidence for a statistically significant astrometric acceleration from the Hipparcos and Gaia satellites implying the existence of substellar or planetary companions at sub-arcsecond separations.. JHK low-resolution spectra from CHARIS constrain newly-discovered companion spectral types, temperatures, and gravities. Relative astrometry of companions from SCExAO/CHARIS and absolute astrometry of the star from Hipparcos and Gaia together yield direct dynamical mass constraints, circumventing usual challenges in inferring the masses of imaged planets from luminosity evolution models. Even in its infancy, our survey has already yielded multiple discoveries, including at least one likely jovian planet at a moderate orbital separation and multiple other substellar companions. We describe how our small nascent survey is yielding a far higher detection rate than large blind surveys from GPI and SPHERE and the path forward for imaging and characterizing planets at lower masses and smaller orbital separations than previously possible.

MagAO-X system is a new adaptive optics for the Magellan Clay 6.5m telescope. MagAO-X has been designed to provide extreme adaptive optics (ExAO) performance in the visible. VIS-X is an integral-field spectrograph specifically designed for MagAO-X, and it will cover the optical spectral range (450 – 900 nm) at high-spectral (R=15.000) and high-spatial resolution (7 mas spaxels) over a 0.525 arsecond field of view. VIS-X will be used to observe accreting protoplanets such as PDS70 b & c. End-to-end simulations show that the combination of MagAO-X with VIS-X is 100 times more sensitive to accreting protoplanets than any other instrument to date. VIS-X can resolve the planetary accretion lines, and therefore constrain the accretion process. The instrument is scheduled to have its first light in Fall 2021. We will show the lab measurements to characterize the spectrograph and its post-processing performance.

We present an on-sky demonstration of a post-processing technique for companion detection called Stochastic Speckle Discrimination (SSD) and its ability to improve the detection of faint companions using SCExAO and the MKID Exoplanet Camera (MEC). Using this SSD technique, MEC is able to resolve companions at a comparable signal to noise to other integral field spectrographs solely utilizing photon arrival time information and without the use of any PSF subtraction techniques. SSD takes advantage of photon counting detectors, like the MKID detector found in MEC, to directly probe the photon arrival time statistics that describe the speckle field and allows us to identify and distinguish problematic speckles from companions of comparable brightness in an image. This technique is especially effective at close angular separations where the speckle intensity is large and where traditional post-processing techniques, like ADI, suffer.

The advantage of having a high-fidelity instrument simulation tool developed in tandem with novel instrumentation is having the ability to investigate, in isolation and in combination, the wide parameter space set by the instrument design. SCALES, the third generation thermal-infrared diffraction limited imager and low/med-resolution integral field spectrograph being designed for Keck, is an instrument unique in design in order to optimize for its driving science case of direct detection and characterization of thermal emission from cold exoplanets. This warranted an end-to-end simulation tool that systematically produces realistic mock data from SCALES to probe the recovery of injected signals under changes in instrument design parameters. In this paper, we quantify optomechanical tolerance and detector electronic requirements set by the fiducial science cases, and test the consequences of update to the design of the instrument on meeting these requirements.

The Planetary Systems Imager (PSI) is a proposed instrument for the Thirty Meter Telescope (TMT) that provides an extreme adaptive optics (AO) correction to a multi-wavelength instrument suite optimized for high contrast science. PSI's broad range of capabilities, spanning imaging, polarimetry, integral field spectroscopy, and high resolution spectroscopy from 0.6–5 μm, with a potential channel at 10 μm, will enable breakthrough science in the areas of exoplanet formation and evolution. Here, we present a preliminary optical design and performance analysis of the 2–5 μm component of the PSI AO system, which must deliver the wavefront quality necessary to support infrared high contrast science cases.

As the number of confirmed exoplanets continues to grow, there is an increased push to spectrally characterize them to determine their atmospheric composition, formation paths, rotation rates, habitability, and much more. However, there is a large population of known exoplanets that either do not transit their star or have been detected at very small angular separations such that they are inaccessible to traditional coronagraph systems. Vortex Fiber Nulling (VFN) is a new single-aperture interferometric technique that uses the entire telescope pupil to bridge the gap between RV methods and traditional coronagraphy by enabling the direct observation and spectral characterization of targets at and within the diffraction limit. By combining a vortex mask with a single mode fiber, the on-axis starlight is rejected while the off-axis planet light is coupled and efficiently routed to a radiometer or spectrograph for analysis. We have demonstrated VFN in the lab monochromatically in the past. In this talk we present a polychromatic validation of VFN with null depths of 1e-4 across 10% bandwidth light. We also provide an update on deployment plans and predicted yield estimates for the VFN mode of the Keck Planet Imager and Characterizer (KPIC) instrument. Using PSISIM, a simulation package developed by our group, we asses KPIC VFN's ability to detect and characterize different types of targets including known exoplanets detected via the RV method. The KPIC VFN on-sky demonstration will pave the road to deployment on future instruments like HISPEC and MODHIS where it could provide high-resolution spectra of sub-Jupiter mass planets down to 5 milliarcseconds from their star.

The coupling of large telescopes to astronomical instruments has historically been challenging due to the tension between instrument throughput and stability. Light from the telescope can either be injected wholesale into the instrument, maintaining high throughput at the cost of point-spread function (PSF) stability, or the time-varying components of the light can be filtered out with single-mode fibers (SMFs), maintaining instrument stability at the cost of light loss. Today, the field of astrophotonics provides a potential resolution to the throughput- stability tension in the form of the photonic lantern (PL): a tapered waveguide which can couple a time-varying and aberrated PSF into multiple diffraction-limited beams at an efficiency that greatly surpasses direct SMF injection. As a result, lantern-fed instruments retain the stability of SMF-fed instruments while increasing their throughput. To this end, we present a series of numerical simulations characterizing PL performance as a function of lantern geometry, wavelength, and wavefront error (WFE), aimed at guiding the design of future diffraction-limited spectrometers. These characterizations include a first look at the interaction between PLs and phase-induced amplitude apodization (PIAA) optics. We find that Gaussian-mapping beam-shaping optics can enhance coupling into 3-port lanterns but offer diminishing gains with larger lanterns. In the y- and J - band (0.97–1.35 µm) region, with moderately high WFE (∼ 10% Strehl ratio), a 3-port lantern in conjunction with beam-shaping optics strikes a good balance between pixel count and throughput gains. If pixels are not a constraint, and the flux in each port will be dominated by photon noise, then larger port count lanterns will provide further coupling gains due to a greater resilience to tip-tilt errors. Finally, we show that lanterns can maintain high operating efficiencies over large wavelength bands where the number of guided modes at the lantern entrance drops, if care is taken to minimize the attenuation of weakly radiative input modes.

Post Extreme Adaptive-Optics (ExAO) spectro-interferometers design allows high contrast imaging with an inner working angle down to half the theoretical angular resolution of the telescope. This regime, out of reach for conventional ExAO imaging systems, is obtained thanks to the interferometric recombination of multiple sub-apertures of a single telescope, using single mode waveguides to remove speckle noise. The SCExAO platform at the Subaru telescope hosts two instruments with such design, coupled with a spectrograph. The FIRST instrument operates in the Visible (600-800nm, R~400) and is based on pupil remapping using single-mode fibers. The GLINT instrument works in the NIR (1450-1650nm, R~160) and is based on nulling interferometry. We present here how these photonic instruments have the unique capability to simultaneously do high contrast imaging and be included in the wavefront sensing architecture of SCExAO.

