The HabEx and LUVOIR mission concepts aim to directly image and spectrally characterize potentially habitable exoplanets. We use EXOSIMS to simulate design reference missions with observation scheduling to determine yield of exoplanets detected, spectrally characterized, and orbits determined. EXOSIMS performs dynamically responsive scheduling with realistic mission observing constraints on Monte Carlo universes of synthetic planets around known nearby stars. We use identical astrophysical inputs and the individual observing scenarios of each concept to evaluate a common comparison of the detection and spectral characterization yields of HabEx and LUVOIR. HabEx is evaluated for the 4m hybrid starshade and coronagraph architecture, the 4m coronagraph only architecture, and the 3.2 m starshade only architecture. LUVOIR is evaluated for the 15 m architecture presented in their interim report and the 9 m architecture of their final report. Yield analysis shows that both concepts can directly image and spectrally characterize earth-like planets in the habitable zone and that each concept has complementary strengths.

Future space missions such as the Large UV-Optical-Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Observatory (HabEx) require coronagraphs with active wavefront control to suppress starlight to discover and characterize habitable exoplanets. The Extreme Coronagraph for Living Planetary Systems (ECLIPS) is the coronagraph instrument on the LUVOIR Surveyor mission concept, an 8{15m segmented telescope. ECLIPS is split into three channels: UV (200 to 400 nm), optical (400 nm to 850 nm), and NIR (850 nm to 2.0 microns), with each channel equipped with two deformable mirrors for wavefront control, a suite of coronagraph masks, a low-order/out-of-band wavefront sensor, and separate science imagers and spectrographs. The Apodized Pupil Lyot Coronagraph (APLC) and the Vector Vortex Coronagraph (VVC) are the baselined mask technologies for ECLIPS to enable the required 10^-10 contrast for observations in the habitable zones of nearby stars. Their performance depends on active wavefront sensing and control, as well as metrology subsystems to compensate for aberrations induced by segment errors (piston and tip/tilt, among others), secondary mirror misalignment, and global low-order wavefront errors. Here we present the latest results of the simulation of these effects for the two technologies and discuss the achieved contrast for exoplanet detection and characterization after closed-loop wavefront estimation and control algorithms have been applied. Finally, we show simulated observations using high-fidelity spatial and spectral input models of complete planetary systems generated with the Haystacks code framework.

Detection and characterization of Earth-like planets around nearby stars using the direct imaging technique is a key scientific objective of future NASA astrophysics flagship missions. As a result, dedicated exoplanet instruments are being studied for the Large UV/Optical/Infrared Surveyor (LUVOIR) and the Habitable Exoplanet Imager (HabEx) mission concepts. In this paper we discuss the Extreme Coronagraph for Living Planetary Systems (ECLIPS) instrument of LUVOIR. ECLIPS will be capable of providing starlight suppression levels of ten orders of magnitude over a broad range of wavelengths in order to detect and characterize the light reflected from potentially Earth-like planets. It will also allow future astronomers to study in great detail the diversity of exoplanets. First, we review the main science drivers and emphasize those that are the most stressing on the instrument design. We then present the overall parameters of the instrument (general architecture and back-end camera). We delve into the details of the static coronagraph masks, which have a significant impact on the scientific productivity of the mission. We discuss the choices the LUVOIR team made in order to maximize the discovery yield of exoEarth candidates. We then present our work on the technological feasibility of such an instrument, focusing in particular on the image stability necessary to achieve ten orders of magnitude of starlight extinction over hours of exposure. We present our error budget and show that using a combination of instrument level (low and high order wavefront sensors) and observatory level telemetry can yield an overall architecture that meets these requirements. Finally, we discuss future technology development efforts that will mature these technologies.

The HabEx study has developed a baseline concept for a 4 m aperture next generation space telescope operating from the ultraviolet to the infrared, capable of compelling general astrophysics and exoplanet science. HabEx carries four instruments, a UV spectrometer/imager (UVS) together with a general purpose astrophysics camera/spectrograph (HWC) and for exoplanet work, a coronagraph and a starshade. UVS reaches down to 115 nm with resolution up to 60,000 and a 3’x3’ field of view. HWC operates between 370 nm and 1800 nm, again with a 3’x3’ field of view; the spectral resolution is 1000 and it carries a suite of science filters. The telescope is capable of tracking both deep space and solar system objects. The coronagraph enables observations and spectroscopy at up to R=140 with instantaneous 20% bandwidth between wavelengths of 450 and 1800 nm and is intended to be used in a survey mode. However, it also backs up most of the functionality of the accompanying starshade instrument which will have superior performance for spectroscopy. The 52 m diameter starshade flies 76,600 km from the telescope and at that range has a broadband suppression of the starlight between 300 and 1000 nm. A single observation at 108% bandwidth covers a very wide spectral band at a resolution up to 140. Both coronagraph and starshade are equipped with integral field spectrometers to enable simultaneous spectroscopy of exoplanets within the field of view. This paper details the design of the telescope, the four science instruments and associated optical systems.

The Habex study, commissioned by NASA in preparation for the 2020 Decadal Survey, is evaluating a 4 meter space telescope for high contrast imaging and spectral characterization of extrasolar terrestrial planets. Its off-axis configuration, active structural metrology, and low-disturbance pointing control provide an optimal system for coronagraphs. We present predictions of the Habex performance using a charge 6 vortex coronagraph that have been obtained using numerical modeling techniques developed for the WFIRST coronagraph. The models include realistic optical surface and polarization-induced aberrations, pointing jitter, and thermally-induced wavefront variations. Wavefront control using dual deformable mirrors is simulated to create a dark, high-contrast hole around the star. The results show that current technologies can closely approach the Habex performance goals, and with some additional development in key areas (e.g., deformable mirror surface quality, low-polarization coatings, etc.) over the next few years they should reliably meet them.

The history and application of ZERODUR® toward availability of 4-meter monolithic blanks for astronomical telescopes is summarized. Features of ZERODUR® are both its near-zero coefficient of thermal expansion with extraordinary homogeneity, and that the mirror substrate is monolithic as cast: No joining is involved. CNC machining at the SCHOTT AG facility now can fully address all shape factors of 4-meter blanks. This shaping is via efficient CNC fixed abrasive grinding. Significant improvements have been made to both the specular figure form, while minimizing sub-surface damage. These CNC methods are also used to do a high degree of lightweighting behind the face sheet of the mirror. We describe the expected material availability and lead time. Monolithic large precision mirror blanks of ZERODUR® offer performance advantages unmatched among mirror substrate materials.

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 was recently rescheduled by NASA for September, 2019. This paper describes preparations for the first flight of PICTURE-C, including the final mission design, flight integration process and observation plan. Laboratory measurements of the low-order wavefront control system and coronagraph performance are also presented.

Direct imaging of Earth-like exoplanets in reflected starlight requires high contrast imaging systems, such as coronagraph, with starlight suppression better than 1e-10 over a broad spectral band. Such deep contrast can only be achieved by means of wavefront control techniques (e.g. speckle nulling, electric field conjugation, stroke minimization…) where deformable mirrors correct for low and mid-frequency optical aberrations. In space, the coronagraph with wavefront control will create high contrast regions using a target star before pointing to a science star. While re-pointing the space-telescope, the surface stability of the deformable mirrors will play a very important role in maintaining the high contrast regions. In the present work, we report an optical characterization and stability analysis of MEMS deformable mirrors for high contrast imaging using a vortex coronagraph in vacuum to simulate space conditions. We created high contrast regions using electric field conjugation and monitored its evolution for several hours using pair-wise estimation.

