This PDF file contains the front matter associated with SPIE Proceedings Volume 12185, including the Title Page, Copyright information, Table of Contents, and Conference Committee Page.

This conference presentation was prepared for the Adaptive Optics Systems VIII conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

The Pathways to Discovery in Astronomy and Astrophysics for the 2020s decadal survey highlighted the ability of the coming generation of 30-meter-class telescopes “to detect, image, and characterize temperate rocky planets around low-mass stars, measure their atmospheric compositions including searches for oxygen.” However, many of the technologies required to reach the challenging contrast ratios associated with this science case are not yet available, and targeted preparatory science must be carried out well in advance of these observations. In this paper, we draw from the example of NASA’s Exoplanet Exploration Program and propose a preliminary version of a “Technology Gap List” and “Science Gap List” for the ground-based imaging of rocky planets around the nearest stars with extremely large ground-based telescopes. These lists can be used to prioritize precursor technical demonstrations and observations with current and near-term high contrast instrumentation, so that the community is ready to exploit the collecting area of extremely large telescopes.

ERIS will extend and enhance the fundamental diffraction limited imaging and spectroscopy capability of the VLT. It combines a 1-5um imaging camera with high contrast capabilities, a 1-2.5um integral field spectrograph, and an adaptive optics system able to work with both LGS and NGS. The instrument has outstanding potential for resolved studies of high redshift galaxies, astrometry in the Galactic Centre, and characterisation of exoplanets. Following an introduction to the instrument, this contribution will present the first results from commissioning - adaptive optics performance, spectral resolution, astrometric precision, and contrast at small angular separations - in terms of the instrument's science drivers and applications.

Today, there exists a wide variety of algorithms dedicated to high-contrast imaging, especially for the detection and characterisation of exoplanet signals. These algorithms are tailored to address the very high contrast between the exoplanet signal(s), which can be more than two orders of magnitude fainter than the bright starlight residuals in coronagraphic images. The starlight residuals are inhomogeneously distributed and follow various timescales that depend on the observing conditions and on the target star brightness. Disentangling the exoplanet signals within the starlight residuals is therefore challenging, and new post-processing algorithms are striving to achieve more accurate astrophysical results. The Exoplanet Imaging Data Challenge is a community-wide effort to develop, compare and evaluate algorithms using a set of benchmark high-contrast imaging datasets. After a first phase ran in 2020 and focused on the detection capabilities of existing algorithms, the focus of this ongoing second phase is to compare the characterisation capabilities of state-of-the-art techniques. The characterisation of planetary companions is two-fold: the astrometry (estimated position with respect to the host star) and spectrophotometry (estimated contrast with respect to the host star, as a function of wavelength). The goal of this second phase is to offer a platform for the community to benchmark techniques in a fair, homogeneous and robust way, and to foster collaborations.

At first light, the NIR instruments of TMT will be assisted by a multi-conjugate adaptive optics instrument, known as the Narrow Field Infrared Adaptive Optics System (NFIRAOS). NFIRAOS will use laser guide stars for distortion correction in a field of view of 2 arcmin diameter, but natural guide stars will be required for tip/tilt correction. A catalogue of guide stars with NIR magnitudes as faint as 22 mags in J band (Vega system), covering the TMT-observable sky will be a critical resource for the efficient operation of NFIRAOS and no catalogue currently exists with objects so faint and cover the entire TMT observable sky. Hence it is essential to develop such a catalogue by computing the expected NIR magnitudes of stellar sources, identified in deep optical sky surveys, by using their optical magnitudes. In this paper, we will discuss a road map created for the generation of the Infrared Guide Star Catalogue (IRGSC) for the TMT using the optical data of stellar sources from the Pan-STARRS observations and computing their NIR magnitudes by using stellar atmospheric models and Spectral Energy Distribution (SED) fits. We have validated the computed NIR magnitudes of the sources in some fields by using the available NIR data for those fields. We find our method to be satisfactory, thereby creating a path for the final production of the IRGSC using the Pan-STARRS and put forward the challenges that need to be overcome in the future development of IRGSC.

We have taken advantage of the implementation of an adaptive optics system on the Themis solar telescope to implement innovative strategies based on an inverse problem formulation for the control loop. Such an approach encompassing the whole system implies the estimation of the pixel variances of the Shack-Hartmann wavefront sensor, a novel real-time method to extract the wavefront slopes as well as their associated noise covariance, and the computation of pseudo-open loop data. The optimal commands are computed by iteratively solving a regularized inverse problem with spatio-temporal constraints including Kolmogorov statistics. The latency of the dedicated real-time control software with conventional CPU is shorter than 300 μs from the acquisition of the raw 400 × 400 pixel wavefront sensor image to the sending of the commands.

ERIS is a new Adaptive Optics (AO) instrument installed at the Cassegrain focus of VLT-UT4 in January 2022 and led by a Consortium of Max-Planck Institut fuer Extraterrestrische Physik, UK-ATC, ETH-Zurich, NOVA-Leiden, ESO and INAF. The ERIS AO system provides NGS mode to deliver high contrast correction and LGS mode to extend high Strehl performance to large sky coverage. The AO module includes one 40x40 LGS wavefront sensor (WFS), one NGS WFS able to switching between 40x40 and 4x4 configuration, the related optics to relay the telescope beam and a dedicated SPARTA real time computer running the AO loop up to 1kHz. The AO module, with the 1170-actuator Deformable Secondary Mirror and the Laser Facility from VLT-AOF, provides AO correction to the high resolution coronagraphic imager NIX (1-5um) and the IFU spectrograph SPIFFIER (1-2.5um). In this paper we briefly review the ERIS AO system design and we present preliminary AO results of the ongoing commissioning, started in February 2022.

We present a status update for MagAO-X, a 2000 actuator, 3.6 kHz adaptive optics and coronagraph system for the Magellan Clay 6.5 m telescope. MagAO-X is optimized for high contrast imaging at visible wavelengths. Our primary science goals are detection and characterization of Solar System-like exoplanets, ranging from very young, still-accreting planets detected at H-alpha, to older temperate planets which will be characterized using reflected starlight. First light was in Dec, 2019, but subsequent commissioning runs were canceled due to COVID19. In the interim, MagAO-X has served as a lab testbed. Highlights include implementation of several focal plane and low-order wavefront sensing algorithms, development of a new predictive control algorithm, and the addition of an IFU module. MagAO-X also serves as the AO system for the Giant Magellan Telescope High Contrast Adaptive Optics Testbed. We will provide an overview of these projects, and report the results of our commissioning and science run in April, 2022. Finally, we will present the status of a comprehensive upgrade to MagAO-X to enable extreme-contrast characterization of exoplanets in reflected light. These upgrades include a new post-AO 1000-actuator deformable mirror inside the coronagraph, latest generation sCMOS detectors for wavefront sensing, optimized PIAACMC coronagraphs, and computing system upgrades. When these Phase II upgrades are complete we plan to conduct a survey of nearby exoplanets in reflected light.

For high contrast imaging, atmospheric turbulence may be sensed and corrected at very high band-width without Wavefront Sensors (WFS) or deformable mirrors using phase correcting integrated photonics devices and advanced signal processing. The overall system employs radio astronomy techniques developed for clock distribution, to sense and correct phase, and radio interferometry procedures to produce high resolution images. One of the tallest poles in high-contrast AO is the frame rate. Our simulation models estimate correction band-width can be 1-2 orders of magnitude faster than current high contrast Adaptive Optics (AO). The method employs a satellite loitering near a science object to send a coded reference laser to the telescope. We have designed and measured a 32 channel astrophotonics phase sensing and correcting device, which is low-cost and compact due to its telecommunications heritage. We are developing a prototype AO system to test the concept, first on a bench and then using a telescope pointed at sources on a tower. This paper also describes how the scheme may be extended to arrays of optical telescopes to give unprecedented micro-arcsecond resolution in the near infrared to obtain image and spectral data cubes of extrasolar planets. The method is also useful for satellite communications, and we have applied for a patent for both astronomy and communications.

Laser Guide Star Adaptive Optics (LGSAO) systems require an optical relay to produce images of both the telescope focal surface, and of laser guide stars. Laser guide stars imaged by the telescope lie at a range of axial distances from the telescope focal surface. Further, such relays are required to produce sharp metapupils and exit pupil. “Absolute Instruments” are optical systems which provide an image of the entire 3-dimensional object-space of the system that is free of distortion, curvature and point-blurring aberrations. Such systems are well-matched to the requirements of LGSAO systems. In this paper it will be shown that such systems can provide excellent image quality for the science field as well as for any practical range of LGS objects. Further, by splitting the correcting plate that transforms an ordinary relay into an absolute instrument, simultaneous near-perfect correction of metapupils and exit pupil can be achieved with no compromise to the relays’ imaging properties.