We describe a new high-contrast imaging capability well suited for studying planet-forming disks: near-infrared (NIR) high-contrast spectropolarimetric imaging with the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with the CHARIS integral field spectrograph (IFS). The advent of extreme AO systems, like SCExAO, has enabled recovery of planet-mass companions at the expected locations of gas-giant formation in young disks alongside disk structures (such as gaps or spirals) that may indicate protoplanet formation. In combination with SCExAO, the CHARIS IFS in polarimetry mode allows characterization of these systems at wavelengths spanning the NIR J, H, and K bands (1.1–2.4 μm, R~20) and at angular separations as small as 0.04”.

We present the design and lab performance of a prototype lenslet-slicer hybrid integral field spectrograph (IFS), validating the concept for use in future instruments like SCALES/PSI-Red. By imaging extrasolar planets with IFS, it is possible to measure their chemical compositions, temperatures and masses. Many exoplanet-focused instruments use a lenslet IFS to make datacubes with spatial and spectral information used to extract spectral information of imaged exoplanets. Lenslet IFS architecture results in very short spectra and thus low spectral resolution. Slicer IFSs can obtain higher spectral resolution but at the cost of increased optical aberrations that propagate through the down-stream spectrograph and degrade the spatial information we can extract. We have designed a lenslet/slicer hybrid that combines the minimal aberrations of the lenslet IFS with the high spectral resolution of the slicer IFS. The slicer output f/# matches the lenslet f/# requiring only additional gratings.

A key aspect of the search for earth-like exoplanets with direct imaging, is determining if the exoplanet is in the habitable zone. For mission design of potential future direct imaging missions, such as HabEx and LUVOIR, an efficient cadence of observations is needed. Previous work has shown that three epochs, spanning more than half a period, is the minimum to determine orbital parameters to 10%. One aspect that still needs improvement is the ability to fit multiple planets with limited prior information about which planet is which. Since data from direct observations is expected to consist of multiple objects at each epoch, looking at each epoch separately is not sufficient to decide whether 1) a detected object is part of an exosolar system and 2) which planet it corresponds to. Existing multi-planet trajectory matching libraries, such as “Orbits For The Impatient” (OFTI), currently require the user to specify which data points belong to which planet. This assumes that the user has already matched true-positive detections to planets. Additionally, this planet matching between detected objects needs to be taken into account when assessing the impact of observation scheduling on the accuracy of trajectory estimation. To address this need for fitting orbits to multiple objects with limited knowledge, we propose an approach that uses a Monte Carlo study of different observation schedules and planetary systems. For each case we automatically match observations to planets and check the accuracy of the match. By considering a large number of such cases, we provide constraints on the number of observations and their spacing necessary to “deconfuse” the detections. We present preliminary planet matching success rates for several observation schedules based on simulated planetary systems and assess the accuracy of trajectory fitting combined with OFTI.

Giant exoplanets on 10-100 au orbits have been directly imaged around young stars. The peak of the thermal emission from these warm young planets is in the near-infrared (∼1-5 µm), whereas mature, temperate exoplanets (i.e., those within their stars’ habitable zones) radiate primarily in the mid-infrared (mid-IR: ∼10 µm). If the background noise in the mid-IR can be mitigated, then exoplanets with low masses–including rocky exoplanets–can potentially be imaged in very deep exposures. Here, we review the recent results of the Breakthrough Watch/New Earths in the Alpha Centauri Region (NEAR) program on the Very Large Telescope (VLT) in Chile. NEAR pioneered a ground-based mid-IR observing approach designed to push the capabilities for exoplanet imaging with a specific focus on the closest stellar system, α Centauri. NEAR combined several new optical technologies–including a mid-IR optimized coronagraph, adaptive optics system, and rapid chopping strategy to mitigate noise from the central star and thermal background within the habitable zone. We focus on the lessons of the VLT/NEAR campaign to improve future instrumentation specifically on strategies to improve noise mitigation through chopping. We also present the design and commissioning of the Large Binocular Telescope’s Exploratory Survey for Super-Earths Orbiting Nearby Stars (LESSONS), an experiment in the Northern hemisphere that is building on what was learned from NEAR to further push the sensitivity of mid-IR imaging. Finally, we briefly discuss some of the possibilities that mid-IR imaging will enable for exoplanet science.

The James Webb Space Telescope (JWST) and its suite of instruments will offer significant capabilities towards the high contrast imaging of objects such as exoplanets, protoplanetary disks, and debris disks at short angular separations from their considerably brighter host stars. For the JWST user community to simulate and predict these capabilities for a given science case, the JWST Exposure Time Calculator (ETC) is the most readily available and widely used simulation tool. However, the ETC is not capable of simulating a range of observational features that can significantly impact the performance of JWST's high contrast imaging modes (e.g. target acquisition offsets, temporal wavefront drifts, small grid dithers, and telescope rolls) and therefore does not produce realistic contrast curves. Despite the development of a range of more advanced software that includes some or all of these features, these instead lack in either a) instrument diversity, or b) accessibility for novice users.

HgCdTe detectors with longer wavelength cutoffs were created for extending the lifetime of space-based applications because of their higher operating temperatures compared to arsenic doped silicon (Si:As) detectors. In addition to lower dark currents, the HgCdTe detectors also have higher quantum efficiencies compared to Si:As detectors. We are testing a HgCdTe detector with a 12.8 micron cutoff presented in Cabrera et al 2019 using HAWAII electronics in fast read-out mode to understand this array’s viability in instruments behind future ELT s that will directly image Earth-like planets. An f/100 system is required to operate the detector on a thirty meter diameter telescope without saturating, therefore we are the same f# system on the modified cryostat used to test and characterize the detector. We will present initial results on the detector’s quantum efficiency from 2 to 12 microns, read noise, dark current, and ability to tolerate flux levels that would be seen on future ELTs.

The majority of the 4,000 known exoplanets have been detected via transit photometry. Unambiguous characterization of their atmospheres for biosignatures such as H₂O, CH₄, O₃ and O₂ can be unlocked with high-resolution spectroscopy from space. To this end, we investigate the feasibility of a high-resolution (R=50,000) spectrograph on a CubeSat. This work compares optical design elements of traditional Echelle grating and a virtually imaged phased array (VIPA) using exposure time calculations. The limited magnitude when varying the spectral resolution and instrument size is reported. VIPAs on a 6U CubeSat is a cost-effective solution for high-resolution spectroscopy from space.