The Wide Field Infrared Survey Telescope (WFIRST), which is planned for launch in 2025, is NASA’s next large space observatory after the James Webb Space Telescope. It contains two primary science instruments: A Wide Field Instrument (WFI) to carry out surveys of galaxies in the near infrared; explore the properties of dark energy and dark matter; and carry out a microlensing survey to complete the census of exoplanets, and a Coronagraph Instrument (CGI) to demonstrate high-contrast technology for exoplanet imaging and spectroscopy. Understanding how to implement the technology for CGI is a critical step toward future, larger missions targeted at direct imaging of Earthlike planets in the habitable zone of nearby stars. This paper presents an overview of the current instrument design and requirements, highlighting the critical technologies being demonstrated. These include two types of coronagraphs, closed-loop wavefront control with two deformable mirrors, a visible-light, electron multiplying detector (EMCCD), and a lenslet based integral field spectrograph. Additionally, critical algorithms will be developed and tested for low- and high-order wavefront control, spectral extraction, and post-processing for planet detection. The paper will also describe the operational plans for the instrument. A participating scientist program (PSP) will enable members of the community to engage in the technology demonstration and, if warranted by instrument performance, will incorporate science focusing on imaging and spectra of large Jupiter size planets and protoplanetary and debris disks and a blind search program for undiscovered Jupiters and possibly mini-Neptunes.

The WFIRST Coronagraph Instrument will perform direct imaging of exoplanets via coronagraphy of the host star. The Phase B optical design fits within a new allocated instrument enclosure and accommodates both Hybrid Lyot and Shaped Pupil coronagraphs. It provides optical path and space for accessible focal planes for occulting masks and field stops. It provides accessible pupil planes for shaped pupil and Lyot masks. It accommodates ten active optical assemblies, including one fast steering mirror, on focusing mirror, two deformable mirrors, and six precision alignment mechanisms. We present the optical design and analyses for the Direct Imaging channel, including polarization imaging. We also present the performance analysis of pupil imaging for starlight illumination and diffused light illumination of the pupil.

The principal science goal of directly imaging exoplanets is spectroscopy. Future mission concepts such as LU- VOIR and HabEx have baselined their science instruments to use an integral field spectrograph (IFS) to maximize observing efficiency. Coronagraphic imaging with an IFS has strong heritage at ground observatories, having produced planet and brown dwarf near-infrared spectra at contrast floors as low as high 1 × 10^-6 levels. As a technology demonstration for future missions the WFIRST coronagraph instrument (CGI) will demonstrate the ability to measure spectra in visible light with at contrast levels sufficient for detecting Earth-like planets. The spectrograph was originally meant to match that of future missions; an independent IFS channel for wavefront control and imaging spectroscopy. Due to a series of de-scopes as the project progressed, the baseline spectroscopic capability of CGI is no longer an IFS but a zero deviation optical prism and slit used in conjunction with the direct imaging camera. Regardless, CGI advanced a lenslet IFS through the preliminary design phase of a flight project. Here we present that development as the challenges and requirements of an IFS for coronagraphy are quite unique and relevant to future missions. With that development in place, we also present the initial design of the zero optical deviation prism, highlighting the relative challenges and performance of each concept.

The Wide Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI) is a high-contrast imager and integral field spectrograph that will enable the study of exoplanets and circumstellar disks at visible wavelengths. Future flagship mission concepts aim to image Earth analogues with visible light flux ratios greater than 10^10, and CGI is a critical intermediate step toward that goal. CGI will have ~3 months of observing time during the first 18 months of the mission (its "tech demo phase") to demonstrate its technology objectives and to determine whether its as-built performance justifies additional science observing time during the remainder of the mission. We present the CGI portion of the preliminary WFIRST Design Reference Mission (DRM). We describe the suite of anticipated observing and calibration tasks, the preliminary target list, and a schedule with realistic observing constraints and exposure times. We expect that during the tech demo phase CGI will image multiple planets and circumstellar disks in reflected light and take a spectrum of a mature Jupiter analog in reflected light. Furthermore, CGI is expected to be more sensitive than any previous instrument to extrasolar zodiacal dust and has the potential to study very young (proto)planetary systems.

To image and spectrally characterize exoplanets in the coming decades, coronagraphs are being developed for several high-contrast, space-based mission concepts. The first planned mission is the Wide-Field Infrared Survey Telescope (WFIRST) Coronagraph Instrument (CGI), which will demonstrate key coronagraphic technologies for the first time in space. Early research on WFIRST coronagraph designs focused on overcoming diffraction from the large pupil obscurations. Our latest work has been to optimize coronagraphs at the system level, making them more robust to low-order aberrations from telescope dynamics and polarization aberrations. In this paper, we show how to modify coronagraph optimization formulations to directly suppress sensitivities to low-order Zernike modes, in particular tip/tilt. We find and characterize the trade between throughput and tip/tilt sensitivity for shaped pupil Lyot coronagraphs. For coronagraph designs using deformable mirrors, we find that tip/tilt sensitivity can be improved by one to two orders of magnitude at small working angles without sacrificing any throughput. These results may help WFIRST to overcome residual pointing jitter from its reaction wheels and future large-aperture observatories to be less sensitive to resolved stellar diameters.

The WFIRST Coronagraph uses a Low-Order Wavefront Sensing and Control (LOWFS/C) subsystem to stabilize the stellar wavefront. This is true for the Hybrid Lyot Coronagraph (HLC), the Shaped Pupil Coronagraph (SPC) spectrograph, and the SPC wide field of view modes. For the SPC spectrograph, we have found via modeling and simulations that a focal plane mask (FPM) with an elliptical phase dimple can reduce the LOWFS errors significantly compared to the conventional, circular phase dimple. For HLC designs, we concurrently optimized the FPM parameters and deformable mirror shapes using our open-source software toolbox, the Fast Linearized Coronagraph Optimizer (FALCO). This process resulted in new FPMs with non-uniform central-area phase modulation. We have found in numerical simulations that such FPMs still provide sufficient LOWFS performance. In this paper, we will present the LOWFS performance for several new HLC and SPC FPM designs.

Occulter mask fabrication for Hybrid Lyot Coronagraph (HLC) at JPL is a relatively mature technology as past successful testbed demonstrations can attest. Nevertheless, as NASA’s WFIRST mission moved into Phase B, new mask design space and fabrication process were explored for new requirements and for better performances for the CoronaGraph Instrument (CGI). To minimize the risks associated with the new explorations, CGI modeling team is tasked with assessing the viability of new designs. In this paper, we describe our HLC modeling effort and results, which identified the potential risks with early exploratory designs and modified fabrication processes. As a result, the traditional (proven) style design is kept for risk aversion. Along the way a standard procedure has been developed for systematic mask evaluation, mask baselining, and general flight performance prediction. In the second part, we describe our model validation effort for the chosen baseline mask’s testbed performance. The focus of the testbed demonstration is to address a major concern related to the CGI’s limited time for wavefront control (WFC) in flight. It includes two stages of WFC: ground seed generation WFC, and (simulated) in-orbit commissioning phase WFC. Good agreements have been achieved in both stages of WFC which affirms that the CGI is capable of digging a dark hole that meets raw contrast requirement within the required time allocation. It also represents a significant improvement in our HLC WFC modeling for an as-built real system.

