Real-time control (RTC) is pivotal for any Adaptive Optics (AO) system, including high-contrast imaging of exoplanets and circumstellar environments. It is the brain of the AO system, and what wavefront sensing and control (WFS&C) techniques need to work with to achieve unprecedented image quality and contrast, ultimately advancing our understanding of exoplanetary systems in the context of high contrast imaging (HCI). Developing WFS&C algorithms first happens in simulation or a lab before deployment on-sky. The transition to on-sky testing is often challenging due to the different RTCs used. Sharing common RTC standards across labs and telescope instruments would considerably simplify this process. A data architecture based on the interprocess communication method known as shared memory is ideally suited for this purpose. The CACAO package, an example of RTC based on shared memory, was initially developed for the Subaru- SCExAO instrument and now deployed on several benches and instruments. This proceeding discusses the challenges, requirements, implementation strategies, and performance evaluations associated with integrating a shared memory-based RTC. The Santa Cruz Extreme AO Laboratory (SEAL) bench is a platform for WFS&C development for large groundbased segmented telescopes. Currently, SEAL offers the user a non-real-time version of CACAO, a shared-memory based RTC package initially developed for the Subaru-SCExAO instrument, and now deployed on several benches and instruments. We show here the example of the SEAL RTC upgrade as a precursor to both RTC upgrade at the 3-m Shane telescopes at Lick Observatory (Shane-AO) and a future development platform for the Keck II AO. This paper is aimed at specialists in AO, astronomers, and WFS&C scientists seeking a deeper introduction to the world of RTCs.
We describe the motivation, design, and early results for our 42-night, 125 star Subaru/SCExAO direct imaging survey for planets around accelerating stars. Unlike prior large surveys, ours focuses only on stars showing evidence for an astrometric acceleration plausibly due to the dynamical pull of an unseen planet or brown dwarf. Our program is motivated by results from a recent pilot program that found the first planet jointly discovered from direct imaging and astrometry and resulted in a planet and brown dwarf discovery rate substantially higher than previous unbiased surveys like GPIES. The first preliminary results from our program reveal multiple new companions; discovered planets and brown dwarfs can be further characterized with follow-up data, including higher-resolution spectra. Finally, we describe the critical role this program plays in supporting the Roman Space Telescope Coronagraphic Instrument, providing a currently-missing list of targets suitable for the CGI technological demonstration without which the CGI tech demo risks failure.
The Compute and Control for Adaptive Optics (CACAO) is a free and open-source real-time library for adaptive optics (AO), initially developed for the operation of the 1200+ mode AO loop of Subaru/SCExAO. The scope has expanded since then, through refactorings, the addition of numerous features (predictive control, machine learning), and a substantial improvement of our understanding and configuration of the underlying real-time Linux distribution. We now witness the adoption of the package at multiple facilities, using a variety of cameras and WFSs: non-linear curvature, Shack-Hartmann, Photonic lanterns, and of course the pyWFS. At Subaru, CACAO is the core of the AO3K RTC, which supports legacy NGS and LGS mode, as well as the new high-order wavefront sensors coupled to an ALPAO 3224 deformable mirror. We present developments in algorithms -- bindings for machine learning algorithms, real-time configuration tools -- and user interface tools added in the past few years. We show performance benchmarks on the SCExAO and AO3K systems. We present our future plans to affirm CACAO as the go-to free, open-source RTC toolkit for real-time pipelines in the academic world.
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 introduce here the upgrade concept of the algorithm. 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.
We describe the design and initial results from a visible-light Lyot coronagraph for SCExAO/VAMPIRES. The coronagraph is comprised of four hard-edged, partially transmissive focal plane masks with inner working angles of 36 mas, 55 mas, 92 mas and 129 mas, respectively. The Lyot stop is a reflective, undersized design with a geometric throughput of 65.7%. Our preliminary on-sky contrast is 10−2 at 0.1 ′′ to 10−4 at 0.75′′ for all mask sizes. The coronagraph was deployed in early 2022 and is available for open use.
FIRST is a post Extreme Adaptive-Optics (ExAO) spectro-interferometer based on pupil remapping using single-mode fibers. Installed on the SCExAO platform at the Subaru Telescope, it operates in the Visible (600-800nm, R 400) and demonstrated companion detection below the telescope diffraction limit. As an interferometric device, FIRST is sensitive to phasing problems in the telescope pupil. This is particularly interesting to measure discontinuous aberrations, invisible to the ExAO sensors. Recent developments aimed to measure upstream aberrations directly from the same interferometric signal used for scientific data analysis. A key limitation to this new capability is the fiber thermal and mechanical instabilities, inducing up to 1 micron drift over a few seconds. We propose to use a metrology laser source, allowing to discriminate FIRST instrumental effects from all the upstream aberrations. We present the integration of this setup and the on-sky demonstration of the method.