Coronagraph instruments rely on predictable and stable deformable mirror (DM) surface displacement to achieve the contrast required to detect Earth-sized exoplanets in the habitable zone of their host star. Anomalous DM behavior, such as unstable or pinned actuators, can limit contrast in coronagraphs. Simulating how these undesired behaviors affect the performance of a high contrast imaging architecture is important for developing requirements on their associated hardware. Simulating a vortex coronagraph (VC) with two deformable mirrors, this study quantifies how the number of pinned actuators affects the performance of Focal Plane Wavefront Sensing and Control algorithms using both Grid Search Electric Field Conjugation (EFC) and Planned EFC, which uses Beta-Bumping. The simulations also quantify how various types of voltage noise such as zero-mean Gaussian noise, zero-mean periodic noise, and drift can affect the contrast of a VC during an observation run. A tolerance of a change in the Mean Normalized Intensity of 1 × 10⁻¹¹ is allocated to both types of error. If Planned EFC is used, only 1 pinned actuator on both DMs can be tolerated. If only pure Grid Search EFC is used the DMs cannot have any pinned actuators. For the case of zero-mean Gaussian noise and zero-mean periodic noise, one can tolerate a noise standard deviation of no more than σ = 0.45 mV. For drift, one can only tolerate σ = 0.30 mV or less. These results show that the DM electronics and the DMs themselves need to be nearly defect free to avoid having more than 1 pinned actuator. It is important that the electronics designer attempts to minimize the noise by not only selecting high quality components but also control the output voltage to minimize drift.

Coronagraph instruments on future space telescopes will rely on deformable mirrors to create high contrast images for the direct detection of exoplanets. As part of the NASA Exoplanet Explorations Program’s coronagraph technology development efforts, two sets of Micro-Electro-Mechanical Systems (MEMS) deformable mirrors manufactured by Boston Micromachines Corporation were exposed to vibration and thermal cycles representative of launch conditions. The first set of mirrors were 952-actuator Kilo-DMs that successfully demonstrated 100% actuator survival and achieved ~1e- 8 contrast after the environmental test. The second round used an engineering-grade 2048-actuator deformable mirror on which few changes were identified after the environmental test. However, each actuator that changed behavior was flagged as anomalous beforehand or was directly adjacent to a defective actuator. From this result, we hypothesized that typical actuators on a science grade deformable mirror are robust to environmental testing. A third set of 2048-actuator deformable mirrors have been procured for a planned test to characterize the deformable mirrors using interferometric measurements, contrast results on a new in-air coronagraph testbed, and infrared microscopy on the internal structure of the MEMS devices.

The phase-induced amplitude apodization complex mask coronagraph (PIAACMC) provides high throughput and small inner working angle with little loss in image quality. Coronagraph compatibility with segmented apertures is essential for the success of habitable planet characterization with future large aperture space telescopes, such as the Large UV/Optical/Infrared (LUVOIR) and HabEx telescope mission concepts. The PIAACMC designs are compatible with such segmented telescope apertures with little loss of performance. We report the contrast and other performance results of a PIAACMC coronagraph with a LUVOIR-like pupil mask assembled and tested in a vacuum chamber at the JPL high contrast imaging testbed (HCIT). As the success of electric field conjugation (EFC) to achieve best contrast on the testbed is dependent upon a diffraction model of the coronagraph, we will also discuss variations of the testbed and its diffraction model with the PIAACMC design, including suspected sources of knowledge error in the EFC diffraction model.

Characterizing the atmospheres of Earth-sized planets necessitates of the advancement in broadband wavefront control for coronagraph systems in large segmented telescopes. At the the High-Contrast Spectroscopy Testbed (HCST) in the Exoplanet Technology Laboratory (ET Lab) at Caltech we are working on a new concept that utilizes single mode fibers (SMFs) at the image plane of the coronagraph to recover the light from the planet and feed it into a spectrograph. This technology has shown to be advantageous in both chromatic and wavefront control performance. Here we report on the status of our 20% bandwidth wavefront control experiments, in which we control the starlight coupling into an SMF in the image plane. We achieve levels of 10^-8 with deformable mirror (DM) solutions that hold the null through the SMF for several hours.

For direct imaging of exoplanets, Scalar Vortex Coronagraphs (SVCs) are an attractive alternative to the popularly used Vector Vortex Coronagraphs (VVCs). This is primarily because they are able to induce the same phase ramp regardless of the incoming light's polarization state without compromising throughput while maintaining small inner working angle. We tested a set of stepped SVC staircase masks in the Exoplanet Technology Laboratory (ET Lab) at Caltech on the High-Contrast Spectroscopy Testbed (HCST). Here we present some preliminary findings of their starlight suppression ability, achieving raw contrasts on the order of 10^-5 for 7 to 9 λ/D. We also characterized their chromatic performance and performed wavefront control to achieve preliminary contrasts on the order of 10^-7 with EFC for 6 to 10 λ/D. These initial experimental results with SVCs have shown scalar vortex technology has a great potential for future exoplanet direct imaging missions.

The Phase-Induced Amplitude Apodization Complex Mask Coronagraph (PIAACMC) is a coronagraph architecture for the next generation of large space telescopes optimized for habitable exoplanet imaging that can achieve attractive theoretical performance with high throughput at small inner working angles (IWA). PIAACMC designs are compatible with large, on-axis, segmented apertures such as the Large UV / Optical/ Infrared A (LUVOIRA) concept currently being considered by the decadal survey review which would greatly enhance the possibility to achieve statistically significant scientific yields and signal quality for direct imaging exoplanet surveys. A PIAACMC design has been recently created for LUVOIR-A and is currently being tested in vacuum at JPL’s High-Contrast Imaging Testbed (HCIT). In this work, we review the theoretical performance of the PIAACMC instrument designed to meet a 1e-9 raw contrast goal in 10% broadband light in a region from 2-8 λ/D both before and after the wavefront control loop. We use empirical measurements from the vacuum testbed to verify the instrument model and its performance including line-of-sight errors, instrument alignment, and fabricated components. In particular, the model verification includes measured sags of the manufactured PIAA mirrors by NuTek. The CMC mask was manufactured at JPL’s Microdevices Laboratory and we include surface profile characterization measurement. We assess the impact on performance of the different manufacturing and alignment errors.

Deformable mirrors (DMs) are an essential part of any coronagraphic, high contrast instrument. They mitigate optical aberrations in the system and can even be used to generate contrast for the coronagraph. MEMS DMs from Boston Micromachines have been selected as the baseline for two flagship space telescopes proposed to the 2020 Decadal Survey. Although MEMS DMs have over a decade of heritage on ground-based telescopes and in in-air testbeds around the globe, they have not been tested in vacuum down to the ∼10⁻¹⁰ contrast level needed to image terrestrial exoplanets. In this paper, we describe vacuum tests of MEMS DMs in the Decadal Survey Testbed at the Jet Propulsion Laboratory. The first challenge was a bright, temporally incoherent signal, which was identified as electronics noise and removed with a low-pass filter. After that, the contrast has been limited in broadband light by the strong print-through on the DM surfaces. We performed numerical simulations to confirm that conclusion and to characterize the improvements needed to the MEMS DM surfaces and the testbed layout to attain our goal of 10⁻¹⁰ contrast. Keywords: deformable mirror, coronagraph

We present recent laboratory results demonstrating high-contrast coronagraphy for future space-based large segmented telescopes such as the Large UV, Optical, IR telescope (LUVOIR) mission concept studied by NASA. The High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed aims to implement a system-level hardware demonstration for segmented aperture coronagraphs with wavefront control. The telescope hardware simulator employs a segmented deformable mirror with 36 hexagonal segments that can be controlled in piston, tip, and tilt. In addition, two continuous deformable mirrors are used for high-order wavefront sensing and control. The low-order sensing subsystem includes a dedicated tip-tilt stage, a coronagraphic target acquisition camera, and a Zernike wavefront sensor that is used to measure low-order aberration drifts.  We explore the performance of a segmented aperture coronagraph both in “static” operations (limited by natural drifts and instabilities) and in “dynamic” operations (in the presence of artificial wavefront drifts added to the deformable mirrors),  and discuss the estimation and control strategies used to reach and maintain the dark zone contrast. We summarize experimental results that quantify the performance of the testbed in terms of contrast, inner/outer working angle and bandpass, and analyze limiting factors by comparing against our end-to-end models.