WFIRST Coronagraph Instrument (CGI) uses its Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to maintain the coronagraph contrast in presence of wavefront disturbances from the WFIRST observatory. The Occulting Mask Coronagraph (OMC) dynamic testbed is used to demonstrate LOWFS/C performance together with the coronagraphs. We have demonstrated that LOWFS/C can maintain coronagraph contrast to better than 10^-8 in presence of WFIRST-like LoS and low order WFE disturbances for both Hybrid Lyot Coronagraph (HLC) and Shaped Pupil Coronagraph (SPC) modes. However, in our previous tests the LoS disturbances simulated on the testbed were from the modeling of a single reaction wheel with a quasi-static wheel speed. In this paper we will describe the LOWFS/C LoS performance test in which the injected LoS disturbances are derived from all six reaction wheels on WFIRST, each with an independent varying wheel speed profile modeled for a typical coronagraph observational scenario. We will describe the LoS disturbances profile and testbed implementation approach. We will present the LOWFS/C LoS feedback and feed forward loops testbed performance under these realistic LoS disturbances in which we have demonstrated the LoS control that meets the CGI requirement.

A photon counting camera based on a modified Teledyne-e2v CCD201-20 electron multiplying CCD (EMCCD) is being developed for the NASA WFIRST coronagraph, an exoplanet imaging technology development of the Jet Propulsion Laboratory (Pasadena, CA). The coronagraph is designed to demonstrate technologies required to directly image planets around nearby stars, and to characterize their spectra. The planets are exceedingly faint, providing signals similar to the detector dark current, and require the use of photon counting detectors. Red sensitivity (600-980nm) is preferred to capture spectral features of interest. EMCCDs are baselined both as science and wavefront sensors in the coronagraph in order to simplify the system architecture. We are engaged in a technology development program with Teledyne-e2v to ruggedize the sensors for use in space. The modified detectors minimize the required number of charge transfers and the exposure of signal charge to trap defects in order to extend their lifetime in space. In this paper we will summarize our progress, program status, and plans for flight development.

The WFIRST Coronagraph Instrument (CGI) will image the environment close to stars at orders of magnitude higher sensitivity than current observatories. In addition to directly imaging giant exoplanets, WFIRST CGI has unprecedented sensitivity to scattered light from circumstellar dust. Most modeling has been confined to the dark-hole regime of the coronagraph (approximately 0.15 arcsec to 1 arcsec). This work uses publicly available field-dependent point spread functions to model an exozodiacal disk within the 0.15 arcsec inner working angle. For this simple Solar System-like test case, we find an approximately 25% increase in the transmitted exozodiacal flux due to light inside the inner working angle. We also describe plans to accelerate and extend this modeling to a wider range of geometries, and to quantify the impact on post-processing and source detection.

Starshades are a leading technology to enable the direct detection and spectroscopic characterization of Earth-like exoplanets. Starshade starlight suppression technology is being advanced through sub-scale starshade demonstrations at the Princeton Starshade Testbed and we present here the successful completion of a technology milestone focused on the demonstration of high contrast at flight-required levels. We demonstrate 10^-10 contrast at the inner working angle of a starshade with a flight-like Fresnel number at multiple wavelengths spanning a 10% bandpass. We show that while contrast at the inner working angle is limited by the presence of non-scalar diffraction as light propagates through narrow slits between the starshade petals, high contrast is still achieved over most of the image. Successful completion of this milestone verifies we can design a starshade capable of producing scientifically useful contrast levels.

We present an analysis of the Rayleigh scattering in the Princeton starshade testbed and show that it explains several notable features in the contrast images. The scattering is consistent with that expected due to air molecules and does not require airborne dust to explain. Rayleigh scattering limits the observable contrast at the ~ 1 × 10^-11 level at the inner working angle in the contrast images, but it limits the observable suppression at ~ 10^-9 level. We present a crude estimate of the level of scattering of starlight to be expected in a flight starshade due to zodiacal dust in the solar system and conclude that it is unlikely to be observable. We comment on whether Rayleigh scattering drives longer starshade testbeds to operate in vacuum.

One of the most promising mission concepts for imaging and characterizing Earth-like planets about other stars is a telescope/starshade system. But, in order to maximize the number of targets accessible for a given mission formation-keeping strategies are required. This paper details the design and implementation of a formation ying hardware-in-the-loop simulation in the existing Princeton Starshade Testbed to validate formation sensing and control algorithms while maintaining high contrast with a ight-like starshade. We present initial experimental results to help advance the starshade technology gap of formation sensing and control.

We have developed a suite of software forming an end-to-end starshade imaging tool that produces images of an arbitrary user-defined exoplanetary system and background as observed by a starshade and a telescope. The starshade imaging characteristics include both the diffraction from an ideal or perturbed starshade as well as solar glint from the starshade edges, the largest source of local instrument scatter. The telescope model assumes an ideal telescope with a user-defined obscured pupil (e.g. secondary obstruction and struts). It incorporates a vanilla detector model with read noise and dark current. Finally, the astrophysics scenario incorporates Keplerian orbits, phase angles, geometric albedo, different atmospheric scattering/absorption laws, any kind of host star (by default the user can choose among any of the +10,000 stars from ExoCat) and a large variety of extragalactic background fields (galaxies, Quasars). Exodust emission is accurate for a solar system and flexible for an arbitrary user-defined profile. As a result, it can virtually build a large variety of extra-solar systems with an arbitrary number of exoplanets of multiple types and any host star, adding an optional background field, to obtain a series of images throughout the proposed mission. Proper motion and parallax are also taken into account when background fields are added to the simulated images. There are default systems, like the Solar System at any distance from us. We have employed the tool to support WFIRST-S, HabEx, and other mission probe studies and ground telescope concepts.

This paper presents an overview of the work to date on the mechanical system for Starshade to TRL5 (S5) Technology Development Plan, with emphasis on the technical status compared to the upcoming technology milestones with an overview of how that work fits into the overall technology plan. The conclusion of the NASA trade study in 2018 for the starshade mechanical architecture resulted in a consolidated and focused approach, which was the baseline design used for the technology plan. Recent progress has included the production of multiple prototypes including a full-scale Petal Launch Restraint & Unfurl Subsystem prototype (14m tip to tip deployed), and has included demonstrations of the design from fully stowed to deployed. A10m (full-scale) inner disk subsystem including perimeter truss and optical shield was designed, analyzed, built and tested for deployment functionality and accuracy. Lastly, a 4m long × 1.5m wide (1/2 scale × 3/4 scale) petal prototype along with shape critical components of the perimeter truss have been built and tested for thermal stability. The culmination of this work, both in the design side and the prototype side, has led to greatly improved design fidelity, and most importantly, validation of the design against the performance requirements. This provides much greater confidence in the viability of the design, and much lower risk moving forward toward technology readiness level 5, and eventually a flight mission.