Current state-of-the-art adaptive optics (AO) provides ground-based, diffraction-limited observations with high Strehl ratios (SR). However, a detailed knowledge of the point spread function (PSF) is required to fully exploit the scientific potential of these data. This is even more crucial for the next generation AO instruments that will equip 30-meter class telescopes, as the characterization of the PSF will be mandatory to fulfill the planned scientific requirements. For this reason, there is a growing interest in developing tools that accurately reconstruct the observed PSF of AO systems, the so-called PSF reconstruction. In this context, a PSF-R service is a planned deliverable for the MICADO@ELT instrument and our group is in charge of its development. In the case of MICADO, a blind PSF-R approach is being pursued to have the widest applicability to science cases. This means that the PSF is reconstructed without extracting information from the science data, relying only on telemetry and calibrations. While our PSF-R algorithm is currently being developed, its implementation is mature enough to test performances with actual observations. In this presentation we will discuss the reliability of our reconstructed PSFs and the uncertainties introduced in the measurements of scientific quantities for bright, on-axis observations taken with the SOUL+LUCI instrument of the LBT. This is the first application of our algorithm to real data. It demonstrates its readiness level and paves the way to further testing. Our PSF-R algorithm is able to reconstruct the SR and full-width at half maximum of the observed PSFs with errors smaller than 2% and 4.5%, respectively. We carried out the scientific evaluation of the obtained reconstructed PSFs thanks to a dedicated set of simulated observations of an ideal science case.

Speckle Noise is the dominant source of error in high contrast imaging with adaptive optics system. We discuss the potential for wavefront sensing telemetry to calibrate speckle noise with sufficient precision and accuracy so that it can be removed in post-processing of science images acquired by high contrast imaging instruments. In such a self-calibrating system, exoplanet detection would be limited by photon noise and be significantly more robust and efficient than in current systems. We show initial laboratory and on-sky tests, demonstrating over short timescale that residual speckle noise is indeed calibrated to an accuracy exceeding readout and photon noise in the high contrast region. We discuss immplications for the design of space and ground high-contrast imaging systems.

We develop a covariance-based analytical algorithm to efficiently predict the performance of complex tomographic AO systems based Shack-Hartmann WFSs (SH-WFS). The algorithm produces a predicted point spread function (PSF) and a decomposed wavefront error for each error term and is implemented using GPU and CUDA libraries for efficient computation. In this paper, we introduce the basis of our algorithm and show the prediction results, computational speed, and comparison with end-to-end simulations for the ULTIMATE-SUBARU GLAO and LTAO systems as test cases.

Large amounts of Adaptive-Optics (AO) control loop data and telemetry are currently inaccessible to end-users. Broadening access to those data has the potential to change the AO landscape on many fronts, addressing several use-cases such as derivation of the system’s PSF, turbulence characterization and optimization of system control. We address one of the biggest obstacles to sharing these data: the lack of standardization, which hinders access. We propose an object-oriented Python package for AO telemetry, whose data model abstracts the user from an underlining archive-ready data exchange standard based on the Flexible Image Transport System (FITS). Its design supports data from a wide range of existing and future AO systems, either in raw format or abstracted from actual instrument details. We exemplify its usage with data from active AO systems on 10m-class observatories, of which two are currently supported (AOF and Keck), with plans for more.

Photonic technologies offer more and more possibilities for instrumentation requiring guided waves and original mixing of electric fields, all in one robust and compact component. At the Subaru telescope, there are several photonic-based instruments installed on the SCExAO platform, namely the FIRST spectro-interferometer in the visible and the GLINT nuller in the IR. Thanks to the interferometric recombination of different parts of the pupil, this kind of instrument gives access to spatial scales below the diffraction limit of the telescope, thus providing super-resolution capability. On top of that, the idea of exploiting the interferometric observables to feed the AO correction loop, including especially exotic modes such as the low wind effect, is under study and practical experimentation within the FIRST instrument. This approach, directly based on the science data, offers promising and exciting prospects for both wavefront sensing techniques and exoplanet science.

“Super-resolution” (SR) refers to a combination of optical design and signal processing techniques jointly employed to obtain reconstructed wave-fronts at a higher-resolution from multiple low-resolution samples, overcoming the inherent limitations of the latter. After compelling performance gain obtained both in simulations and on-sky [presented at this conference] using Shack-Hartmann wave-front sensors (WFS) with laser guide-stars, we broaden its application domain to pyramid (P-)WFS. We revisit the analytic P-WFS diffraction model to show the “what, how, when and why” SR can be employed, evaluating its gains under turbulent and non-turbulent (e.g. pupil fragmentation) conditions. Results: We show that a super-resolved P-WFS is more resilient to mis-registration, lifts alignment requirements and improves performance (against alialiasing and other spurious modes AOsystems are poorly sensitive to) with only a factor up to 2 increased computational burden.

We present the results obtained with an end-to-end simulator of an Extreme Adaptive Optics (XAO) system control loop. It is used to predict its on-sky performances and to optimise the AO loop algorithms. It was first used to validate a novel analytical model of the fitting error, a limit due to the Deformable Mirror (DM) shape. Standard analytical models assume a sharp correction under the DM cutoff frequency, disregarding the transition between the AO corrected and turbulence dominated domains. Our model account for the influence function shape in this smooth transition. Then, it is well-known that Shack-Hartmann wavefront sensors (SH-WFS) have a limited spatial bandwidth, the high frequencies of the wavefront being seen as low frequencies. We show that this aliasing error can be partially compensated (both in terms of Strehl ratio and contrast) by adding priors on the turbulence statistics in the framework of an inverse problem approach. This represents an alternative to the standard additional optical filter used in XAO systems. In parallel to this numerical work, a bench was aligned to experimentally test the AO system and these new algorithms comprising a DM192 ALPAO deformable mirror and a 15x15 SH-WFS. We present the predicted performances of the AO loop based on end-to-end simulations.

This conference presentation was prepared for the Adaptive Optics Systems VIII conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

Most simulation packages for adaptive optics require some sort of deformable mirror (DM) model. A static model based on influence functions or spatial frequencies is usually enough for frame-by-frame simulations. But advanced AO systems are pushing the technology limits, and temporal effects in each component must be taken into account and simulated. This paper presents how FEM simulations and state-space differential equations can be combined to build a fully dynamic DM model which is at the same time very accurate and computationally light. This opens the path to end-to-end dynamic AO models that can be used for example to develop or pre-train advanced controllers based on neural networks.

It is common practice in adaptive optics to use CCD detectors with global shutter readout for wavefront sensing. sCMOS detectors with rolling shutter readout are often not considered due to image distortion when the object is moving at high speed. However, sCMOS detectors have the potential to achieve lower readout noise, larger format, and lower cost. Therefore, we investigate the effect of rolling shutter readout in the context of the laser guide star wavefront sensors of ULTIMATE-Subaru, a Ground Layer Adaptive Optics project at the Subaru telescope. In the case of a laser guide star wavefront sensor, the wavefront tip-tilt component is filtered out in the measurement due to the tip-tilt indetermination effect. With the rolling shutter readout, the tip-tilt component can alias onto the higher-order wavefront components, it becomes a problem for the wavefront measurement. Firstly, we identify the particular modes that are aliased onto, as well as the frequency response of this aliasing. As a result, it is confirmed that when the oscillation frequency of tip-tilt is faster than about 10% of the sampling frequency of the detector, it is partially measured as higher-order components such as coma and trefoil. We also conduct a wavefront measurement experiment using the ORCA-Flash4.0 v2 sCMOS detector manufactured by Hamamatsu Photonics. The experiment with the optical system shows consistent results as the simulation. Finally, we estimate the effect of aliasing from the tip-tilt components of the atmospheric turbulence, telescope vibration, and laser guide star jitter using a end-to-end adaptive optics simulation.

A new era of ground-based observations, either in the infrared with the next-generation of 25-40m extremely large telescopes or in the visible with the 8m Very Large Telescope, is going to be assisted by multi-conjugate adaptive optics (MCAO) to restore the unprecedented resolutions potentially available for these systems in absence of atmospheric turbulence. Astrometry is one of the main science drivers, as MCAO can provide good quality and uniform correction over wide field of views (∼ 1 arcmin) and offer a large number of reference sources with high image quality. The requirements have been set to very high precisions on the differential astrometry (e.g. 50μas for MICADO/MORFEO - formerly known as MAORY - at the Extremely Large Telescope) and an accurate analysis of the astrometric error budget is needed. In this context, we present an analysis of the impact of MCAO atmospheric tip-tilt residuals on relative astrometry. We focus on the effects of the scientific integration time on tip-tilt residuals, that we model through the temporal transfer function of the exposure. We define intraand inter-exposure tip-tilt residuals that we use in the estimation of the centroiding error and the differential tilt jitter error within the astrometric error budget. As a case study, we apply our results in the context of the MORFEO astrometric error budget.

SIGHT is a new approach to adaptive optics emphasizing panchromatic image sharpening from 360 nm – 2500 nm with specific intent to increase spectrograph observing sensitivity and operational efficiency. Utilizing a single, pilot-safe ultraviolet (invisible) Rayleigh laser guide star (LGS), we prioritize all-sky seeing enhancement and energy concentration, with minimal observing overheads, over absolute spatial resolution. We accomplish this by releasing the system requirement for natural guide star (NGS) tip-tilt wavefront sensing, seeking instead partial tip-tilt information obtainable with LGS telemetry alone. By implementing an ultra-compact (17 cm x 20 cm x 56 cm) parfocal AO relay installed permanently ahead of the Cassegrain focus, we enable high-spatial-frequency AO correction over a field of view of up to 30 arcseconds in diameter. The development of AO differentiated for specific scientific goals represents a further maturation of AO technology beyond the gilded cage of Strehl ratio

We present the status and plans for the Keck All sky Precision Adaptive optics (KAPA) program. KAPA includes (1) an upgrade to the Keck I laser guide star adaptive optics (AO) facility to improve image quality and sky coverage, (2) the inclusion of AO telemetry-based point spread function estimates with all science exposures, (3) four key science programs, and (4) an educational component focused on broadening the participation of women and underrepresented groups in instrumentation. For this conference we focus on the KAPA upgrades since the 2020 SPIE proceedings1 including implementation of a laser asterism generator, wavefront sensor, real-time controller, asterism and turbulence simulators, the laser tomography system itself along with new operations software and science tools, and modifications to an existing near-infrared tip-tilt sensor to support multiple natural guide star and focus measurements. We will also report on the results of daytime and on-sky calibrations and testing.