The phase-apodized-pupil Lyot coronagraph (PAPLC) is a pairing of the apodized-pupil Lyot coronagraph (APLC) and the apodizing phase plate (APP) coronagraph that yields (in numerical simulations) inner working angles as close as 1.4 lambda/D at contrasts of 10^-10 and post-coronagraphic throughput of <75% for telescope pupils with central obscurations of up to 30%. PAPLC designs with a phase-only apodizer are entirely achromatic. Here we show that a single deformable mirror (DM) can serve as the phase apodizer in monochromatic light. We present the first laboratory demonstration of the PAPLC on a segmented telescope pupil, created by an IrisAO segmented DM, on the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed. We offset the focal-plane mask in HiCAT, made for an APLC coronagraph, to act as the knife edge for the PAPLC. By defocusing the target acquisition camera installed on HiCAT, we can perform single-image phase retrieval on this camera. As this camera uses only light that is transmitted and filtered by the focal-plane mask, it enables simultaneous wavefront sensing and coronagraphic imaging. We study the capability of this wavefront sensor to recover drifts in piston, tip and tilt on the individual segments on the IrisAO DM installed on HiCAT.

Future space-based coronagraphs will rely critically on focal-plane wavefront sensing and control with deformable mirrors to reach deep contrast by mitigating optical aberrations in the primary beam path. Until now, most focal-plane wavefront control algorithms have been formulated in terms of Jacobian matrices, which encode the predicted effect of each deformable mirror actuator on the focal-plane electric field. A disadvantage of these methods is that Jacobian matrices can be cumbersome to compute and manipulate, particularly when the number of deformable mirror actuators is large. Recently, we proposed a new class of focal-plane wavefront control algorithms that utilize gradient-based optimization with algorithmic differentiation to compute wavefront control solutions while avoiding the explicit computation and manipulation of Jacobian matrices entirely. In simulations using a coronagraph design for the proposed Large UV/Optical/Infrared Surveyor (LUVOIR), we showed that our approach reduces overall CPU time and memory consumption compared to a Jacobian-based algorithm. Here, we expand on these results by implementing the proposed algorithm on the High Contrast Imager for Complex Aperture Telescopes (HiCAT) testbed at the Space Telescope Science Institute (STScI) and present initial experimental and numerical results.

A number of coronagraph designs have been developed for obstructed apertures, but there is a significant performance gap between obstructed and unobstructed apertures. Can this performance gap be closed, or do pupil obstructions and segmentations fundamentally limit coronagraph performance? More generally, how much room for improvement remains for coronagraph designs, both obstructed and unobstructed? We perform a theoretical investigation of these questions. Our methods are based on the approach by Guyon et al. 2006, but we generalize and expand these methods, and apply them to arbitrary apertures. We show that it is theoretically impossible for a coronagraph to perfectly reject a star with a non-0 diameter or be perfectly insensitive to tip/tilt modes. However, arbitrarily good tolerance to stellar angular size can be achieved at the cost of inner working angle, and we provide a fundamental trade relationship linking the two for optimal coronagraphs. We show that the performance of optimal coronagraphs does not strongly depend on aperture obstructions or segmentation, suggesting that the performance gap between obstructed and unobstructed apertures can in theory be mostly closed, with sufficient engineering. We also analyze the performance of optimal coronagraphs in terms of mission yields for LUVOIR and HabEx, and show that optimal coronagraphs improve the science yield by a factor of several, or enable substantial aperture reductions without impacting science yield. Our limits can serve as an ultimate performance target for future coronagraph technology development, as well as to assess the true potential of a given telescope aperture.

The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) mission will directly image debris disks and exozodiacal dust around nearby stars from a high-altitude balloon using a vector vortex coronagraph. The first flight of PICTURE-C launched from the NASA Columbia Scientific Balloon Facility in Ft. Sumner, NM on September 28, 2019 and ew for a total of 20 hours, with 16 hours at float altitude above 110,000 ft. This flight successfully demonstrated many key technologies for exoplanetary direct imaging missions and all hardware components for the second, science-focused flight of PICTURE-C scheduled for the fall of 2021. These technologies include a vector vortex coronagraph, high and low-order deformable mirrors and a high speed low-order wavefront control system. The experiment also demonstrated a 60 cm off-axis telescope with a hexapod-actuated secondary mirror that aligned itself automatically during flight. This paper details the flight performance of PICTURE-C, focusing on the operation of the low-order wavefront control system and the influence of high-frequency structural vibrations. We present new structural modifications that have been made to reduce these vibrations and laboratory demonstrations of the flight 2 coronagraph, which uses a high-order 952 actuator MEMS deformable mirror to create a high-contrast dark zone.

Following the success of the Decadal Survey Testbed (DST), the HCIT team at JPL has developed a companion testbed, the Decadal Survey Testbed 2 (DST2), that further implements lessons learned from DST and from recent modeling work at JPL in support of the HabEx concept. Commissioning for DST2 is currently targeted for Fall 2021. Here we report on the detailed design of DST2 and status of integration and testing highlighting comparisons/changes from the original DST. Expected performance is summarized here, with details of the modeling effort provided in Noyes et al. also in these proceedings.

During days-long exposure of the Roman Space Telescope (RST) Coronographic Instrument (CGI), the starlight wavefront will drift due to thermal instabilities of the optical tube assembly (OTA) and deformable mirror (DM) actuators. While low-order spatial wavefront modes will be sensed upstream of the coronagraph, focal-plane wavefront sensing (FPWS) via DM probing will be used to correct high-order modes. In RST’s nominal operation mode, the high-contrast region of the image (dark hole) will be periodically retouched by pointing at a bright reference star, performing FPWS, correcting the wavefront, and pointing back at the target. We propose instead to continuously probe the DM during the observation, so that the wavefront can be estimated without slewing the telescope. This approach will reduce the risk of introducing OTA instabilities at the expense of slight worsening of the contrast due to the introduction of small DM probes. This work expands previous FPWS methods from single-pixel Extended Kalman Filters (EKF) to an EKF in terms of multiple DM actuators simultaneously. We then evaluate this approach on a numerical model of RST-CGI, based on Observing Scenario (OS) 9. Besides wavefront drift, we also simulate the effects of detector noise associated with photon-counting and line-of-sight jitter. Our results show that it is possible to correct the DM once every 24 hours, without slewing the telescope. This continuous FPWS is compared to periodic slewing based on the planet detection performance in post-processing. In particular, we report similar post-processing errors when doing Angular Differential Imaging after the nominal OS, and Electric Field Order Reduction after continuous dark hole maintenance.