A starshade enables direct imaging of Earth-like exoplanets in the habitable zone of nearby stars by suppressing light from a target star so that orbiting planets are revealed. The perimeter of a starshade, known as the optical edge, has two critical functions. First, it must meet a precise in-plane profile specification to form a deep shadow in which the telescope is placed. Second, it must minimize reflected sunlight, as scattered sunlight significantly degrades the achievable contrast. Prior work on small scales and in a laboratory environment has shown that these requirements can be met using a chemically etched amorphous metal foil. This paper describes the next step of development, a first ever demonstration of assembled optical edge segments that meet both requirements simultaneously. The segments were constructed using space-compatible components and tested to relevant thermal and mechanical environments. A thorough assessment of edge performance, including in-plane profile, sunlight scatter and mechanical survivability was performed both before and after environmental testing. Furthermore, a custom scattered light testbed has been developed to quantify the magnitude of scattered sunlight over the entire length of the optical edge. The results of this study inform the future development of optical edge technology and pave the way towards eventual flight implementation.

The Remote Occulter (Orbiting Starshade) is a proposed 100-meter class starshade working with a ground-based telescope, designed for visible-band imaging and spectroscopy of temperate planets around sun-like stars. With advanced adaptive optics and the largest telescopes like the 39 m ELT, it would enable the study of planetary systems and a wide variety of exoplanets. In this paper, we describe the geometrical constraints and establish which parts of the sky are observable.

The Keck Planet Imager and Characterizer (KPIC) is an upgrade to the Keck II adaptive optics system enabling high contrast imaging and high-resolution spectroscopic characterization of giant exoplanets in the mid-infrared (2-5 microns). The KPIC instrument will be developed in phases. Phase I entails the installation of an infrared pyramid wavefront sensor (PyWFS) based on a fast, low-noise SAPHIRA IR-APD array. The ultra-sensitive infrared PyWFS will enable high contrast studies of infant exoplanets around cool, red, and/or obscured targets in star forming regions. In addition, the light downstream of the PyWFS will be coupled into an array of single-mode fibers with the aid of an active fiber injection unit (FIU). In turn, these fibers route light to Keck's high-resolution infrared spectrograph NIRSPEC, so that high dispersion coronagraphy (HDC) can be implemented for the first time. HDC optimally pairs high contrast imaging and high-resolution spectroscopy allowing detailed characterization of exoplanet atmospheres, including molecular composition, spin measurements, and Doppler imaging. We will provide an overview of the instrument, its science scope, and report on recent results from on-sky commissioning of Phase I. We will discuss plans for optimizing the instrument to seed designs for similar modes on extremely large telescopes.

The Keck Planet Imager and Characterizer comprises of a series of upgrades to the Keck II adaptive optics system and instrument suite to improve the direct imaging and high resolution spectroscopy capabilities of the facility instruments NIRC2 and NIRSPEC, respectively. Phase I of KPIC includes a NIR pyramid wavefront sensor and a Fiber Injection Unit (FIU) to feed NIRSPEC with a single mode fiber, which have already been installed and are currently undergoing commissioning. KPIC will enable High Dispersion Coronagraphy (HDC) of directly imaged exoplanets for the first time, providing potentially improved detection significance and spectral characterization capabilities compared to direct imaging. In favorable cases, Doppler imaging, spin measurements, and molecule mapping are also possible. This science goal drives the development of phase II of KPIC, which is scheduled to be deployed in early 2020. Phase II optimizes the system throughput and contrast using a variety of additional submodules, including a 952 element deformable mirror, phase induced amplitude apodization lenses, an atmospheric dispersion compensator, multiple coronagraphs, a Zernike wavefront sensor, and multiple science ports. A testbed is being built in the Exoplanet Technology Lab at Caltech to characterize and test the design of each of these submodules before KPIC phase II is deployed to Keck. This paper presents an overview of the design of phase II and report on results from laboratory testing.

The Keck Planet Imager and Characterizer (KPIC) is an upgrade to the Keck II adaptive optics system that includes an active fiber injection unit (FIU) for efficiently routing light from exoplanets to NIRSPEC, a high-resolution spectrograph. The second phase of this upgrade, beginning at the end of 2019, will add a suite of new coronagraph modes as well as a 1000-actuator deformable mirror. One of these modes, operating in the K-band (2.2µm), will be the first Vortex Fiber Nuller (VFN) to go on sky. Vortex Fiber Nulling is a new interferometric method for suppressing starlight in order to spectroscopically characterize exoplanets at angular separations that are inaccessible with conventional coronagraph systems. A monochromatic starlight suppression of 6x10^{-5} has already been demonstrated with a VFN in the lab, thereby exceeding our goal performance, and a polychromatic demonstration is underway. Here we describe the new KPIC coronagraph modes and present the expected performance of the VFN mode using realistic parameters determined from on-sky tests done during the KPIC commissioning. We will also present the latest experimental results of the system using a laboratory replica of the KPIC instrument.

The success of ground-based instruments for high contrast exoplanet imaging depends on the degree to which adaptive optics (AO) systems can mitigate atmospheric turbulence. While modern AO systems typically suffer from millisecond time lags between wavefront measurement and control, predictive wavefront control (pWFC) is a means of compensating for those time lags using previous wavefront measurements, thereby improving the raw contrast in the post-coronagraphic science focal plane. A method of predictive control based on Empirical Orthogonal Functions (EOF) has previously been proposed and demonstrated on Subaru/SCExAO. In this paper we present initial tests of this method for application to the near-infrared pyramid wavefront sensor (PYWFS) recently installed in the Keck II AO system. We demonstrate the expected root-mean-square (RMS) wavefront error and contrast benefits of pWFC based on simulations, applying pWFC to on-sky telemetry data saved during commissioning of the PYWFS. We discuss how the performance varies as different temporal and spatial scales are included in the computation of the predictive filter. We further describe the implementation of EOF pWFC within the PYWFS dedicated real-time controller (RTC), and, via daytime testing at the observatory, we demonstrate the performance of pWFC in real time when pre-computed phase screens are applied to the deformable mirror (DM).

We describe the current performance of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument on the Subaru telescope on Maunakea, Hawaii and present early science results for SCExAO coupled with the CHARIS integral field spectrograph. SCExAO now delivers H band Strehl ratios up to ~0.92, extreme AO corrections for optically faint stars, and planet-to-star contrasts rivaling that of GPI and SPHERE. CHARIS yield high signal-to-noise detections and 1.1—2.4 micron spectra of benchmark directly-imaged companions like HR 8799 cde and kappa And b that clarify their atmospheric properties. We show how spectra and astrometry for kappa And b lead to a reevaluation of this object's nature. Finally, we briefly describe plans for a SCExAO-focused direct imaging campaign to directly image and characterize young exoplanets, planet-forming disks, and (later) mature planets in reflected light.

The science promised by high-contrast imaging missions will result in great leaps in our understanding of exoplanetary and the detection and spectral characterization of Earth-like planets in the habitable zone. However, none of these missions can image multi-star systems with current technology except when the leak and glare of the companion star(s) is negligible or small enough to be removed by post-processing. Therefore, many systems with multiple stars (or optical multiples) are often excluded from target lists of such missions. Our solution to binary star suppression is a wavefront control algorithm called Multi-Star Wavefront Control (MSWC). In general, any region of interest where we wish to detect planets contains a mix of speckles from both stars, which are mutually incoherent. When MSWC is used It is possible to null speckles from both stars if the region of interest is appropriately chosen, and non-redundant modes of the Deformable Mirror are used. Feasibility of MSWC was demonstrated in computer simulations and at the Ames Coronagraph Experiment Experiment laboratory. In this paper, we report the demonstration of MSWC using the Subaru Coronagraph Extreme Adaptive Optics (SCExAO) as part of our technology development effort. Our goal is to show that MSWC can achieve an order of magnitude better contrast on binary stars than conventional (i.e., single-star) techniques on binaries. Demonstrating this technique on SCExAO will validate MSWC on a real system (with a calibration source). Thus, proving that the technique can be applied on deployed instrumentation without major modifications.