The classical single conjugate adaptive optics system of the new 4-meter Daniel K. Inouye Solar Telescope is going to be replaced by a multi-conjugate system for adaptive optics supported observations of the Sun in an enlarged field of view. The multi-conjugate correction will expand the high-order adaptive optics wavefront correction over a wider field of view up to 1 arcminute. The ground-layer-only correction will uniformly improve the seeing across a field of view larger than 2 arcminutes for observations that require lower resolution but very large fields. Thus, the ground-layer & multi-conjugate adaptive optics upgrade will add new potential to the wavefront correction system and thereby boost the scientific output of the telescope. In this conference, we layout the overall project, its subsystems and the current status.

New generation exoplanet imagers on large ground-based telescopes are highly optimised for the detection of young giant exoplanets in the near-infrared, but they are intrinsically limited for their characterisation by the low spectral resolution of their integral field spectrographs (R < 100). High-dispersion spectroscopy at R ≫ 10⁴ would be a powerful tool for the characterisation of these planets, but there is currently no high-resolution spectrograph with extreme adaptive optics and coronagraphy that would enable such characterisation. With project HiRISE we propose to use fiber coupling to combine the capabilities of two flagship instruments at the Very Large Telescope in Chile: the exoplanet imager SPHERE and the high-resolution spectrograph CRIRES+. The coupling will be implemented at the telescope in early 2023. We provide a general overview of the implementation of HiRISE, of its assembly, integration and testing (AIT) phase in Europe, and a brief assessment of its expected performance based on the final hardware.

MAVIS (the MCAO Assisted Visible Imager & Spectrograph) will be driven by a high performance real-time control (RTC) system relying on cutting edge hardware and software technologies, including the hard real-time pipeline as well as the supervisory and tightly coupled telemetry sub-systems. To meet the extremely challenging requirements of a complex instrument like MAVIS, this forward looking implementation of the COSMIC platform is designed to support, end-to-end, a wide range of control schemes, from classical model-based approaches up to modern data-driven methodologies. In this paper, we will review the design and prototyping activities being led during phase B of the project.

In July of 2020 the Herzberg Astronomy and Astrophysics Research Centre was contracted to provide the Gemini Telescopes Observatory with a facility class Adaptive Optics (AO) Real Time Controller (RTC) suitable to run existing and future Adaptive Optics Systems. This Gemini Adaptive Optics Real-Time Controller (GAO RTC) is using the Herzberg Extensible Adaptive Real-time Toolkit (HEART), a C/Python software framework for constructing RTCs that targets general-purpose CPUs and standard networking hardware. Initially a fully simulated stand-alone RTC will be completed which will be suitable for experimentation in association with end-to-end AO simulation software. Subsequently, it will be reconfigured and extended to support hardware interfaces to the future Gemini North Adaptive Optics (GNAO) facility. This paper will provide an overview of the customization of the HEART design for GNAO, current state of the development, how this system state changes during operation, and how HEART was de-risked.

The W. M. Keck Observatory Adaptive Optics (AO) facilities have been operating with a Field Programmable Gate Array (FPGA) based real time controller (RTC) since 2007. The RTC inputs data from various AO wavefront and tip/tilt sensors; and corrects image blurring from atmospheric turbulence via deformable and tip/tilt mirrors. Since its commissioning, the Keck I and Keck II RTCs have been upgraded to support new hardware such as pyramid wavefront and infrared tip-tilt sensors. However, they are reaching the limits of their capabilities in terms of processing bandwidth and the ability to interface with new hardware. Together with the Keck All-sky Precision Adaptive optics (KAPA) project, a higher performance and a more reliable RTC is needed to support next generation capabilities such as laser tomography and sensor fusion. This paper provides an overview of the new RTC system, developed with our contractor/collaborators (Microgate, Swinburne University of Technology and Australian National University), and the initial on-sky performance. The upgrade includes an Interface Module to interface with the wavefront sensors and controlled hardware, and a Graphical Processing Unit (GPU) based computational engine to meet the system’s control requirements and to provide a flexible software architecture to allow future algorithms development and capabilities. The system saw first light in 2021 and is being commissioned in 2022 to support single conjugate laser guide star (LGS) AO, along with a more sensitive EMCCD camera. Initial results are provided to demonstrate single NGS & LGS performance, system reliability, and the planned upgrade for four LGS to support laser tomography.

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.

The next generation of Giant Fragmented Telescopes will allow the study of faint and distant objects such as exoplanets. But the structure of the telescope also brings new challenges such as pupil fragmentation or Low- Wind Effect (LWE) that needs to be corrected by the Adaptive Optics (AO) system. The Wave-Front Sensor (WFS) which is the heart of the AO system needs to be able to measure these aberrations. Because of its high sensitivity, the Zernike Wave-Front Sensor (ZWFS) appears to be a viable candidate as a 2^nd stage instrument to measure telescope seeing or differential piston. However, its use is limited by its small dynamic range. We propose here a new concept of WFS based on the ZWFS with a better dynamic range : the Phase Shifted ZWFS (Phase-Shifted ZWFS).

Uncorrected residual wavefront errors limit the ultimate performance of adaptive optics (AO) systems. We present different contributing factors and techniques to estimate and compensate these wavefront errors in the Keck natural guide star (NGS) AO systems. The error terms include low order static and semi-static aberrations from multiple sources, periodic and random segment piston errors, single-segment low order aberrations, wavefront sensor aliasing, vibrations, calibration drifts, and AO-to-telescope offload related errors. We present the design of a new AO subsystem, a residual wavefront controller (rWFC) to monitor the performance of the AO control loops and the image quality of the AO science instruments and apply the necessary changes to the telescope and AO parameters to minimize the residual wavefront errors. The distributed system consists of components at the telescope, AO bench and the science instruments. A few components of this system are already tested as on-demand standalone tools and will be integrated into a high-level graphical user interface (GUI) to operate the system. The software tool will periodically collect AO telemetry data, perform control loop parameter optimization and update AO parameters such as loop gains, centroid gain, etc. In addition, the system will analyze the science data at the end of each exposure and estimate telescope/AO performance when a bright point source is available in the science field. The benefits of reducing or eliminating the residual wavefront errors have broad implications for optical astronomy. Testing these techniques on a segmented telescope will be extremely useful to the teams developing high contrast AO systems for all extremely large telescopes and future segmented space telescopes.

Low wind and petaling effects, caused by the discontinuous apertures of telescopes, are poorly corrected - if at all - by commonly used workhorse wavefront sensors (WFSs). Wavefront petaling breaks the coherence of the point spread function core, splitting it into several side lobes, dramatically shutting off scientific throughput. 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 formed from a 7-hole mask are used for direct retrieval of petaling aberrations, which are almost invisible to the main AO loop. We implement a visible light dual-band SAM mode, using two disjoint 25 nm wide channels, that we recombine to overcome the one-lambda ambiguity of fringe-tracking techniques. This enables a control over petaling with sufficient capture range yet without con icting with coronagraphic modes in the near-infrared. We present on-sky engineering results demonstrating that the design is able to measure petaling well beyond the range of a single-wavelength equivalent design.

On-sky testing is a key step in taking an instrumentation concept from the laboratory to deployment within a facility-class instrument. Access to dedicated test facilities can help reduce the cost and time associated with this process, particularly concepts that rely on the use of Adaptive Optics. The H2020 OPTICON-RadioNet Pilot (ORP) program is funding access time specifically for testing new visitor instrument concepts using the facilities developed for CANARY and LGS AO experiments. Here we provide further details of the facilities and support that is being offered and give details of the call for proposals for visiting experiments for 2023.

The high-speed variability of the local water vapor content in the Earth atmosphere is a significant contributor to ground-based wavefront quality throughout the infrared domain. Unlike dry air, water vapor is highly chromatic, especially in the mid-infrared. This means that adaptive optics correction in the visible or near-infrared domain does not necessarily ensure a high wavefront quality at longer wavelengths. Here, we use literature measurements of water vapor seeing, and more recent infrared interferometric data from the Very Large Telescope Interferometer (VLTI), to evaluate the wavefront quality that will be delivered to the METIS mid-infrared camera and spectrograph for the Extremely Large Telescope (ELT), operating from 3 to 13 μm, after single-conjugate adaptive optics correction in the near-infrared. We discuss how the additional wavefront error due to water vapor seeing is expected to dominate the wavefront quality budget at N band (8–13 μm), and therefore to drive the performance of mid-infrared high-contrast imaging modes at ELT scale. Then we present how the METIS team is planning to mitigate the effect of water vapor seeing using focal-plane wavefront sensing techniques, and show with end-to-end simulations by how much the high-contrast imaging performance can be improved.