The Nancy Grace Roman Space Telescope (formally WFIRST) will be launched in the mid-2020’s with an onboard coronagraph instrument which will serve as a technology demonstrator for exoplanet direct imaging. The Roman Coronagraph will be capable of detecting and characterizing exoplanets and circumstellar disks in visible light at an unprecedented contrast level of ~10-8 or lower. Such a contrast level, which is several magnitudes better than state-of-the-art visible or near-infrared coronagraphs, raises entirely new challenges that will be overcome using a combination of hardware, calibration and data processing. In particular, the Roman Coronagraph will be the first space-based coronagraphic instrument with real-time active wavefront control through the use of large format deformable mirrors, and its EMCCD detector will enable faint signal detection in photon-counting mode. The Roman Coronagraph instrument passed its critical design review successfully in April 2021, and is now well on its path to demonstrate many core technologies at the levels required for future exo-Earth direct imaging missions.

The Multi-Star Wavefront Control (MSWC) algorithm can be used to suppress scattered light from an off-axis companion star, enabling high-contrast imaging in binary star systems. Applying this technique to the Nancy Grace Roman Space Telescope (Roman, formerly WFIRST) Coronagraph Instrument (CGI) could significantly increase the number of possible targets for the mission. Some of those targets are beyond the deformable mirror spatial Nyquist control zone, and therefore super-Nyquist MSWC would be necessary. In this paper, we present a feasibility analysis of implementing MSWC on Roman CGI.

Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Critical starshade technologies are currently being advanced through the S5 Project and at the Princeton starshade testbed. We report on the conclusion of Milestone 2 of the S5 Project, optical model validation. We present results from optical experiments of starshades with intentional perturbations built into their design. These perturbations are representative of the type of perturbations possible in a flight design and serve as points of validation for diffraction models and error budgets. We show agreement between experiment and diffraction model that meets the Milestone 2 criteria of 25% agreement. We then place these results into the larger context of the design and error budget of a full scale starshade mission. We also present the latest updates to the development of non-scalar diffraction models relevant to the testing of sub-scale starshades. This work completes the optics-focused S5 technology milestones that put starshade technology at TRL 5.

Diffraction and reflection from the optical edges is the dominant source of stray light from a starshade. However, recent progress in optical edge design has led to much reduced predictions in this source. Secondary sources now also play a role; these sources arise from two or more reflections from the starshade structure. These multiple reflections allow light to reach the telescope from parts of the structure that are shaded from direct sunlight. Here we analyze the secondary sources for the starshade model developed as part of the S5 technology development and show the effects of optical edge mechanical design variants and mitigations.

We describe testing and analysis conducted to demonstrate in-space thermoelastic shape stability of starshade structures. Thermoelastic deformation testing was conducted on key starshade structural components. These components were constructed at relevant scales and at relevant fidelity to flight-like structures. Results from thermoelastic deformation testing were used to calibrate high-fidelity finite element structural analysis techniques; these finite element tools were then used to predict the in-space thermoelastic distortions of a 26 m-diameter starshade. The in-space temperatures for these structures were predicted using a separate radiative-thermal finite element simulations, and were meant to envelope temperatures that a starshade would experience during periods of telescope shading. The predicted in-plane thermoelastic deformations of this 26 m-diameter starshade were found to be sufficient to fit into an overall error budget to enable instrument contrast better than 1e-10.

Measuring the astrometric singal of an exoplanet is an unambiguous method for determining its mass. However, Earth-like planets around Sun-like stars only cause 0.3 uas astrometric signals, which is too small for current instruments to detect. To advance these instruments, an astrometry testbed was created. It can simulate and measure equivalent signals with the use of an illuminated pinhole array and a flexurized pinhole that is translatable to 10 pm resolution. Optical distortions are calibrated with the use of a diffractive pupil. This paper presents the requirements, design, and implementation of the wide-field astrometry testbed’s light source.

Accurate measurement of exoplanetary masses is a critical step in addressing key aspects of NASA’s science vision. Astrometry can detect and measure masses of planets orbiting the target star. However, the signal for earth-analogs is in the sub-microarcsecond regime, well beyond our instrumentation. In this paper, we study part of an astrometry error budget for the HabEx Workhorse Camera and we propose a calibration approach to reach earth-analog sensitivity.

High contrast imaging (HCI) systems rely on active wavefront control (WFC) to deliver deep raw contrast in the focal plane, and on calibration techniques to further enhance contrast by identifying planet light within the residual speckle halo. Both functions can be combined in an HCI system and we discuss a path toward designing HCI systems capable of calibrating residual starlight at the fundamental contrast limit imposed by photon noise. We highlight the value of deploying multiple high-efficiency wavefront sensors (WFSs) covering a wide spectral range and spanning multiple optical locations. We show how their combined information can be leveraged to simultaneously improve WFS sensitivity and residual starlight calibration, ideally making it impossible for an image plane speckle to hide from WFS telemetry. We demonstrate residual starlight calibration in the laboratory and on-sky, using both a coronagraphic setup, and a nulling spectro-interferometer. In both case, we show that bright starlight can calibrate residual starlight.

A key challenge of high contrast imaging (HCI) is to differentiate a speckle from an exoplanet signal. The sources of speckles are a combination of atmospheric residuals and aberrations in the non-common path. Those non-common path aberrations (NCPA) are particularly challenging to compensate for as they are not directly measured, and because they include static, quasi-static and dynamic components. The proposed method directly addresses the challenge of compensating the NCPA. The algorithm DrWHO - Direct Reinforcement Wavefront Heuristic Optimisation - is a quasi-real-time compensation of static and dynamic NCPA for boosting image contrast. It is an image-based lucky imaging approach, aimed at finding and continuously updating the ideal reference of the wavefront sensor (WFS) that includes the NCPA, and updating this new reference to the WFS. Doing so changes the point of convergence of the AO loop. We show here the first results of a post-coronagraphic application of DrWHO. DrWHO does not rely on any model nor requires accurate wavefront sensor calibration, and is applicable to non-linear wavefront sensing situations. We present on-sky performances using a pyramid WFS sensor with the Subaru coronagraph extreme AO (SCExAO) instrument.

Recent evolutions in high contrast imaging have shed light on intrinsic limitations of general purpose adaptive optics (AO) systems. In particular, the low wind and petaling effects (LWE, PE), caused by the discontinuous apertures of telescopes, are poorly corrected, if at all, by commonly used wavefront sensors (WFSs). This results in large differential piston aberrations between the disjointed portions of the clear aperture. The LWE/PE decoheres the PSF core, generating multiple side lobes, and dramatically shuts off coronagraphic capabilities. We demonstrate the re-purposing of non-redundant sparse aperture masking (SAM) interferometers into low-order WFSs complementing the high-order pyramid WFS, on the SCExAO experimental platform at Subaru Telescope. The SAM far-field interferograms are used for direct retrieval of PE aberrations, which are invisible to the main AO loop. We show that this technique allows for a high-sensitivity, high-precision wavefront control loop, down to illuminations of a few hundreds of photons per frame.