The EXOplanet high resolution SPECtrograph (EXOhSPEC) instrument is an echelle spectrograph dedicated to the detection of exoplanets by using the radial velocity method using 2m class telescopes. This spectrograph is specified to provide spectra with a spectral resolution R < 70, 000 over the spectral range from 400 to 700 nm and to reach a shortterm radial velocity precision of 3 m/s. To achieve this the separation between two adjacent spectral orders is specified to be greater than 30 pixels and to enable a wide range of targets the throughput of the instrument is specified to be higher than 4%. We present the results of the optimization of the spectrograph collimator performed and initial tests of its optical performance. First, we consider the spectrograph design and we estimate its theoretical performance. We show that the theoretical image quality is close to the diffraction limit. Second, we describe the method used to perform the tolerancing analyzes using ZEMAX software to estimate the optical performance of the instrument after manufacturing, assembly and alignment. We present the results of the performance budget and we show that the estimated image quality performance of EXOhSPEC are in line with the specifications. Third, we present the results of the stray light analysis and we show that the minimum ratio between the scientific signal and the stray light halo signal is higher than 1,000. Finally, we provide a status on the progress of the EXOhSPEC project and we show the first results obtained with a preliminary version of the prototype.

We present a numerical study of the diffraction effects and controllability of telescope assembly polarization aberrations on apodized pupil Lyot coronagraph (APLC) and vector vortex coronagraph (VVC) designs for the LUVOIR-A and LUVOIR-B mission concepts. We also examine interactions between polarization aberrations and vector vortex masks, which induce a geometrical helical phase to achieve deep nulling of incident starlight.

Non Common Path Aberrations (NCPA) are often considered as a critical issue in Adaptive Optics (AO) systems, since they introduce bias errors between real wavefronts propagating to the science detectors and those measured by the Wavefront Sensor (WFS). This is especially true when the AO system is coupled to a coronagraph instrument intended for the discovery and characterization of extra-solar planets, because useful planet signals could be mistaken with residual speckles generated by NCPA. Therefore, compensating for those errors is of prime importance and is already the scope of a few theoretical studies and experimental validations on-sky. This communication presents the conceptual optical design of an interferometric arrangement suitable to accurate NCPA calibration, based on two WFS cooperating in real-time. The concept is applicable to both classical imaging and spectroscopy assisted by AO, and to high-contrast coronagraphs searching for habitable extra-solar planets. Practical aspects are discussed, such as the choice of WFS and coronagraph types, or specific requirements on additional hardware components, e.g. dichroic beamsplitters.

We discuss the use of parametric phase-diverse phase retrieval to characterize and optimize the transmitted wavefront of a high-contrast apodized pupil coronagraph with and without an apodizer. We apply our method to correct the transmitted wavefront of the HiCAT (High contrast imager for Complex Aperture Telescopes) coronagraphic testbed. This correction requires a series of calibration steps, which we describe. The correction improves the system wavefront from 16 nm RMS to 3.0 nm RMS for the case where a uniform circular aperture is in place. We further measure the wavefront with the apodizer in place to be 11.7 nm RMS. Improvement to the apodized pupil phase retrieval process is necessary before a correction based on this measurement can be applied.

The contrast/bandwidth performance for current implementations of the Vector Vortex Coronagraph (VVC) is degraded by a leakage term that emerges when the optic does not exhibit a retardance of exactly half-wave. We present a novel implementation for the VVC that significantly rejects the polarization leakage term through diffraction. The optic consists of multiple separate layers of patterned liquid crystals, for which each extra layer adds two orders of magnitude of leakage rejection. The first layer combines a vortex pattern and a polarization grating into a so-called forked grating that splits the circular polarization states. Consecutive polarization gratings effectively cancel the first grating with full diffraction direction efficiency, resulting in a regular vortex phase with minimized leakage of the non-coronagraphic PSF. We present the designs and performance of double-grating VVC for the ground-based instruments VLT/SPHERE and Subaru/SCExAO, that instantaneously cover 1-2.5 um. In addition, we introduce the triple-grating VVC that fulfills the stringent requirements for technology demonstration towards high-contrast imaging at ~1E-10 levels with future space telescopes like the HabEx and LUVOIR mission concepts.

The Phase-Induced Amplitude Apodization (PIAA) technique represents a family of high performance coronagraphs with high throughput, aggressive inner working angles (IWAs), and compatible with obstructed apertures. This is particularly important because Large UV / Optical/ Infrared (LUVOIR) and HabEx B concepts currently considered for the 2020 decadal survey are based on obstructed and/or segmented apertures. Higher throughputs and IWAs enable significant science gains, or significant savings in size and cost of a mission without reducing science. Historically, however, PIAA-based designs on segmented apertures (PIAACMC) were also sensitive to low order aberrations such as tip/tilt jitter, as well as large stellar angular sizes. In this paper, we show a classic PIAA design for the segmented aperture of LUVOIR B that features high tolerance to low-order aberrations. It can gain arbitrarily good sensitivity to low order aberrations at the expense of IWA, by varying the size of the focal plane mask. Missions can either commit to a single mask, or have several masks, selecting the one best suited for each target’s stellar size, which can further increase science yield. We find that in order to maintain 1e-10 contrast for stellar diameters of 0.1 l/D, the IWA needs to be enlarged to 3 l/D. Finally, we show that in theory, it is possible for coronagraphs to have much better inner working angles while being tolerant to 0.1 l/D diameter stars, so there is still a lot of opportunity to improve the science yield of a given mission by developing even better coronagraphs.

Vortex fiber nulling (VFN) is a method that may enable the detection and characterization of exoplanets at small angular separations (0.5-2 λ/D) with ground- and space-based telescopes. Since the field of view is within the inner working angle of most coronagraphs, nulling accesses non-transiting planets that are otherwise too close to their star for spectral characterization by other means, thereby significantly increasing the number of known exoplanets available for direct spectroscopy in the near-infrared. Furthermore, VFN targets planets on closer-in orbits which tend to have more favorable planet-to-star flux ratios in reflected light. Here, we present the theory and applications of VFN, show that the optical performance is approximately equivalent for a variety of implementations and aperture shapes, and discuss the trade-offs between throughput and engineering requirements using numerical simulations. We compare vector and scalar approaches and, finally, show that beam shaping optics may be used to significantly improve the throughput for planet light. Based on theoretical performance, we estimate the number of known planets and theoretical exoEarths accessible with a VFN instrument linked to a high-resolution spectrograph on the future Thirty Meter Telescope.

Direct imaging of exo-Earths and search for life is one of the most exciting and challenging objectives for future space observatories. Segmented apertures in space will be required to reach the needed large diameters beyond the capabilities of current or planned launch vehicles. These apertures present additional challenges for high-contrast coronagraphy, not only in terms of static phasing but also in terms of their stability. The Pair-based Analytical model for Segmented Telescope Imaging from Space (PASTIS) was developed to model the effects of segment-level optical aberrations on the final image contrast. In this paper, we extend the original PASTIS propagation model from a purely analytical to a semi-analytical method, in which we substitute the use of analytical images with numerically simulated images. The inversion of this model yields a set of orthonormal modes that can be used to determine segment-level wavefront tolerances. We present results in the case of segment-level piston error applied to the baseline coronagraph design of LUVOIR A, with minimum and maximum wavefront error constraint between 56 pm and 290 pm per segment. The analysis is readily generalizable to other segment-level aberrations modes, and can also be expanded to establish stability tolerances for these missions.