METIS is the European Extremely Large Telescope (ELT) 1st-generation Mid-Infrared ELT Imager and Spectrograph. It will offer spectroscopic, imaging and coronagraphic capabilities from 3 up to 13 microns with Adaptive-Optics correction.

With its Final Design Review due late 2022 we report on the wavefront control strategy devised to meet the METIS science and technological requirements. Such strategy addresses challenging aspects as i) the appearance of differential petal piston modes in the presence of secondary mirror support struts caused either by numerical processing or the actual, physical low-wind effect, ii) the numerical pupil derotation and mis-reg compensation, iii) the adaptation to transient disturbance signals such as telescope-to-instrument handover control and iv) the compliance with constrained modal control of the pre-focal beam corrector mirrors (M4/M5).

The overall METIS wavefront control strategy consists in a split approach cemented in a sequence of steps: 1) Tikhonov-regularised spatial wavefront estimation/reconstruction on a zonal Cartesian coordinate system tied to the pyramid (P-WFS) sampling pixel grid, 2) the regularised projection onto a global modal control space including correction of mis-registrations and rotation between the P-WFS coordinate grid and the ELTs M4/M5, and 3) the time-filtering through the application of proportional-integral control before converting to actuator commands readied for the ELTs collaborative TT off-loading scheme whilst avoiding hitting the mirrors constraints in amplitude, speed and force.

We present physical-optics simulation results of the whole AO system obtained with prototyped instances of the real-time and soft-real-time computers including sensitivity analysis with respect to observational, atmospheric, non-atmospheric (telescope-intrinsic such as wind-induced low-order modes comprising tip-tilt) and instrument-specific conditions and disturbances.

An error budget is put together that meets the METIS science requirements in terms of wavefront error with reassuring margins thus endorsing the strategy devised.

We present a novel type of nonlinear reconstructor for all Fourier-type wavefront sensors like the Pyramid Wavefront Sensor. Different to interaction matrix approaches which critically degrade image quality due to approximation errors in nonlinear regimes, the new wavefront estimation algorithm has been designed to be robust in such frameworks. It works by employing an iterative technique to circumvent the major drawbacks associated with linear methods. A significant advantage to this approach is that the developed nonlinear algorithm is a generalised wavefront reconstruction method meaning that the reconstructor is directly applicable to any Fourier-type WFS.

MORFEO (formerly known as MAORY) is a post-focal adaptive optics module that forms part of the first light instrument suite for the Extreme Large Telescope (ELT). The project passed the Preliminary Design Review in two stages in April and July 2021 and is now entering the Final Design Phase. In this paper we report the status of the project.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. In this paper, we present the system choices that have been made for the SCAO and LTAO modules. We describe the strategy developed for the different Wave-Front Sensors: pyramid for SCAO, the LGSWFS concept, the NGSWFS path, and the truth sensor capabilities. With this talk we intend to provide a general overview of the performance and operations for the AO modes of HARMONI. As such, we will also present the overall integration of the AO modules within the HARMONI instrument, and a full end-to-end simulation of the expected performance once at the telescope

The Giant Magellan Telescope (GMT) design consists of seven circular 8.4-m diameter mirror segments that are separated by large > 30 cm gaps, making them susceptible to fluctuations in optical path differences (piston) due to flexure, segment vibrations, wind buffeting, temperature effects, and atmospheric seeing. If we wish to utilize the full 25.4-m diffractionlimited aperture of the GMT for high-contrast natural guide star adaptive optics (NGSAO) science (e.g., direct imaging of habitable zone earth-like planets around late type stars), the seven mirror segments must be co-phased to well within a fraction of a wavelength. The current design of the GMT involves seven adaptive secondary mirrors, a dispersed fringe sensor, and a pyramid wavefront sensor (PyWFS) to measure and correct the total path length between segment pairs, but these methods need to be tested “end-to-end” in a lab environment if we hope to officially retire the GMT high risk item of phasing performance. We present the design and working prototype of a “GMT High-Contrast Adaptive Optics phasing Testbed” (p-HCAT) which leverages the existing MagAO-X ExAO instrument to demonstrate segment phase sensing and simultaneous AO-control for high-contrast GMT NGSAO science. We present the first test results of closed-loop piston control with one GMT segment using MagAO-X’s PyWFS and a novel Holographic Dispersed Fringe Sensor (HDFS) with and without simulated atmospheric turbulence. We show that the PyWFS alone was able to successfully control piston without turbulence within 12-33 nm RMS for 0 λ/D – 5 λ/D modulation, but was unsuccessful at controlling segmented piston with generated ∼ 0.6 arcsec and ∼ 1.2 arcsec seeing turbulence due to non-linear modal cross-talk and poor pixel sampling of the segment gaps on the PyWFS detector. We report the success of an alternate solution to control segmented piston using the novel HDFS while controlling all other modes with the PyWFS purely as a slope sensor (piston mode removed). This “second channel” WFS method worked well to control piston to within 50 nm RMS and ± 10 μm dynamic range under simulated 0.6 arcsec and 1.2 arcsec atmospheric seeing conditions. These results suggest that a PyWFS alone is not an ideal piston sensor for the GMT and likely other Giant Segmented Mirror Telescopes (GSMTs) as well. Therefore, an additional “second channel” piston sensor, such as the novel HDFS, is strongly suggested.

The Natural Guidestar Adaptive Optics (NGAO) system of the Giant Magellan Telescope (GMT) uses a visible-light modulated pyramid wavefront sensor (PWFS) to measure the wavefront aberrations, including residual segment piston errors. This paper presents an updated wavefront sensing and control architecture that increases the robustness of segment piston control. In the first place, the Natural Guide star Wavefront Sensor (NGWS) design has been updated to incorporate the recently proposed Holographic Dispersed Fringe Sensor (HDFS) as a second wavefront sensing channel measuring unambiguously differential segment piston errors as large as ~14 microns. In the second place, an optimized modal control strategy has been developed to compensate mode-by-mode for the optical gain of the PWFS. We report on the simulated NGAO performance results obtained when using a R=12 guide star, and with a turbulence strength of 𝑟₀ =12.8 cm.

One of the greatest technical challenges of the doubly-segmented Giant Magellan Telescope is the accurate and stable control of segment piston in the diffraction limited observation mode. To address this challenge, in collaboration with the University of Arizona, Smithsonian Astrophysical Observatory and the Istituto Nazionale di Astrofisica, GMTO is executing a project to optimize and validate segment piston control strategies and algorithms using a pair of testbeds. The testbeds provide disturbances to simulate atmospheric turbulence and differential atmospheric dispersion. In addition to the phasing demonstration, the testbeds offer the opportunity to validate hardware designs for the Acquisition & Guiding Wavefront Sensor (AGWS) and the Natural Guide Star Wavefront Sensor (NGWS) and to mitigate their fabrication and assembly risks. Significant progress is reported in the design of the AGWS and NGWS prototypes as well as preliminary test results from the testbeds.

The Extremely Large Telescope [ELT] is the future large European optical observatory. It will offer to astronomical community a unique high angular resolution of 12 mas in K band. The diffraction limit on such a telescope can only be met by using adaptive optics systems in order to compensate for the atmospheric perturbations as well as the telescope and instrument aberrations. The large spiders (50cm width) of the telescope are the source of strong wave-front fragmentation that prevent from reaching the diffraction limit. Among them, the low wind effect is a large expected wave-front discontinuity brought by the temperature gradient around the spiders. In this paper, we analyse the expected impact of such an aberration on the performance of the AO system, in the case of a first generation SCAO system on ELT. We also analyse its impact on the AO WFS. Lastly, we explore possible solution for HARMONI-SCAO and analyse their potential performance.

General purpose adaptive optics are poorly suited to handling wavefront modes that naturally occur or are amplified by discontinuities introduced by the telescope and its surrounding structure. This limitation, whose devastating effects were revealed by extreme adaptive optics fed high-contrast imaging instruments experiencing low wind effect conditions, is expected to be even more severe for the next generation of giant segmented telescopes (GST) that generally feature numerous stronger discontinuities. Another astrophysical high-angular resolution tool, long baseline optical interferometry, is regularly tackling this problem and is perfectly able to co-phase an array, with sub-precision, even in the presence of large initial piston excursions. One way to solve for the so-called petal-mode problem is to interferometric solutions to the GST scenario. One approach is to use a sparse aperture mask (SAM) in a plane conjugated with the pupil of the telescope and exploit the information present in the resulting Fizeau interferograms. Traditionally, SAM are used for astrophysical purposes, and are therefore part of instruments: the masks are non-redundant (see Deo et al, this conference), which optimizes the Fourier sampling but is not optimized for metrology. This paper introduces a partially redundant mask design that provides better sensitivity to the petal modes, shows how to go from interferograms to a full description of the petal modes using simulations, and looks at how to implement this solution as part of the telescope, possibly even ahead of the adaptive optics, using the European ELT as a study case.

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics (AO) modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews.