Extreme adaptive optics (AO) is crucial for enabling the contrasts needed for ground-based high contrast imaging instruments to detect exoplanets. Pushing exoplanet imaging detection sensitivities towards lower mass, closer separations, and older planets will require upgrading AO wavefront sensors (WFSs) to be more efficient. In particular, future WFS designs will aim to improve a WFS’s measurement error (i.e., the wavefront level at which photon noise, detector noise, and/or sky background limits a WFS measurement) and linearity (i.e., the wavefront level, in the absence of photon noise, aliasing, and servo lag, at which an AO loop can close and the corresponding closed-loop residual level). We present one such design here called the bright pyramid WFS (bPWFS), which improves both the linearity and measurement errors as compared to the non-modulated pyramid WFS (PWFS). The bPWFS is a unique design that, unlike other WFSs, doesn’t sacrifice measurement error for linearity, potentially enabling this WFS to (a) close the AO loop on open loop turbulence utilising a tip/tilt modulation mirror (i.e., a modulated bPWFS; analogous to the procedure used for the regular modulated PWFS), and (b) reach deeper closed-loop residual wavefront levels (i.e., improving both linearity and measurement error) compared to the regular non-modulated PWFS. The latter approach could be particularly beneficial to enable improved AO performance using the bWFS as a second stage AO WFS. In this paper we will present an AO error budget analysis of the non-modulated bPWFS as well as supporting AO testbed results from the Marseille Astrophysics Laboratory.

The search for exoplanets is pushing adaptive optics systems on ground-based telescopes to their limits. A major limitation is the temporal error of the adaptive optics systems. The temporal error can be reduced with predictive control. We use a linear data-driven integral predictive controller that learns while running in closed-loop. This is a new algorithm that has recently been developed. The controller is tested in the lab with MagAO-X under various conditions, where we gain several orders of magnitude in contrast compared to a classic integrator. With the current schedule, the new data-driven predictive controller will be tested on-sky in spring 2021. We will present both the lab results and the on-sky results, and we will show how this controller can be implemented with current hardware for future extremely large telescopes.

The Santa Cruz Extreme AO Lab (SEAL) is a new visible-wavelength testbed designed to advance the state of the art in wavefront control for high contrast imaging on large, segmented, ground-based telescopes. SEAL provides multiple options for simulating atmospheric turbulence, including a custom spatial light modulator. A 37-segment deformable mirror simulates the W. M. Keck Observatory segmented primary mirror. The adaptive optics system consists of a woofer/tweeter DM system, and four wavefront sensor arms: 1) a high-speed Shack-Hartmann WFS, 2) a reflective pyramid WFS, 3) vector-Zernike mask, and 4) a Fast Atmospheric SCC Technique demonstration arm. Finally, a science arm preliminarily includes a classical Lyot-style coronagraph. SEAL's real time control system is based on the CACAO package, and is designed to support the efficient transfer of software between SEAL and the Keck II AO system. In this paper, we present an overview of the design and first light performance of SEAL.

High quality, repeatable point-spread functions are important for science cases like direct exoplanet imaging, high-precision astrometry, and high-resolution spectroscopy of exoplanets. For such demanding applications, the initial on-sky point-spread function delivered by the adaptive optics system can require further optimization to correct unsensed static aberrations and calibration biases. We investigated using the Fast and Furious focal-plane wavefront sensing algorithm as a potential solution. This algorithm uses a simple model of the optical system and focal plane information to measure and correct the point-spread function phase, without using defocused images, meaning it can run concurrently with science. On-sky testing demonstrated significantly improved PSF quality in only a few iterations, with both narrow and broadband filters. These results suggest this algorithm is a useful path forward for creating and maintaining high-quality, repeatable on-sky adaptive optics point-spread functions.

We present the results from our predictive wavefront control algorithm tested using the near-infrared pyramid wavefront sensor on the Keck II adaptive optics (AO) bench. The algorithm aims to minimise the servo-lag error of the AO system. We compare the achieved contrast for a vortex coronagraph for both the predictive control algorithm and the standard integral control law.

The detection and characterization of Earth-like exoplanets is one of the major science drivers for the next generation of telescopes. Current direct imaging instruments are limited by evolving Non Common Path Aberrations (NCPA). A promising sensor is the Self Coherent Camera (SCC) that uses a pinhole in the Lyot plane to modulate the focal plane electric field. However, the SCC has low throughput due to the large separation between the pinhole and the edge of the pupil. The spectrally modulated Self Coherent Camera solves this issue by modulating the pinhole along the spectral direction. The SM-SCC can place the pinhole directly at the edge of the pupil which increases the throughput by a factor of 100. This allows the SM-SCC to go faster or use it on fainter objects that the SCC. Here we present the concept of the SM-SCC and show that it can be used for focal plane wavefront control, Coherence Differential Imaging (CDI) and Spectral Differential Imaging (SDI).

Current and future high contrast imaging instruments aim to detect exoplanets at closer orbital separations, lower masses, and/or older ages than their predecessors, with the eventual goal of directly detecting terrestrial-mass habitable-zone exoplanets. However, continually evolving speckles in the coronagraphic science image still limit state-of-the-art ground-based exoplanet imaging instruments to contrasts at least two orders of magnitude worse than what is needed to achieve this goal. For ground-based adaptive optics (AO) instruments it remains challenging for most speckle suppression techniques to attenuate both the dynamic atmospheric and quasi-static instrumental speckles. We have proposed a focal plane wavefront sensing and control algorithm to address this challenge, called the Fast Atmospheric Self-coherent camera (SCC) Technique (FAST), which enables the SCC to operate down to millisecond timescales even when only a few photons are detected per speckle. Here we present preliminary experimental results of FAST on the Santa Cruz Extreme AO Laboratory (SEAL) testbed, demonstrating closed-loop focal plane wavefront control on millisecond-timescales.

We explore the high contrast capabilities of large segmented telescopes with Active and Adaptive Optics, with particular focus on a system view, which includes use of approaches that are routine for current large ground-based telescopes. These approaches include continuous Wavefront Sensing and control (WFS&C), and proper partitioning of engineering challenges by optimizing the error budget allocations. We present a methodology to compute wavefront stability requirements in the presence of temporal variations of the observatory optical errors at all spatial scales: global low order aberrations, segment to segment misalignments and high spatial frequencies. We start by deriving the sensitivity of the starlight suppression of a coronagraph instrument (e.g. the relationship between contrast and wavefront variance) for each family of spatial modes. We then propagate open loop wavefronts variances, alongside with the actual photons carrying the information associated with these misalignments, through diffractive linear wavefront sensor models. We calculate the Fisher information of measurements using those. That quantity is then used in the context of a Cramer-Rao bound to evaluate closed loop residuals, which are then propagated through coronagraph models to yield contrast fundamental limits. Working under the assumption that such WFS&C systems will be limited by the information content bottleneck due to the finite magnitude of a natural guide star, we use results from these calculations to quantify observatory requirements for a variety of exoplanet imaging missions. We highlight the similarities and differences between monolithic and segmented architectures, and show that the often-cited need for picometer stability is no longer required for the latter across the full aperture, but rather within combinations of segments. We also consider both the case of batch and recursive wavefront estimators (that take into account the entire sensing history) and make the case for significantly less challenging observatory requirements when the latter class of algorithms is implemented.