The speckles pattern in the imaging plane of a high contrast coronagraph is highly sensitive to perturbations of the wavefront in the pupil plane. As these wavefront errors vary in time, they may significantly increase the intensity of the speckles and thus impose overly stringent constraints on wavefront stability. A recently proposed solution is to perform a recursive estimation of the speckles field and reduce its intensity via Electric Field Conjunction (EFC), both done while continuously observing the target star. For accuracy purposes, this estimation procedure requires introducing phase diversity in the imaging plane which is done via dithering the deformable mirror controls around their optimal EFC value. The faster the speckles drift, the more dithering is necessary for the controller to remain stable, hence more starlight is introduced into the dark hole and the post processing factor (the dimmest exoplanet that can be observed) decreases. Using a model of the Wide- Field Infra-Red Survey Telescope (WFIRST) Coronagraph Instrument (CGI), we illustrate the effects of drift magnitude on the best contrast achieved by the dark hole maintenance scheme. We then consider the resulting post-processing factors corresponding to a posteriori estimates of the intensity of sources incoherent with the star.

Coronagraphic instruments will enable direct imaging of dim planetary companions around nearby stars. The majority of nearby FGK stars are located in multi-star systems, including the Alpha Centauri stars, which may represent the best quality targets available for spectroscopic characterization due to their proximity and brightness. However, a binary system exhibits additional leakage from the off-axis companion star that may be brighter than the target exoplanet. Multi-Star Wavefront Control (MSWC) is a wavefront-control technique that allows simultaneous suppression of starlight of both stars in a binary system. MSWC would thus enable direct imaging of circumstellar planets in binary star systems such as Alpha Centauri. MSWC is compatible with a wide suite of planned coronagraphic instruments for future space missions. As part of the technology demonstration efforts for MSWC, the first milestone results are presented here demonstrating (via computer simulations), high-contrast imaging capabilities of multi-star systems for several instruments including: [1] the upcoming WFIRST and its CGI demonstrator, [2] the HABitable Worlds EXplorer (Habex) mission concept, [3] the segmented Large UV/Optical/IR (LUVOIR) mission concept, and [4] a small-aperture Alpha Centauri direct-imager mission concept. For each of these missions, a baseline coronagraph option planned for the mission will be adopted and instrument baseline performance will be compared for single-star wavefront control.

Using single-mode fibers (SMFs) in the image plane of coronagraphs allows access to a new wavefront control regime. By using deformable mirrors to create a mismatch between the incoming starlight and the fiber mode, SMFs can serve as integral parts of the light suppression ability of the coronagraph. Previous promising simulation results show increased spectral bandwidth and throughput when using SMFs in a multi-object role, and previous laboratory results have shown increased light suppression using a single SMF. We present an update on efforts to combine a multi-core SMF with a high-resolution spectrograph on the High Contrast Testbed for Segmented Telescopes (HCST) at Caltech. We present our planned experimental design, as well as simulations of expected performance when controlling multiple fiber cores on HCST. We will test the potential increase in spectral bandpass and throughput resulting from the switch to SMFs, as well as the stability of the wavefront control solution.

Accurate characterization of exoplanet orbits requires multiple observations made over one or more orbital periods. We use a rejection sampling algorithm to study how uncertainty in the observation data manifests in the computed orbital parameters and how this uncertainty depends on the number and spacing of observations. We find that 3 observations equally spaced over at least one half of an orbital period robustly reduces the uncertainty in the semi-major axis and eccentricity to below 10%. We also study modifications of this revisit strategy in the presence of a central obscuration and show how null observations may still be leveraged to constrain a detected exoplanets orbital parameters. Finally, we suggest a method for incorporating photometric data into the rejection sampling framework to break degeneracy in the orbit fitting procedure and further constrain the orbital parameters.

The Wide Field Infrared Survey Telescope (WFIRST) Coronagraphic Instrument (CGI) technology demonstration and potential science mission, as well as mission concepts with exoplanet imaging capabilities such as HabEx and LUVOIR, all require the identification of the best targets for exoplanet observations. To date, the focus has been primarily on two classes of targets: those with known exoplanets discovered indirectly that may be observable by these imaging missions, and those targets with no known planets that have high completeness values (probabilities of planet detections) under some assumptions of the instrument performance and the overall population of exoplanets. A third class of target, however, has received much less scrutiny: stars with known exoplanets that could not possibly be directly imaged due to the size of their orbits. These are planets that would be guaranteed to spend all of their time inside the inner working angles or outside the outer working angles of all currently proposed coronagraphs. However, these systems could potentially harbor additional planets, either exterior to or interior to the currently known planets, but not yet detectable by indirect means. Here, we discuss how to identify systems from all three categories that would be good targets for WFIRST and other, future, space-based imagers. We present a method for assessing the utility of these targets based on an exploration of the available dynamical phase space of the systems that would result in long-term stable orbits for both the currently known and the potentially discoverable companions, and show how it augments existing methods for assessing target completeness and utility.

Vortex coronagraphs are an attractive solution for imaging exoplanets with future space telescopes due to their relatively high throughput, large spectral bandwidth, and low sensitivity to low-order aberrations compared to other coronagraphs with similar inner working angles. Most of the vortex coronagraph mask development for space applications has focused on generating a polychromatic, vectorial, optical vortex using multiple layers of liquid crystal polymers. While this approach has been the most successful thus far, current fabrication processes achieve retardance errors of 0.1-1.0°, which causes a nonnegligible fraction of the starlight to leak through the coronagraph. Circular polarizers are typically used to reject the stellar leakage reducing the throughput by a factor of two. Vector vortex masks also complicate wavefront control because they imprint conjugated phase ramps on the orthogonal circular polarization components, which may need to be split in order to properly sense and suppress the starlight. Scalar vortex masks can potentially circumvent these limitations by applying the same phase shift to all incident light regardless of the polarization state and thus have the potential to significantly improve the performance of vortex coronagraphs. We present scalar vortex coronagraph designs that make use of focal plane masks with multiple layers of dielectrics that (a) produce phase patterns that are relatively friendly to standard manufacturing processes and (b) achieve sufficient broadband starlight suppression, in theory, for imaging Earth-like planets with future space telescopes.

High contrast imaging and characterization of faint exoplanets require a coronagraph instrument to efficiently suppress the host star light to 10^-9 level contrast over a broad spectral bandwidth. The NASA WFIRST mission plan includes a coronagraph instrument to demonstrate the technology needed to image and characterize exoplanets. Lyot coronagraph masks designed to serve at the focal plane followed by a Lyot stop will be key elements in the WFIRST coronagraph and in future advanced missions such as LUVOIR (Bolcar (2019) and HabEx (Morgan 2019, Martin 2019)). Shaped pupil masks designed to work in reflective geometry are also employed in the WFIRST Coronagraph. High-contrast performance reaching much better than 10^-9 contrast requires very tight design, fabrication tolerances, and material properties to meet a wide range of specifications, including precise shapes, micron-scale island features, ultra-low reflectivity regions, uniformity, wavefront quality, etc. In this paper, we present all the critical analytical and measured properties of materials and designs in relation to the results from our coronagraph testbeds.