The SCAO system for HARMONI is based on a pyramid wavefront sensor (PWFS) operating in the visible (700 – 1000 nm). Previous implementations on very large telescopes have demonstrated the challenges associated with optimising PWFS performance on-sky, particularly when operated at visible wavelengths. ELT operation will pose further challenges for AO systems, particularly related to the segmentation of the telescope and the control of badly seen ‘petal modes’. In this paper we investigate these challenges in the context of the HARMONI SCAO system. We present the results of end-to-end simulations of our baseline approach, using a coupled control basis to avoid the runaway development of petal modes in the control loop. The impact of key parameters are investigated and methods for optical gain compensation and optimisation of the control basis are presented. We discuss recent updates to the control algorithms and demonstrate the possibility of improving performance using a form of super resolution. Finally, we report on the expected performance across a range of conditions.

The Giant Magellan Telescope (GMT) wavefront control system provides active optics control and optical turbulence correction for every instrument on the 25.4 m diameter GMT. The GMT has four first-generation wavefront control modes that balance image quality, field of view, sky coverage, and development risk: Natural Seeing, Ground-Layer AO, Natural Guide Star AO, and Laser Tomography AO. Several aspects of the GMT wavefront control design have been recently updated. The Acquisition, Guiding, and Wavefront Sensing Subsystem, used in all control modes, has completed final design and a full-scale prototype sensor is being assembled. A Holographic Dispersed Fringe Sensor has been developed to improve the segment phasing capture range and stability of the Natural Guide Star AO mode. In the Laser Tomography AO mode, a high-speed infrared imager in each instrument will measure segment phasing disturbances using phase retrieval on a faint natural guide star, replacing an inter-segment differential laser metrology truss as the primary phasing sensor. High-fidelity simulations of all wavefront control modes have been developed, and we are developing wavefront sensor prototypes on laboratory testbeds that replicate the GMT optical design. We review the performance expectations in each control mode, and describe our plan to complete the wavefront control system development.

In the context of the European Southern Observatory (ESO) Extremely Large Telescope (ELT), MICADO will be the first light near infrared imager planned to be on sky in 2027. The AO system for MICADO includes a Single Conjugate AO (SCAO) mode, developed by CNRS in France, to control ELT M4 and M5 mirrors from a pyramid wavefront sensor (PWFS).

The final design of the SCAO real-time computer (RTC) leverages the COSMIC platform for the hard-RTC (H-RTC) which implements the AO real-time operations, and the ESO RTC toolkit for the soft-RTC (S-RTC) which implements optimization operations, monitoring and command interfaces with the instrument. In this paper, we present the final design of the MICADO SCAO RTC which fully comply with ESO requirements and standards. We will show how both the COSMIC platform and the ESO RTC Toolkit are integrated together and we will provide the first performance results obtained in the prototyping activities.

The adaptive optics systems for the next generation of extremely large telescopes have in some cases exceeded the capabilities of single computers and servers. The next generation of real-time control systems for these adaptive optics systems often consist of multiple “nodes” connecting into a real-time system, with supplementary computers which optimise and supervise the real-time loop. In this presentation we will give an overview of the approach we are taking to the HARMONI Adaptive Optics control system. We will describe the approach we have taken in designing, modelling, and building a real time control system for this scale of instrument.

Laser Guide Star wave-front sensing [LGSWFS] is a key element of tomographic Adaptive Optics system. For classical Shack-Hartmann Wave-Front Sensor, necessary trade-offs have to be made between the pupil spatial sampling, the sub-aperture field-of-view and the pixel sampling. For Extremely Large Telescope [ELT] scales, these trade-off are also driven by strong technical constraints, especially concerning the available detectors. We propose a sensitivity analysis, and we explore how these parameters impacts the final performance. We introduce the concept of super resolution, which allows to reduce the pupil sampling and allows proposing potential LGSWFS designs providing the best performance for ELT scales.

The adaptive optics (AO) system requires natural guide stars (NGS) to differentiate the focus error generated due to vertical shift in the sodium centroid altitude together with atmospheric turbulence. This dependency on NGS restricts achieving useable sky coverage and AO operation during dawn. One of the proposed approaches to distinguish these two focus errors is to monitor continuously the region of the sodium layer where the LGS is generated. The classical approaches used for this task, direct imaging, and LIDAR technology, have limitations. The technique of continuously amplitude modulating the guidestar laser (GSL) according to the pseudo-random binary sequence (PRBS) has the potential to overcome the limitations of classical approaches and reduce the dependency of the AO system on the NGS. The focus error is the major issue in large telescopes; therefore, we extended the PRBS technique to one of the large telescopes, the Gaint Magellan Telescope through numerical simulations. The study shows that modulation strength of 0.47 is required to fulfil the requirements during high sodium column density. Previously, it was intended to experimentally verify the technique with an LGS facility installed at the 1.8 m EOS telescope, Mount Stromlo, Canberra, Australia. Due to unavoidable circumstances, we now intend to perform the experiment with the LGS facility at the 2.3 m ANU telescope, Siding Spring Observatory (SSO), Coonabarabran, Australia. The paper presents the numerical simulations conducted with parameters of SSO, hardware selection for the experiment based on the system requirements, and preliminary test results from the laboratory.

Pixel processing for laser guide star (LGS) Shack-Hartman wavefront sensor (WFS) is often based on center of gravity with thresholding (tCoG) algorithm, which yields close to linear response but with zero point corrupted by the shape of the source (sodium profile). The spot truncation due to the limited field of view of the WFS sub-apertures, as well as non-common path aberration (NCPA) further complicate the problem. Natural guide star (NGS) based truth wavefront sensors (TWFS) are therefore often used to correct the resulting aberrations, and multiple such TWFS are required to control anisoplanatism effects when there are multiple LGS. In this paper, we demonstrate a novel algorithm that reconstructs the sodium profile from time averaged subaperture images of one or multiple LGS WFS using a system imaging model which can then be used to improve the pixel processing by correcting the tCoG reference vector. It forgoes the need for using any NGS based TWFS for sodium profile induced aberrations and a single TWFS would then be sufficient to monitor optics effects. The reconstructed sodium profile can also be used to build constrained matched filters, a novel pixel processing algorithm alternative to tCoG that requires accurate knowledge of the subaperture reference images and their derivatives and has yet to be demonstrated on sky. Consequently, this new sodium profile reconstruction algorithm eliminates the need for dithering LGS spots on sky, which greatly simplifies the implementation of matched filtering, and also provides better performance. All the pixel processing optimizations can be done with a modern CPU at around 0.1 Hz update rate as a background process for the real time controller. The simulations we have done are for center launch LGS, but we are confident the profile estimation algorithm should work equally well if not better for side launch LGS even when there is truncation.

Commonly used wavefront sensors - the Shack Hartmann wavefront sensor and the pyramid wavefront sensor, for example - have large dynamic range or high sensitivity, trading one regime for the other. A new type of wavefront sensor is being developed and is currently undergoing testing at the University of Arizona’s Center for Astronomical Adaptive Optics. This sensor builds on linear optical differentiation theory by using linear, spatially varying half-wave plates in an intermediate focal plane. These filters, along with polarizing beam splitters, divide the beam into four pupil images, similar to those produced by the pyramid wavefront sensor. The wavefront is then reconstructed from the local wavefront slope information contained in these images. The ODWFS is ideally suited for wavefront sensing on extended objects because of its large dynamic range and because it operates in a pupil plane which allows for on chip resampling even for arbitrarily shaped sources. We have assembled the ODWFS on a testbed using a 32 x 32 square 1000 actuator deformable mirror to introduce aberration into a simulated telescope beam. We are currently testing the system’s spatial frequency response and are comparing the resulting data to numerical simulations. This paper presents the results of these initial experiments.

The Ingot WFS represents an innovative and indispensable class of sensors conceived to overcome some limitations due to the LGSs geometry, which is significantly different from the point-object originated by a NGS. Here we overview the project, aiming at investigating the performance of an ELT-like telescope equipped with the Ingot WFS, facing different aspects of the program: the needs for numerical simulations and laboratory experiments, the prototype and, finally the future plan for the verification on sky.

This conference presentation was prepared for the Adaptive Optics Systems VIII conference at SPIE Astronomical Telescopes + Instrumentation, 2022.

We describe the new atmospheric optical turbulence profiler FASS (Full Aperture Scintillation Sensor). Based on scintillation, the instrument uses a fast and low-noise detector to record and process sequences of scintillation images. Statistical processing of these data is based on the calculation of power spectra of intensity in annular pupil zones over the angular coordinate. The angular power spectra are used to measure the optical turbulence intensity of 14 layers located at logarithmically spaced distances from 0 to 25 km. The reference functions relating turbulence strength to the angular power spectra are computed by numerical simulation. Measurement of the ground-layer turbulence and total seeing with FASS is possible as the detector is optically conjugated below ground (negative distance). Results of measurement campaigns at different observatories are reported, showing a good agreement of turbulence profiles measured by FASS with two other instruments, SCIDAR and MASS.

Remote measurements of optical turbulence profiles are nowadays performed by statistical analysis of either scintillation or the wavefront slope. Here I propose to detect the wavefront curvature and compute its spatio-angular covariance by a triangulation technique to determine optical turbulence profiles. This potential new method called Curvature Detection and Ranging (CURDAR) is theoretically studied in this letter. The width of the curvature autocovariance function is approximately ten and one thousand times smaller than that of the scintillation and the wavefront slope, respectively. Thus, a significant enhancement of the attainable altitude resolution of turbulence profiles is expected from the spatio-angular autocovariance of the curvature. The curvature autocovariance amplitude is proportional to C_n² (h) and also depends on the turbulence altitude h and on the turbulence inner scale l₀. A simple procedure disentangles those dependencies and leads to C_n² (h) and also to the inner scale profile l₀(h).