Future planned space telescopes such as HabEx and LUVOIR will be used to directly image exo-Earths. These telescopes use coronagraph instruments to suppress starlight and resolve dim exoplanets. They will employ high order wavefront sensing and control (HOWFSC) to correct static and slow wavefront errors in the image plane to achieve contrasts above 10⁹. This work evaluates architectures to meet the computational requirements for HOWFSC algorithms with available processors. We find that the computational requirements of HOWFSC will impose unprecedented requirements on space-based components and that typical combinations of computational resource and control architecture will consume significant observation time. Science yield from the space telescope can be improved, and mission risk and cost reduced, by using co-flying or ground-in-the loop computational offload architectures. In particular, a high-capability co-flying processor could use commercial components 10⁴ times more powerful than typical radiation hardened options. This would enable key HOWFSC algorithms to run in seconds rather than hours or days, removing operational constraints on the science mission. While commercial processors may be more susceptible to total ionizing dose radiation effects over the expected mission lifetime of 5-10 years, the relatively low cost of development and replacement launches make these co-flying processors an attractive option. We evaluate three major co-flying architecture trades: (i) inter-spacecraft distance, (ii) risk classification, and (iii) processor selection. We find that one or more low-cost replaceable co-flying processors with COTS components and flying several kilometers from the telescope spacecraft can provide all needed computation.

Due to the limited number of photons, directly imaging planets requires long integration times with a coronagraphic instrument. The wavefront must be stable on the same time scale, which is often difficult in space due to thermal variations and other mechanical instabilities. In this paper, we discuss the implications on future space mission observing conditions of our recent laboratory demonstration of a dark hole maintenance (DHM) algorithm. The experiments are performed on the High-contrast imager for Complex Aperture Telescopes (HiCAT) at the Space Telescope Science Institute (STScI). The testbed contains a segmented aperture, a pair of deformable mirrors (DMs), and a lyot coronagraph. The segmented aperture injects high order zernike wavefront aberration drifts into the system which are then corrected by the DMs downstream via the DHM algorithm. We investigate various drift modes including segmented aperture drift, all DMs drift, and drift correction at multiple wavelengths.

One of the primary science goals of the Large UV/Optical/Infrared Surveyor (LUVOIR) mission concept is to detect and characterize Earth-like exoplanets around nearby stars with direct imaging. The success of its integrated instrument ECLIPS (Extreme Coronagraph for Living Planetary Systems) depends on the ability to stabilize the wavefront from a large segmented mirror at a level of a few picometers during an exposure time of a few hours. To relax the constraints on the mechanical stability, ECLIPS will be equipped with a wavefront sensing and control (WS&C) architecture to correct wavefront errors at high temporal frequencies (<~1 Hz). These errors are expected to be dominated by spacecraft structural dynamics exciting vibrations at the segmented primary mirror. In this work, we present detailed simulations of the WS&C system within the ECLIPS instrument and the resulting contrast performance. This study assumes realistic wavefront aberrations based on a Finite Element Model of the telescope and the spacecraft structural dynamics. Wavefront residuals are then computed according to a model of the adaptive optics system that includes numerical propagation to simulate realistic images on the wavefront sensor and an analytical model of the temporal performance. An end-to-end numerical propagation model of ECLIPS is then used to estimate the residual starlight intensity distribution on the science detector. We show that the contrast performance depends strongly on the target star magnitude and advocate for the use of laser metrology to mitigate high temporal frequency wavefront errors and increase the mission yield.

Future large segmented space telescopes and their coronagraphic instruments are expected to provide the resolution and sensitivity to observe Earth-like planets with a 10¹⁰ contrast ratio at less than 100 mas from their host star. Advanced coronagraphs and wavefront control methods will enable the generation of high-contrast dark holes in the image of an observed star. However, drifts in the optical path of the system will lead to pointing errors and other critical low-order aberrations that will prevent maintenance of this contrast. To measure and correct for these errors, we explore the use of a Zernike wavefront sensor (ZWFS) in the starlight rejected and filtered by the focal plane mask of a Lyot-type coronagraph. In our previous work, the analytical phase reconstruction formalism of the ZWFS was adapted for a filtered beam. We now explore strategies to actively compensate for these drifts in a segmented pupil setup on the High-contrast imager for Complex Aperture Telescopes (HiCAT). This contribution presents laboratory results from closed-loop compensation of bench internal turbulence as well as known introduced aberrations using phase conjugation and interaction matrix approaches. We also study the contrast recovery in the image plane dark hole when using a closed loop based on the ZWFS.

We present a segment-level wavefront stability error budget for the LUVOIR A architecture essential for exoplanet detection. We start with a detailed finite element model to relate the temperature and gravity gradients at the location of the primary mirror to wavefront variations for each segment, and propagate the elements through a diffractive model of the observatory and coronagraphic instrument. Segment level errors are measured via a model of the WFS&C architecture in combination with a Zernike phase sensor and science camera. These sensitivities are used to relate semi-analytically the open and closed loop variance of the segments’ thermo-mechanical modes.

Although only a small fraction of currently known exoplanets was found in binary and multiple systems, studies show that such stars do form planets, with an efficiency that is smaller, but within an order of magnitude of single stars. However, binaries are rarely considered as targets for exoplanet imaging space missions because of challenges of removing light from the second binary component. In our previous works it was shown how to solve two main issues that make exoplanet imaging in multiple systems impossible, namely, the mutual incoherence of speckles created by different binary components, and inability of a deformable mirror (DM) to control the starlight beyond the DM outer working angle/Nyquist limit. Feasibility of the developed Multi-Star Wavefront Control (MSWC) and Super-Nyquist Wavefront Control (SNWC) algorithms was demonstrated at the Ames Coronagraph Experiment (ACE) laboratory using a simple imaging system with a DM and no coronagraph. In this paper, we report the results our MSWC experiments using the Subaru Coronagraphic Extreme Adap- tive Optics (SCExAO) instrument that is part of our technology development effort. The main goal of these experiments is to validate MSWC on a real coronagraphic system by using an internal source to simulate at least one real representative binary target. In our demonstration narrow-band contrast of 4.1 × 10⁻⁶ has been reached by using MSWC in a 12 × 6λ/D dark zone separated from the primary component of the simulated binary star (STF 3121 AB) by 4λ/D. This contrast is better by a factor of 13.2 than the contrast floor reached by standard single-star wavefront control (SSWC). We also discuss the main limiting factors that affect the MSWC performance in our experiments.