Pupil fragmentation can result either from spider shadow or segmented primary mirrors. In both cases, differential low order aberrations (piston, tip or tilt) between the fragments lead to degrading high contrast instrument performance, since current Extreme Adaptive Optics sensors cannot properly sense them. Convinced that Focal Plane Wavefront Sensing is one great solution to deal with pupil phase discontinuities, we have been testing the Linearized Analytical Phase Diversity (LAPD) algorithm on SCExAO at the Subaru Telescope. This talk will recall advantages of LAPD in terms of capture range and speed. We will present lab demonstrations of LAPD both for Island Effect correction and segment cophasing on two different testbeds. Results of lambda/75 RMS cophasing error will be presented as a stepping stone for TMT cophasing. Lastly, we will present the first on-sky demonstration of LAPD on the Subaru Telescope.
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.
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.
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.
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.
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.
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.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) serves both a science instrument in operation, and a prototyping platform for integrating and validating advanced wavefront control techniques. It provides a modular hardware and software environment optimized for flexible prototyping, reducing the time from concept formulation to on-sky operation and validation. This approach also enables external research group to deploy and test new hardware and algorithms. The hardware architecture allows for multiple subsystems to run concurrently, sharing starlight by means of dichroics. The multiplexing lends itself to running parallel experiments simultaneously, and developing sensor fusion approaches for increased wavefront sensing sensitivity and reliability. Thanks to a modular realtime control software architecture designed around the CACAO package, users can deploy WFS/C routines with full low-latency access to all cameras data streams. Algorithms can easily be shared with other cacao-based AO systems at Magellan (MagAO-X) and Keck. We highlight recent achievements and ongoing activities that are particularly relevant to the development of high contrast imaging instruments for future large ground-based telescopes (ELT, TMT, GMT) and space telescopes (HabEx, LUVOIR). These include predictive control and sensor fusion, PSF reconstruction from AO telemetry, integrated coronagraph/WFS development, focal plane speckle control with photon counting MKIDS camera, and fiber interferometry. We also describe upcoming upgrades to the WFS/C architecture: a new 64x64 actuator first stage DM, deployment of a beam switcher for concurrent operation of SCExAO with other science instruments, and the ULTIMATE upgrade including deployment of multiple LGS WFSs and an adaptive secondary mirror.
Focal plane wavefront sensing is an elegant solution for wavefront sensing since near-focal images of any source taken by a detector show distortions in the presence of aberrations. Non-Common Path Aberrations and the Low Wind Effect both have the ability to limit the achievable contrast of the finest coronagraphs coupled with the best extreme adaptive optics systems. To correct for these aberrations, the Subaru Coronagraphic Extreme Adaptive Optics instrument hosts many focal plane wavefront sensors using detectors as close to the science detector as possible. We present seven of them and compare their implementation and efficiency on SCExAO. This work will be critical for wavefront sensing on next generation of extremely large telescopes that might present similar limitations.
We describe the current on-sky performance of the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument on the Subaru telescope on Maunakea, Hawaii. SCExAO is continuing to advance its AO performance, delivering H band Strehl ratios in excess of 0.9 for bright stars. We describe new advances with SCExAO’s wavefront control that lead to a more stable corrected wavefront and diffraction-limited imaging in the optical, modifications to code that better handle read noise suppression within CHARIS, and tests of the spectrophotometric precision and accuracy within CHARIS. We outline steps in the CHARIS Data Processing Pipeline that output publication-grade data products. Finally, we note recent and upcoming science results, including the discovery of new directly-imaged systems and multiwavelength, deeper characterization of planet-forming disks, and upcoming technical advances that will improve SCExAO’s sciencec capabilities.