Laser-based adaptive optics telemetry contains information about the atmospheric vertical profiles of turbulence strength (C²_n), outer scale (L₀) and wind speeds. Various techniques in the literature already process laser-based Shack-Hartmann telemetry and estimate the profiles out of cross-covariance maps from the slopes data. Building local derivative estimates out of the data (i.e. curvatures or even higher-order derivative estimates) is a possible mean to remove the large uncertainties existing on low-order modes in laser-based systems. The present study analyses this filtering strategies in a unified formalism. The modified shapes of the cross-covariance peaks are studied and compared. It explains how the sensitivity to the outer scale is strongly reduced by using such higher- order derivative estimates than slopes. The sharpened covariance peaks also simplify the layer detection problem in atmospheric profiling and may improve vertical resolution of SLODAR-based techniques. As a first application of this analysis, an automated algorithm for turbulence profiling is presented with results on simulated data and also on on-sky registered data from the Adaptive Optics Facility at Paranal Observatory.

Early adaptive optics (AO) systems were designed with knowledge of a site’s distribution of Fried parameter (r0) and Greenwood time delay (τ0) values. Recent systems have leveraged additional knowledge of the distribution of turbulence with altitude. We present measurements of the atmosphere above Maunakea, Hawaii and how the temporal properties of the turbulence relate to tomographic reconstructions. We combine archival telemetry collected by ‘imaka—a ground layer AO (GLAO) system on the UH88” telescope—with data from the local weather towers, weather forecasting models, and weather balloon launches, to study how frequently one can map a turbulent layer’s wind vector to its altitude. Finally, we present the initial results of designing a new GLAO control system based off of these results, an approach we have named “temporal tomography.”

The forecast on a time scale of 1 or 2 hours is crucial for all kind of new generation facilities (ELTs) instrumentation supported by the adaptive optics that will be mainly operated in Service Mode. In a recent study (Masciadri et al. 2020) we have showed that we can forecast the seeing and atmospheric parameters at such short time scales using an autoregressive method achieving unprecedented model accuracies with a substantial gain with respect to forecasts performed the day before (i.e. on longer time scales) obtained with an atmospherical mesoscale model. Equally we showed a gain with respect to the method by persistence using simply real-time measurements in situ on the same short time scale (1-2 hours). The auto-regressive method makes use of the forecasts done with mesoscale atmospherical models and real-time measurements and since 2019 has been implemented in the operational forecast system ALTA Center supporting LBT observations. In this contribution we apply the same approach to the VLT site extending the method to all the main astroclimatic parameters i.e. the seeing, the wavefront coherence time, the isoplanatic angle and the ground layer fraction. We prove that such a method offers unprecedented forecast accuracies for all the astroclimatic parameters with clear gains with respect to the prediction by persistence. Preliminary calculations indicate also better accuracies than those obtained with the machine learning based approach using in situ measurements. We will apply soon such a method in an operational forecast system that we conceived for the VLT.

The optical turbulence in the Earth’s atmosphere is detrimental to ground-based optical astronomy. it is therefore critical that we are able to model and forecast realistic atmospheric optical turbulence conditions for observatory site selection, instrument development, instrument performance validation and queue scheduling, to maximise observatory scientific output. Here, we present global maps of optical turbulence strength and associated parameters (Fried parameter, isoplanatic angle, coherence time and Rytov variance / scintillation index), from a turbulence forecasting tool. These maps can be used by the community to understand the expected performance of optical systems anywhere in the world, day and night. These maps also demonstrate that optical turbulence can be modelled and visualised in the same manner as other aspects of the Earth’s weather system such as wind, rain or temperature, opening the door for more advanced turbulence forecasting functionality.

Image quality is sensitive to temperature fluctuations on the optical path, even if these are not fully developed turbulence. Thus, it’s crucial to control the thermal environment, be it on a test bench in the laboratory, in instruments (e.g., entrance windows, near electronics), within domes and telescope structures. It is especially crucial where the beam is small (i.e., going through a focus) and the power spectrum of the refractive index can be anything from high frequencies to just tip-tilt.

We have used our optical turbulence sensor AIRFLOW to explore how a DT of a few degrees in the optical path can undo a lot of what an AO system can improve, and we are using our devices to study quantitative ways to minimize the image degradation induced by temperature fluctuations. These may include counterintuitive measures such as fans mixing the air at different temperatures, because mechanical turbulence with no DT doesn’t produce optical turbulence.

The mid-infrared (IR) regime is well suited to directly detect the thermal signatures of exoplanets in our solar neighborhood. The NEAR experiment: demonstration of high-contrast imaging (HCI) capability at ten microns, can reach sub-mJy detection sensitivity in a few hours of observation time, which is sufficient to detect a few Jupiter mass planets in nearby systems. One of the big limitations for HCI in the mid-IR is thermal sky-background. In this work, we show that precipitate water vapor (PWV) is the principal contributor to thermal sky background and science PSF quality. In the presence of high PWV, the HCI performance is significantly degraded in the background limited regime.

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.

The Keck All-Sky Precision Adaptive Optics (KAPA) system project will upgrade the Keck I AO system to enable laser tomography with a four laser guide star (LGS) asterism. This paper describes the new infrastructure which is being built for daytime calibration and testing of the KAPA tomographic algorithms.

In this article, we describe the current status of the development of TROIA ∗, a pyramid wavefront sensor based adaptive optics system designed for DAG, a new 4 m telescope located in Eastern Anatolia, Turkey. The wavefront uses a no-noise electron-multiplied CCD camera, and the deformable mirror has a large actuators density, allowing coronagraphic science in one hand, but also system optimization for low light level or bad seeing conditions thanks to the versatility of the P-WFS. We describe the optical design, the mounting and alignment procedure and our loop control concept. Closed loop results are described, showing that while there are still many issues to fix before the sky version, the system behaves as expected.

As we enter the era of TESS and JWST, instrumentation that can carry out radial velocity measurements of exoplanet systems is in high demand. We will address this demand by upgrading the UC Lick Observatory’s 2.4-meter Automated Planet Finder (APF) telescope with an adaptive optics (AO) system. The AO upgrade will be directly integrated into the APF telescope by replacing the telescope’s static secondary mirror with a 61- actuator adaptive secondary mirror (ASM) to minimize the disturbance to the spectrograph optics. This upgrade is enabled by The Netherlands Organization for Applied Scientific Research’s (TNO) large-format deformable mirror technology, which is constructed using a new style of high-efficiency hybrid-variable reluctance actuator. We outline the technical design and manufacturing plan for the proposed APF AO upgrade and simulate the improvement to the science yield using HCIpy. Our simulations predict the AO upgrade will reduce the PSF instabilities due to atmospheric turbulence, concentrating the light on the spectrograph slit by a multiplicative factor of more than two (doubling the telescope’s observing efficiency) for targets as dim as I = 14. When completed, the APF adaptive secondary mirror will be among the first pairings of an ASM with a radial velocity spectrograph and become a pathfinder for similar AO systems in telescopes of all sizes.

Facility-class high-contrast exoplanet imaging systems are currently limited by non-common path quasi-static speckles. Due to these aberrations, the raw contrast saturates after a few seconds. Several active wavefront correction techniques have been developed to remove this noise, with limited success. The NRC Canada is funding two projects, the SPIDERS pathfinder at the Subaru telescope (ETA 2023), and the CAL2 upgrade of the Gemini Planet Imager-2 (ETA 2024), to deploy a modified self-coherent camera (based on FAST) to measure the focal plane electric field, and to apply wavefront corrections in a closed-loop down to 10s of ms in a narrow band. The CAL2 project will focus on developing a facilityclass focal plane & Lyot-stop Low-order sensors using a CRED2 and a SAPHIRA-based camera, reaching up to a gain of 100x in contrast for bright stars. The SPIDERS pathfinder will have a similar configuration with the addition of an imaging Fourier transform spectrograph, allowing the acquisition of a 3.3” diagonal FOV to up to R-20,000 in the NIR to perform advanced spectral differential imaging at a high-spectral resolution to search and characterize exoplanets. These projects will serve as the foundation to develop similar systems for future ground-/space-based telescopes, and be an important step toward the development of instruments to search for life signatures in the atmosphere of exoplanets.

The European Solar Telescope (EST) is a 4.2-m telescope which has been redesigned with a fully integrated Multi-Conjugate Adaptive Optics (MCAO) into the optical path right after the EST primary mirror. The current baseline configuration considers four altitude Deformable Mirrors (DM) conjugated to 5, 9, 12 and 20 km above the telescope entrance pupil and an Adaptive Secondary Mirror (ASM) conjugated to the entrance pupil. The wavefront sensing will be performed by a set of correlation-based Shack Hartmann wavefront sensors (WFS) combining an on-axis High-Order WFS (HOWFS) to be used either in Single Conjugate AO (SCAO) to drive the ASM as well as operating simultaneously with a Multi-Directional WFS (MDWFS) to drive the MCAO. Beyond the current baseline configuration, different alternatives are currently being investigated both in the wavefront sensing strategy by evolving from a HOWFS+MDWFS into possibly a single High Order Multi Directional WFS (HOMDWFS) and/or wavefront sensors operating at different observing bands.