In order to characterize exoplanets around nearby stars, upcoming and proposed space telescopes are being designed with high contrast coronagraph instruments. Coronagraphs are generally designed to suppress only a single, on-axis star, but there are numerous binary star systems within our observational range. Multi-star wavefront correction (MSWC) is a technique that leverages non-redundant control modes around two stars to create a single dark zone in the image. In this paper we describe the implementation of MSWC in the Decadal Survey Testbed (DST) at the Jet Propulsion Laboratory. We modified the open-source FALCO software package, which is used to run the DST, to enable sensing and control of multiple sources. To enable MSWC at large (i.e., super-Nyquist) angular separations, we modified the DST calibration procedure. We report our best achieved contrast and planned modifications to complete our future milestones.

The characterization of exoplanets’ atmospheres using direct imaging spectroscopy requires high-contrast over a wide wavelength range. We study a recently proposed focal plane wavefront estimation algorithm that exclusively uses broadband images to estimate the electric field. This approach therefore reduces the complexity and observational overheads compared to traditional single wavelength approaches. The electric field is estimated as an incoherent sum of monochromatic intensities with the pair-wise probing technique. This paper covers the detailed implementation of the algorithm and an application to the High-contrast Imager for Complex Aperture Telescopes (HiCAT) testbed with the goal to compare the performance between the broadband and traditional narrowband filter approaches.

Advancements in high-efficiency variable reluctance actuators are an enabling technology for building the next generation of large-format deformable mirrors, including adaptive secondary mirrors. The Netherlands Organization for Applied Scientific Research (TNO) has developed a new style of hybrid variable-reluctance actuator that requires approximately seventy-five times less power to operate as compared to the traditional style of voice-coil actuators. We present the initial performance results from laboratory testing of TNO's latest 19-actuator prototype mirror, FLASH. We report the linearity, hysteresis, natural shape flattening, actuator cross-coupling, creep, and repeatability of the FLASH prototype and compare the results to previous TNO prototype deformable mirrors. We also present results of the performance of FLASH on sub-millisecond timescales in order to estimate the limits for the use of this technology when utilized to perform high-contrast imaging adaptive optics.

After completing its duty in one the vacuum chambers in the High Contrast Imaging Testbed (HCIT) facility at NASA’s Jet Propulsion Laboratory, the General Purpose Coronagraph Testbed (GPCT) has been retrofitted as the In-Air Coronagraph Testbed (IACT), with the purpose of verification of Boston Micromachines (BMC) 50x50 MEMS deformable mirrors (MEMS DM) performance by contrast comparison before and after random vibration testing. The testbed is configured as a vortex coronagraph, with one MEMS DM in the pupil plane to create a half dark hole in monochromatic light. High wavefront stability is achieved using an environmentally isolating enclosure, based on the enclosure design previously used on Caltech’s High Contrast Spectroscopy Testbed (HCST).

The vector vortex coronagraph (VVC) is a leading choice for future space-based exoplanet direct imaging missions due to its simplicity and high throughput. The construction of the VVC as an azimuthally rotating half-wave plate implies a differential influence on the two orthogonal circular polarization states of incident starlight - particularly on the mapping of deformable mirror (DM) actuators to the final image plane. Traditional electric field conjugation (EFC) coupled with the VVC is capable of digging a high-contrast dark zone in one circular polarization, but the dark zone is not preserved in the orthogonal state. This paper presents an extension to the traditional EFC algorithm to find DM actuator solutions that produce a dark zone simultaneously in both circular polarizations. This dual-polarization EFC can be used in conjunction with low-leakage VVC architectures to perform high-contrast polarimetric measurements using a single coronagraph.

In the Bavarian Alps, an optimal exoplanet follow-up device is located. Besides a 43cm telescope for long term photometric observations, the observatory operates the 2.1m Fraunhofer Telescope Wendelstein, which is equipped with the highly temperature- and pressure-stabilized, frequency comb calibrated Échelle spectrograph MaHPS (R ∼ 65000) to conduct radial velocity measurements. Further, the 3KK instrument is able to conduct multiband photometry with its two Apogee-ALTA F3041 cameras for optical and its H2RG CMOS for NIR light, discerning different transit scenarios, since the characteristics of limb darkening cause differing eclipse depths and shapes, depending on the nature of the system. The combination of the photometric and spectroscopic observations allow for confident confirmation or discarding of exoplanetary candidates.

Santa Cruz Array of Lenslets for Exoplanet Spectroscopy (SCALES) is an instrument being designed for direct imaging of exoplanets in the mid-infrared with the Adaptive Optics System of the W.M. Keck Observatory. The performance of SCALES will be largely affected by thermal emission from the instrument structures. Placement of a pupil stop can limit the emission of instrument structures such as primary mirror segment gaps, secondary structures, and spider arms. Here we proposed a cold stop design of a circular inner mask paired with a serrated outer mask. Taking into account the pupil nutation, we modeled the throughput and the background emission for the design to optimize the dimensions of the cold stop.

We present preliminary laboratory cryogenic test results for the Coronagraph Slide mechanism, which allows observers the choice of up to 4 coronagraphic focal plane masks when using SCALES (Santa Cruz Array of Lenslets for Exoplanet Spectroscopy). SCALES is a 2-5 micron high-contrast lenslet integral field spectrograph currently undergoing preliminary design for the W. M. Keck Observatory. When deployed behind the Keck Adaptive Optics system, SCALES will be used to detect and characterize a wide variety of exoplanets. To minimize thermal emission, all optical and mechanical components of SCALES are fully cryogenic. The Coronagraph Slide is the first fully cryogenic mechanism for SCALES designed, built, and tested in-house at UCSC with mostly off-the-shelf components.

We present an exposure time calculator (ETC) developed for polarimetric observing modes for two next-generation high-contrast direct imaging instruments planned for the W. M. Keck Observatory: SCALES1 (Santa Cruz Array of Lenslets for Exoplanet Spectroscopy), a low-resolution mid-infrared integral field spectrograph; and a future polarimetric observing mode for NIRC2, the near-infrared adaptive optics (AO) supported high-contrast direct imager currently on the Keck Observatory. In addition to producing estimates of companion signal-to-noise ratios (SNR, see Fig. 2a), the ETC calculates the polarization fraction that would be detected with a user-specific SNR in a given exposure time (see Fig. 2b). The ETC includes a graphical user interface and is packaged as a polarimetry add-on to the PSI-Red thermal imaging module of PSISim, an instrument performance simulation tool for the Planetary Systems Imager2 - a modular suite of AO-supported instruments planned for the Thirty Meter Telescope

The Nancy Grace Roman Space Telescope, planned to launch in the mid-2020s, will be the first space-based observatory to demonstrate active wavefront correction at high contrast with its Coronagraph Instrument. As a technology demonstrator, the instrument’s main purpose is to mature the various technologies needed by future flagship mission concepts that aim to image and characterize Earth-like exoplanets. These technologies include two high-actuator-count deformable mirrors (DMs), photon-counting detectors, two complementary wavefront sensing and control loops, and two different coronagraph types. Here we describe the complete set of flight mask designs for the Roman Coronagraph. Multiple mask configurations are required to overcome the challenging pupil obscurations and enable the desired types of imaging, spectroscopy, and polarimetry. In designing each mask configuration, we considered many performance metrics, including spectral bandwidth, field of view, contrast, core throughput, encircled energy, deformable mirror surface height, and low-order aberration sensitivity