The Subaru telescope detects exoplanets at contrasts of 1 × 10^-5 by using a shaped pupil coronagraph. The shaped pupil is a binary mask designed to alter the propagation of light to the image plane in a way that produces dark holes (also called "discovery regions") where off-axis point sources can be detected more easily. Our objective is to decrease the inner working angle (IWA) of the discovery regions to allow for detection of Earth-like planets found closer to the target star. The current Subaru shaped pupil has an IWA of 3.5 λ/D and an outer working angle (OWA) of 16 λ/D. These characteristics of the IWA limit the detection of planets close to the star and the low transmission level of the shaped pupil potentially intercepts the transmission of o_-axis point sources. Here we present a new pupil design that attains a smaller IWA and achieves a transmission of greater than 50%, while maintaining the current contrast level. The tradeoff is a smaller OWA, which allows for less discovery space at the outer regions of the image plane. We also explore the potential benefits of setting the desired level of transmission and maximizing the contrast, as opposed to the current method of fixing the contrast and maximizing the transmission.

Exoplanet detection by direct imaging is difficult because the target planets are tens of milliarcseconds away from their host star and many orders of magnitude dimmer, up to 1e10 for Earth-like planets in the habitable zone. An important approach to obtaining that high contrast in a space telescope is via a starshade to suppress the light from the parent star, making the direct imaging possible. Even after suppressing the starlight, the exoplanet signals are still weak. A photon-counting (PC) Electron Multiplying Charged Coupled Device(EMCCD) reduces the noise level and enables the detection of exoplanets. We present here a signal detection and estimation technique working directly with PC images. The method is based on the generalized maximum likelihood ratio test (GLRT) and uses a binomial distribution between PC images. The method can be applied online, so we can stop taking images as soon as we have enough confidence for the lack of or existence of planets. Thus, the observation time is efficiently used.

A sunflower-like starshade positioned between an exoplanet host star and a telescope forms a deep shadow at the telescope enabling the faint exoplanet to be viewed without being overwhelmed by veiling glare from the star. The starshade perimeter has hundreds of meters of sharp edge that are directly exposed to sunlight. The sunlight diffracts and reflects from the edge resulting in a glint pattern that can be brighter than the exoplanet. We have developed models of the edge glint to explain laboratory measurements, to guide the development of edges with minimum glint, and to determine the fundamental glint floor which is set by diffraction. The models include finite difference time domain calculations, Sommerfeld's half-plane diffraction expressions, and a micro-facet scattering model. Models successfully reproduce the features and magnitude of the measured polarization-dependent scatter and show that measured edges are performing near the theoretical limit.

High-resolution spectrometers have proven to be an important tool for astronomical observations and continue to have an ever expanding set of applications, such as high resolution IFS (Integral Field Spectroscopy). With this in mind, we present an alternative approach to the design and construction of Echelle type spectrometers. The usual approach is to drive high resolving power through the use of large gratings and long focal length collimators, leading to great production costs in the order of $1,000,000. Our compact, proof-of-concept prototype, via the coupling of adaptive optics, achieves comparable performance and resolution; with a theoretical resolving power R<80,000 in the Vis-NIR regime (500nm- 1μm) at a cost <$10,000. This is attained through the use of COTS (Commercially-Off-The-Shelf) and economically designed components. The overall device footprint is compact, measuring the size of a ‘shoe-box’, approximately 30cm×15cm. The spectrometer prototype is fibre-fed with a single 10μm fibre and follows a double-pass design - applying a custom designed, 108.24mm focal length, collimating and re-focussing lens. The system follows an Echelle type design with high resolution achieved through the use of a compact R4 diffraction grating and a prism as the cross-disperser.

FOCES is a highly stabilized high-resolution optical Échelle spectrograph operated with the 2m telescope at the Wendelstein Observatory. After an extensive temperature- and pressure-stabilization upgrade, reaching the m/s-level, we now focus on the wavelength calibration process. Due to our latest improvements, we are able to perform simultaneous wavelength calibration using our new 4-_ber-slit assembly. This allows us to couple the spectrum of a star and light from a ThAr/UNe hollow cathode lamp or our frequency comb_ at the same time into the spectrograph. We present the design, production process and performance of this new multi-fiber assembly and also evaluate the stability as a test for the upcoming high precision radial velocity measurements in search of exoplanets.

We introduce a notional nulling interferometer for extinction of glare from single star exoplanetary systems. The principle of double dispersion telescopy correlates an incident angular position with a unique wavelength. In such telescopes, a secondary spectrograph is used to disambiguate overlapping wavelengths from the primary disperser. A single rejection band can be created in the secondary spectrograph based on the resulting wavelength modulation. Two optical paths are directed from the slit situated between the primary and secondary dispersers. Angles of incidence and path lengths are slightly offset between the pair of post-slit wave trains. By this configuration, a half wave path difference is established at the position and diameter of the host star, causing phase cancellation at a unique spectral band. Having a single rejection band avoids repetitive banding endemic to conventional interferometric telescopy. There is a tradeoff with chromatic aberration in the images of the exoplanets.

The Planetary Imaging Concept Testbed Using a Recoverable Experiment - Coronagraph (PICTURE-C) is a direct imaging experiment designed to observe exozodiacal dust and debris disks that orbit nearby stars from a high-altitude balloon platform. The experiment consists of a vector vortex coronagraph and a multi stage adaptive optics system with multiple wavefront sensors and two deformable mirrors. This paper details the hardware and software implementation of one of the DM interfaces used in the PICTURE-C low-order wavefront control system. We discuss the algorithm used to drive a commercial o_-the-shelf DM with an actuation resolution of 14-bits to meet the PICTURE-C requirement of 16-bits. The algorithm utilizes fast temporal dithering in the form of pulse density modulation to reduce the quantization error of the DM actuation. The described DM control mechanism can operate at a framerate of ~500 Hz with an equivalent actuation resolution of 16-bits with minimal computational load on the deployed processor.

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. PICTURE-C employs both image-plane wavefront sensing for high-order wave- front control and a reflective Lyot-stop sensor for low-order wavefront control. Since both of these systems lie downstream from the coronagraph's deformable mirror, and since both must run simultaneously, they must be calibrated as to not interfere with each other. The deformable mirror probe patterns required for image-plane sensing appear as wavefront errors to the low-order sensor. This paper presents simulations of low and high-order wavefront sensing for PICTURE-C and calibration techniques for decoupling the two sensors.

The Large Binocular Telescope Interferometer (LBTI) has the longest baseline in the world|22.7 m|for performing astronomical interferometry in Fizeau mode, which involves beam combination in a focal plane and preserves a wide field-of-view. LBTI can operate in this mode at wavelengths of 1.5-5 and 8-12 μm, making it a unique platform for carrying out high-resolution imaging of circumstellar disks, and possibly searches for planets, in the thermal infrared. Over the past five years, LBTI has carried out a considerable number of interferometric observations by combining the beams near a pupil plane to carry out nulling interferometry. This mode is useful for measuring small luminosity level offsets, such as those of exozodiacal dust disks. The Fizeau mode, by contrast, is more useful for generating an image of the target because it has more uv plane coverage. However, the Fizeau mode is still in an ongoing process of commissioning. Sensitive Fizeau observations require active phase control, increased automation, and the removal of non-common-path (NCP) differential aberrations. These maximize the fringe contrast, enable longer integrations, and reduce time overheads. We are in the process of writing a correction loop to remove NCP aberrations, and have carried out tests on old and synthetic data. We have also carried out on-sky Fizeau engineering tests in 2018B and 2019A. In this article, we share lessons learned and strategies developed as a result of these tests.