MAVIS will be part of the next generation of VLT instrumentation and it will include a visible imager and a spectrograph, both fed by a common Adaptive Optics Module. The AOM consists in a MCAO system, whose challenge is to provide a 30” AO-corrected FoV in the visible domain, with good performance in a 50% sky coverage at the Galactic Pole. To reach the required performance, the current AOM scheme includes the use of up to 11 reference sources at the same time (8 LGSs + 3 NGSs) to drive more than 5000 actuators, divided into 3 deformable mirrors (one of them being UT4 secondary mirror). The system also includes some auxiliary loops, that are meant to compensate for internal instabilities (including WFSs focus signal, LGS tip-tilt signal and pupil position) so to push the stability of the main AO loop and the overall performance. Here we present the Preliminary Design of the AOM, which evolved, since the previous phase, as the result of further trade-offs and optimizations. We also introduce the main calibration strategy for the loops and sub-systems, including NCPA calibration approach. Finally, we present a summary of the main results of the performance and stability analyses performed for the current design phase, in order to show compliance to the performance requirements.

ULTIMATE-Subaru is a next facility instrumentation program of the Subaru Telescope. The goal of this project is to extend the wide-field capability of the Subaru to near-infrared (NIR), by developing a wide-field ground-layer adaptive optics (GLAO) system and wide-field NIR instruments. The GLAO system will uniformly improve the image quality up to 20-arcmin field of view in diameter by correcting for the ground-layer turbulence. The expected image quality after the GLAO correction is FWHM~0".2 in K-band under moderate seeing conditions. In this presentation, we present preliminary design overview of the GLAO system at the Cassegrain focus, which consist of an Adaptive Secondary Mirror, NGS and LGS wavefront sensor system, a laser guide star facility, and control system. We also present the prototyping activities to validate the selected design of the GLAO system.

SHARK-NIR is an instrument which provides direct imaging, coronagraphic imaging, dual band imaging and low resolution spectroscopy in Y, J and H bands, taking advantage of the outstanding performance of the Large Binocular Telescope AO systems. Binocular observations will be provided used in combination with SHARK-VIS (operating in V band) and LMIRCam of LBTI (operating from K to M bands), in a way to exploit coronagraphic simultaneous observations in three different wavelengths.

A wide variety of coronagraphic techniques have been implemented in SHARK-NIR, ranging from conventional ones such as the Gaussian Lyot, to others quite robust to misalignments such as the Shaped Pupil, to eventually techniques more demanding in term of stability during the observation, as the Four Quadrant; the latter is giving in theory and simulations outstanding contrast, and it is supported in term of stability by the SHARK-NIR internal fast tip-tilt loop and local NCPA correction, which should ensure the necessary stability allowing this technique to operate at its best.

The main science case is of course exoplanets search and characterization and young stellar systems, jets and disks characterization, although the LBT AO extreme performance, allowing to reach excellent correction even at very faint magnitudes, may open to science previously difficult to be achieved, as for example AGN and QSO morphological studies.

The institutes participating to the SHARK-NIR consortium which designed and built the instrument are Istituto Nazionale di Astro Fisica (INAF, Italy), the Max Planck Institute for Astronomy (MPIA, Heidelberg, Germany) and University of Arizona/Steward Observatory (UoA/SO, Tucson, Az, USA). We report here about the SHARK-NIR status, that should achieve first light at LBT before the end of 2022.

The Adaptive Optics system of the 10-m class Gran Telescopio Canarias (GTCAO) is completing the acceptance tests in the laboratory at the Instituto de Astrofísica de Canarias, to be ready for its integration in the telescope at Roque de Los Muchachos Observatory (ORM) in 2023. The AO system has been designed with robustness and operability as its key characteristics, and will be a facility of GTC. It features a single deformable mirror (DM) with 373 actuators, conjugated to the telescope pupil, and a Shack-Hartmann wavefront sensor (WFS) with 312 subapertures, using an OCAM2 camera. The expected performance of the GTCAO system working on average atmospheric conditions and bright NGS is 65% Strehl Ratio in K-band. In this paper we present the characterization of the system and the tests that have been performed for its acceptance at the laboratory. A series of calibrations are required and methodically run to achieve its ultimate performance: flatten the DM, acquire the Interaction Matrix and the reference slopes, correct the non-common path aberrations etc. The WFS requires additional calibrations, to compensate the pupil displacement in all the 2 arcminutes patrol field of view, and to correct the atmospheric dispersion in the visible. Close loop gains and sampling frequency are adapted to the changing conditions, and lookup tables are created for that purpose. The compliance with the system specifications has been verified. After verification of the final software functionalities for telescope operation, the system will be shipped to the ORM, to be installed and aligned on the Nasmyth platform of the GTC, and to be integrated with the telescope control system.

GMagAO-X is the ExAO coronagraphic instrument for the 25.4m GMT. It is designed for a slot on the folded port of the GMT. To meet the strict ExAO fitting and servo error requirement (<90nm rms WFE), GMagAO-X must have 21,000 actuator DM capable of ≥2KHz correction speeds. To minimize wavefront/segment piston error GMagAO-X has an interferometric beam combiner on a vibration isolated table, as part of this “21,000 actuator parallel DM”. Piston errors are sensed by a Holographic Dispersed Fringe Sensor (HDFS). In addition to a coronagraph, it has a post-coronagraphic Low Order WFS (LLOWFS) to sense non-common path (NCP) errors. The LLOWFS drives a non-common path DM (NCP DM) to correct those NCP errors. GMagAO-X obtains high-contrast science and wavefront sensing in the visible and/or the NIR. Here we present our successful externally reviewed (Sept. 2021) CoDR optical-mechanical design that satisfies GMagAO-X’s top-level science requirements and is compliant with the GMT instrument requirements and only requires COTS parts.

The second phase of the ESO program aiming at developing the Deformable Mirror (DM) technology requested by the Extremely Large Telescopes’ post-focal Adaptive Optics (AO) has been kicked-off end of 2020. A development contract has been granted to ALPAO to deliver a scale-one prototype of a 64x64 actuator DM compliant with the high temporal, thermal and mechanical stability requested by open-loop AO applications. In addition, a test facility allowing the full characterization of the expected DM stability has been assembled by ALPAO and is now available; it has been recently used to assess the performance of the first GRAVITY+ DM. Additionally, a new contract is in preparation to consolidate the technology requested to deliver DMs suitable for XAO systems and high contrast imaging, and the delivery of a scale-one prototype. This paper presents the status of the open-loop DM technology development and gives details about the soon-coming XAO DM activities.

During the past years, ESO developed an ultra-fast Shack Hartman (SH) WaveFront Sensor (WFS) based on using a highspeed camera at framerates as high as 16 kHz. This WFS has been used to characterize the sub-ms spatio-temporal behaviour of Deformable Mirrors. This paper reports about the results obtained with micro voice coil actuated Deformable Mirrors. At sampling rates up to 16 kHz fast transients of the full surface can be measured allowing for detailed characterization and modelling of the mirrors’ spatio-temporal behaviour. When an optical phase step is applied to an actuator it triggers a wave travelling across the surface to the edges and then reflected. Using the fast WFS developed by ESO, it has been possible to visualize and characterize this transient phenomenon. Based on these experimental observations, different feed forward control techniques are designed and their efficiency to improve the actuators temporal behaviour and reduce the amplitude of the parasitic surface waves are compared.

The National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST) has made the transition from construction to science operations. It is currently operating with a “classical” single-conjugate Adaptive Optics (AO) system, which will be upgraded to a multi-conjugate AO (MCAO) system within the next few years. One of the key challenges for the DKIST MCAO system will be procuring a suitable Deformable Mirror (DM) to replace the current M7 flat, which is conjugate to 11.2 km.

The DM must be large in size with an elliptical clear aperture 884 by 625 mm. It must also have a high actuator density, with actuator spacings smaller than 11 mm. Additionally, it must have an actuator rise time of 100 µs and an update rate greater than 2 kHz. We have identified the surface-parallel actuated silicon carbide DMs made by Northrop Grumman’s AOA Xinetics (AOX) as a likely candidate to meet our requirements. However, there are some challenges that come with using this technology for the DKIST MCAO system. We must design our controller to avoid exciting resonant modes in the mirror. We also must minimize actuator saturation or it will become the dominant error term in our wavefront fitting error.

We discuss the advantages and disadvantages of this deformable mirror technology for astronomical imaging through the turbulent atmosphere. We use NSO’s Blur adaptive optics simulation software and the KAOS Evo 2 control software to simulate the performance of a large aperture silicon carbide DM. We also present simulation results that model the temporal error incurred by reducing the control bandwidth of the mirror’s resonant modes.

This paper describes the preliminary design of the Adaptive Secondary Mirror (ASM) for the European Solar Telescope (EST), as designed by TNO. This ASM will contain 1950 actuators over an optical aperture of Ø80cm. The mirror-shell of this ASM is concave with a radius of 2.156m and has a thickness of 2.5mm. To cope with the high optical heat-load, the mirror shell will be cooled actively by means of conduction through a small (0.3mm) airgap between the mirror shell and the cooled SiC supporting structure. One of the unique characteristics of this ASM are the highly efficient actuators by TNO, delivering 30N Peak-to-Valley of linear force range within a packaging of Ø15x40mm. These actuators are based on the proven electromagnetic actuation principle by TNO but have been significantly redesigned to improve manufacturability and integration. The actuators are interfaced to the mirror shell via a stiff carbon fiber strut assembly and are designed to be replaceable during off-telescope maintenance. For overall alignment of the ASM a hexapod is used, while a faster tip-tilt stage is used to compensate for tip-tilt disturbances up to 20Hz bandwidth. The optical performance of the ASM under various environmental conditions has been extensively studied with Finite-Element-Analysis. To verify the performances of the actuator and the cooling systems, an actuator and thermal- breadboard are being constructed.