The Compute and control for adaptive optics (Cacao) is an open source software package providing a flexible framework for deploying real-time adaptive optics control. Cacao leverages CPU and GPU computational resources to meet the demands of modern AO systems with thousands of degrees of freedom running at kHz speed or faster. Cacao adopts a modular approach, where individual processes operate over a standardized data stream stucture. Advanced control loops integrating multiple sensors and DMs are built by assembling multiple such processes. High-level constructs are provided for sensor fusion, where multiple sensors can drive a single physical DM. The common data stream format is at the heart of Cacao, holding data content in shared memory and timing information as semaphores. Cacao is currently in operation on the general-purpose Subaru AO188 system, the SCExAO and MagAOX extreme-AO instruments. Its data stream format has been adopted at Keck, within the COMPASS AO simulation tool, and in the COSMIC modular RTC platform. We describe Cacao’s software architecture and toolset, and provide simple examples for users to build a real-time control loop. Advanced features are discussed, including on-sky results and experience with predictive control and sensor fusion. Future development plans will include leveraging machine learning algorithms for real-time PSF calibration and more optimal AO control, for which early on-sky demonstration will be presented.
The AO188 Single Conjugate facility AO system at Subaru Telescope delivers diffraction-limited images in near-IR in natural and laser guide star modes. We have recently started a major upgrade of AO188 to fulfill the high performance requirements of its downstream instruments, including the Subaru Coronagraphic Extreme-AO. The first phase of this upgrade started in 2017 with the integration of a new real time computer (RTC) and real time system (RTS) CACAO(https://github.com/CACAO-org/CACAO), an open-source real-time software for adaptive optics developed collaboratively and used extensively by the SCExAO instrument. This major upgrade will enable loop optimization, predictive control and include diagnosis tools, therefore improving the performance and stability of AO188 and its downstream instrument module. This paper introduces the architecture of the new RTS describing the different steps we followed to adapt CACAO to our AO interfaces and aging hardware, in preparation of our first engineering tests on-sky achieved successfully on July 23rd 2018.
The compute and control for adaptive optics (cacao) package is an open-source modular software environment for real-time control of modern adaptive optics system. By leveraging many-core CPU and GPU hardware, it can scale up to meet the demanding computing requirements of current and future high frame rate, high actuator count adaptive optics (AO) systems. cacao’s modular design enables both simple/barebone operation, and complex full-featured AO control systems. cacao’s design is centered on data streams that hold real-time data in shared memory along with a synchronization mechanism for computing processes. Users and programmers can add additional features by coding modules that interact with cacao’s data stream format. We describe cacao’s architecture and its design approach. We show that accurate timing knowledge is key to many of cacao’s advanced operation modes. We discuss current and future development priorities, including support for machine learning to provide real-time optimization of complex AO systems.
The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is an extremely modular high- contrast instrument installed on the Subaru telescope in Hawaii. SCExAO has a dual purpose. Its position in the northern hemisphere on a 8-meter telescope makes it a prime instrument for the detection and characterization of exoplanets and stellar environments over a large portion of the sky. In addition, SCExAO’s unique design makes it the ideal instrument to test innovative technologies and algorithms quickly in a laboratory setup and subsequently deploy them on-sky. SCExAO benefits from a first stage of wavefront correction with the facility adaptive optics AO188, and splits the 600-2400 nm spectrum towards a variety of modules, in visible and near infrared, optimized for a large range of science cases. The integral field spectrograph CHARIS, with its J, H or K-band high-resolution mode or its broadband low-resolution mode, makes SCExAO a prime instrument for exoplanet detection and characterization. Here we report on the recent developments and scientific results of the SCExAO instrument. Recent upgrades were performed on a number of modules, like the visible polarimetric module VAMPIRES, the high-performance infrared coronagraphs, various wavefront control algorithms, as well as the real-time controller of AO188. The newest addition is the 20k-pixel Microwave Kinetic Inductance Detector (MKIDS) Exoplanet Camera (MEC) that will allow for previously unexplored science and technology developments. MEC, coupled with novel photon-counting speckle control, brings SCExAO closer to the final design of future high-contrast instruments optimized for Giant Segmented Mirror Telescopes (GSMTs).
Exoplanet imaging requires excellent wavefront correction and calibration. At the Subaru telescope this is achieved us- ing the 188-element facility adaptive optics system(AO188) feeding the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument; a multipurpose instrument built to deliver high contrast images of planets and disks around nearby stars. AO188 offers coarse correction while SCExAO performs fine correction and calibration of 1000 modes. The full system achieves 90%Strehl Ratio in H-band and diffraction limited images. A new Real Time Computer allowing higher performance between SCExAO and AO188 is currently implemented. Future upgrades will include a new Pyramid Wavefront Sensor and (64x64) DM to achieve extreme AO correction inside AO188. We are progressing in the development of predictive control and sensor fusion algorithms across the system to improve performance and calibration. With the new upgrades, SCExAO will be able to image giant planets in reflected light with Subaru and validate technologies necessary to image habitable Earth-like planets with the Thirty Meter Telescope (TMT).
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