Direct imaging of an Earth-like exoplanet requires starlight suppression with a contrast ratio on the order of 1×10^-10 at small angular separations of 100 milliarcseconds or less in visible light. To aid the technology development to reach this capability and enable future exoplanet missions, we built a high contrast coronagraph testbed, titled the Decadal Survey Testbed (DST). As of early 2019, the testbed has repeatedly demonstrated a monochromatic contrast floor about 1×10^-10, and broadband performance at 550 nm with 10% color band- width <4×10^-10 . The testbed has also demonstrated open-loop contrast drift rates of around 10^-10/hour, temperature drift stabilities of <10 milliKelvins/day, passive pointing stability of around 0.1 λ/D per day on the occulting mask, and rms pointing jitter around 0.005 λ/D. This paper focusses primarily on the testbed hardware description, and a companion paper by Seo et al. details the experimental results.

Direct imaging of an Earth-like exoplanet requires starlight suppression with a contrast ratio on the order of 1 ♦ 10^-10 at small angular separations of 100 milliarcseconds or less in visible light with more than 50 nm bandwidth. To our knowledge, the technology needed to achieve the contrast and stability has not been demonstrated as of January 2019. The science requirements for near future NASA missions such as James Webb Space Telescope’s (JWST) Near Infrared Camera (NIRCam) coronagraph and Wide Field Infrared Space Telescope (WFIRST) Coronagraph Instrument (CGI) are at least 10 times short. To investigate and guide the technology to reach this capability, we built a high contrast coronagraph testbed at NASA’s Jet Propulsion Laboratory (JPL). Titled the Decadal Survey Testbed (DST), state-of-art testbed is based on the accumulated experience of JPL’s High Contrast Imaging Testbed (HCIT) team. Currently, the DST hosts a Hybrid Lyot Coronagraph (HLC) with an unobscured, circular pupil. The DST also has two deformable mirrors and is equipped with the Low Order Wavefront Sensing and Control (LOWFS/C) subsystem to sense and correct the dynamic wavefront disturbances. In this paper, we present up-to-date progress of the testbed demonstration. As of January 2019, we repeatedly obtain convergence below 4 × 10^-10 mean contrast with 10% broadband light centered at 550 nm in a 360 degrees dark hole with a working angle between 3 λ/D and 9 λ/D. We show the key elements used in the testbed and the performance results with associated analysis.

The High-Contrast Spectroscopy Testbed for Segmented Telescopes (HCST) in the Exoplanet Technology Laboratory (ET Lab) at Caltech is designed to test the technologies that will enable direct imaging and characterization of exoplanets with future segmented ground- and space-based telescopes. Wavefront sensing and control has been successfully implemented with electric field conjugation (EFC) using the FALCO Matlab package, yielding a baseline raw contrast of 1×10^-8 in narrowband light with a Vector Vortex Coronagraph over a clear aperture. Here we report on progress towards our next HCST milestones: 1- Demonstration of 10^-8 raw contrast levels in broadband light with the apodized vortex coronagraph using a LUVOIR B-like segmented aperture. 2- Integration of a fiber injection unit (FIU) and corresponding wavefront control algorithm to achieve 10^-8 raw contrast in broadband light through a single mode fiber enabling high dispersion coronagraphy.

High dispersion coronagraphy (HDC) is a technique that combines high contrast imaging techniques with high spectral resolution spectroscopy to directly characterize exoplanets and provide key information such as chemical composition, temperature, and rotational velocity. A consequence of adaptive optics systems used in direct imaging is the formation of residual bright spots of star lights, called speckles, in the final image. Due to the large difference in brightness between host stars and their planets, these speckles can easily obscure potential exoplanets. In a previous demonstration, it was shown that using monochromatic light and a fiber injection unit (FIU), simulated exoplanet light can be directed to a high-resolution spectrograph. The method had speckle suppression that exceeding conventional image-based speckle nulling. With a previous Kalman filter estimator implementation, we found that with the implementation of the algorithm, speckle suppression was even more stable and outperformed traditional speckle nulling. In this update to the estimator, progress has been made in terms of a new filter design, and better estimates of the physical parameters in the laboratory, resulting in a higher speckle nulling performance.

The goal of the High-contrast imager for Complex Aperture Telescopes (HiCAT) testbed is to demonstrate coronagraphic starlight suppression solutions for future segmented aperture space telescopes such as the Large UV, Optical, IR telescope (LUVOIR) mission concept being studied by NASA. The testbed design has the flexibility to enable studies with increasing complexity for telescope aperture geometries starting with off-axis telescopes, then on-axis telescopes with central obstruction and support structures. The testbed implements the Apodized Pupil Lyot Coronagraph (APLC) optimized for the HiCAT aperture, which is similar to one of the possible geometries considered for LUVOIR. Wavefront can be controlled using continuous deformable mirrors, and wavefront sensing is performed using the imaging camera, or a dedicated phase retrieval camera, and also in a low-order wavefront sensing arm. We present a progress update of the testbed in particular results using two deformable mirror control to produce high-contrast dark zone, and preliminary results using the testbed’s low order Zernike wavefront sensor.

Coronagraph-equipped direct imaging missions need an active wavefront control system to cancel out the optical aberrations that degrade the performance of the coronagraphs. A fast steering mirror is used to control Line-of- Sight (LoS) pointing error caused by the telescope jitter. In addition to controlling other low-order aberrations such as astigmatism and coma, high stroke, high actuator density deformable mirrors (DMs) are also used to control the electric field at the required high spatial frequencies. We are designing a testbed to verify a different deformable architecture, where the powered optic in the optical train are controllable and have lower actuator count compared to the existing DMs with nominal surfaces. This simplifies the packaging issue for space missions and reduces both cost and risk of having the entire coronagraph instrument's performance depending on one or two high-actuator count DMs. The testbed would also be capable of testing different low-order wavefront sensing algorithms, which focuses in the near-term on a new adaptive Kalman filtering and gradient decent method to estimate the harmonic LoS errors that affect space telescopes. In the long run, we would test different machine learning techniques to estimate low-order aberrations and non-linear algorithms for digging the region of high contrast called the dark holes (DH).

Imaging rocky planets in reflected light, a key focus of future NASA missions and ELTs, requires advanced wavefront control to maintain a deep, temporally correlated null of stellar halo at just several diffraction beam widths. We discuss development of Linear Dark Field Control (LDFC) to achieve this aim. We describe efforts to test spatial LDFC in a laboratory setting for the first time, using the Ames Coronagraph Experiment (ACE) testbed. Our preliminary results indicate that spatial LDFC is a promising method focal-plane wavefront control method capable of maintaining a static dark hole, at least at contrasts relevant for imaging mature planets with 30m-class telescopes.

This PDF contains the front matter associated with SPIE Proceedings Volume 11117, including the title page, copyright information, table of contents, and author and conference committee lists.