We describe the current plans for developing an adaptive secondary mirror-based (ASM) adaptive optics (AO) system for WMKO. An ASM allows for the integration of AO into the telescope itself, broadening use of AO to include wide-field enhanced seeing, high contrast observations, and enabling future multi-conjugate upgrades. Such a system has the potential for enhancing a range of science objectives, improving the performance of both existing and future instrumentation at Keck. We describe a system level ASM-AO concept based on hybrid variable reluctance actuators, developed by TNO that simplifies the implementation of ASM’s.

To directly image and characterize exoplanets, many developments of high-contrast imaging (HCI) systems are ongoing for current ground-based telescopes as well as future extremely large telescopes and space-based telescopes. Despite recent developments in HCI, the contrast of the HCI systems is limited by non-common path aberrations (NCPAs) and residual errors of the adaptive optics (AO) system. In order to overcome these limitations, HCI systems need focal plane wavefront sensing and control (FPWFS&C) techniques.

We present the implementation of two FPWFS&C techniques, electric field conjugation (EFC) and spatial linear dark field control (LDFC), on the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument. First, we generate a half-dark hole in the focal plane image using EFC. Once the bright field and dark field (dark hole) have been established by EFC, as a second step, we deploy spatial LDFC to maintain the contrast of the half-dark hole generated by EFC. We could also use EFC to preserve the contrast of the dark hole, but it requires field modulation, which interferes with the science image acquisition. Because of this reason, we use spatial LDFC as an alternative way to maintain the contrast without modulation.

In actual demonstrations, we obtained a dark hole contrast of ∼2×10⁻⁷ with a classical Lyot coronagraph of 114 mas diameter, at a 1550 nm wavelength using EFC. This result is the first EFC implementation and the deepest contrast obtained on the SCExAO testbed. Using spatial LDFC, we also ideally removed focal plane speckles generated by static phase error and restored the initial contrast. Our results provide a promising path forward to generating the high-contrast dark hole using EFC and stabilizing the contrast of the dark hole without interrupting the science acquisition using spatial LDFC.

In order to detect low mass and mature planets inwards of approximately 5 AU, future direct imaging instruments will require precision wavefront control that operates at relatively high speed. The self-coherent camera (SCC) is a promising technique for measuring the wavefront from science images at the focal plane. We present here results from NRC’s NEW-EARTH lab testing of the Fast Atmospheric SCC Technique, a variant of the SCC and its integration with a Lyot-stop Low-Order Wavefront Sensor. We demonstrate correction of quasi-static speckles in a half dark hole reaching raw 1σ contrasts on the order of 5 × 10⁻⁷ at 10 λ/D. We also present a simplified process for extracting measurements and/or DM commands from SCC images using a single matrixvector multiply. This testing and development are important steps on the way to the upcoming Subaru Pathfinder Instrument for Detection of Exoplanets and Removal of Speckles and the Gemini Planet Imager’s CAL2 upgrade.

Extreme adaptive optics (ExAO) systems require high spatial and temporal sampling of wavefronts to optimize performance, and as a result, require large detectors for the wavefront sensor (WFS). We present a testbed demonstration of a three-sided pyramid wavefront sensor (3PWFS) as an alternative to the conventional four-sided pyramid wavefront sensor (4PWFS) for Giant Segmented Mirror Telescope ExAO applications. The 3PWFS is less sensitive to read noise than the 4PWFS because it uses fewer detector pixels. We describe the design of the Comprehensive Adaptive Optics and Coronagraph Test Instrument (CACTI). An experiment was performed on CACTI to determine the relative performance of the 3PWFS to the 4PWFS in varying strengths of turbulence using both the Raw Intensity and Slopes Map signal processing methods. We found that the performance of the two WFS is comparable if modal loop gains are tuned.

ELT-HARMONI is the first light visible and near-IR integral field spectrograph (IFS) for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews.

The High Contrast Module (HCM) will allow HARMONI to perform direct imaging and spectral analysis of exoplanets up to 10⁶ times fainter than their host star. Quasi-static aberrations are a limiting factor and must be calibrated as close as possible to the focal plane masks to reach the specified contrast. A Zernike sensor for Extremely Low-level Differential Aberrations (ZELDA) will be used in real-time and closed-loop operation at 0.1Hz frequency for this purpose. Unlike a Shack-Hartmann, the ZELDA wavefront sensor is sensitive to Island and low-wind effects. The ZELDA sensor has already been tested on VLT-SPHERE¹ and will be used in other instruments. Our objective is to adapt this sensor to the specific case of HARMONI.

A ZELDA prototype is being both simulated and experimentally tested at IPAG. Its nanometric precision has first been checked in 2020 in the case of slowly evolving, small wavefront errors, and without dispersion nor turbulence residuals. On this experimental basis, we address the performance of the sensor under realistic operational conditions including residuals, mis-centring, dispersion, sensitivity, etc. Atmospheric refraction residuals were introduced by the use of a prism, and turbulence was introduced by a spatial light modulator which is also used to minimise wavefront residuals in a closed loop in the observing conditions expected with HARMONI.

We describe new results obtained with the integrated Mach-Zehnder (iMZ) self referenced wavefront sensor (WFS) allowing to extract independently phase and amplitude from intensity variations in the pupil images produced by the interferometer. This kind of wavefront sensor meets extreme adaptive optics requirements, high speed (1 kHz) and high accuracy (< 10 nm at 5-10 cm spatial scale), as well as the reconstruction of phasing errors on segmented telescopes and scintillation measurements. In this paper we present the calibration method we have developed and validated experimentally to accurately extract the phase and the amplitude of the wavefront from the Mach-Zehnder signal, using several diversities in the phase patterns. We also present a new phase modulation method which combined with an unwrapping algorithm increases the dynamical range of the wavefront sensor up to several microns, otherwise limited to ± lambda/4 without these new strategies. Numerical simulations of the Mach-Zehnder performances for various turbulence phase will be presented to address the ultimate sensor accuracy. We will also report on our latest laboratory calibration results, using a deformable mirror and a spatial light modulator to introduce the required phase modulations.

Inner working angle is a key parameter for enabling scientific discovery in direct exoplanet imaging and characterization. Approaches to improving the inner working angle to reach the diffraction limit center on the sensing and control of wavefront errors, starlight suppression via coronagraphy, and differential techniques applied in post-processing. These approaches are ultimately limited by the shot noise of the residual starlight, placing a premium on the ability of the adaptive optics system to sense and control wavefront errors so that the coronagraph can effectively suppress starlight reaching the science focal plane. Photonic lanterns are attractive for use in the science focal plane because of their ability to spatially filter light using a finite basis of accepted modes and effectively couple the results to diffraction-limited spectrometers, providing a compact and cost-effective means to implement post-processing based on spectral diversity. We aim to characterize the ability of photonic lanterns to serve as focal-plane wavefront sensors, allowing the adaptive optics system to control aberrations affecting the science focal plane and reject additional stellar photon noise. By serving as focal-plane wavefront sensors, photonic lanterns can improve sensitivity to exoplanets through both direct and coronagraphic observations. We have studied the sensing capabilities of photonic lanterns in the linear and quadratic regimes with analytical and numerical treatments for different lantern geometries (including non-mode-selective, mode-selective, and hybrid geometries) as a function of port number. In this presentation we report on the sensitivity of such lanterns and comment on the relative suitability and sensitivity impacts of different lantern geometries for focal-plane wavefront sensing.

Ground-based high contrast imaging (HCI) and extreme adaptive optics (AO) technologies have advanced to the point of enabling direct detections of gas-giant exoplanets orbiting beyond the snow lines around nearby young star systems. However, leftover wavefront errors using current HCI and AO technologies, realized as “speckles” in the coronagraphic science image, still limit HCI instrument sensitivities to detecting and characterizing lowermass, closer-in, and/or older/colder exoplanetary systems. Improving the performance of AO wavefront sensors (WFSs) and control techniques is critical to improving such HCI instrument sensitivity. Here we present three different ongoing wavefront sensing and control project developments on the Santa cruz Extreme AO Laboratory (SEAL) testbed: (1) “multi-WFS single congugate AO (SCAO)” using the Fast Atmospheric Self-coherent camera (SCC) Technique (FAST) and a Shack Hartmann WFS, (2) pupil chopping for focal plane wavefront sensing, first with an external amplitude modulator and then with the DM as a phase-only modulator, and (3) a laboratory demonstration of enhanced linearity with the non-modulated bright Pyramid WFS (PWFS) compared to the regular PWFS. All three topics share a common theme of multi-WFS SCAO and/or second stage AO, presenting opportunities and applications to further investigate these techniques in the future.

Advances in the field of deep learning have motivated a flurry of research into the application of neural networks to wavefront sensing for adaptive optics. This paper gives an overview of current research in this area, highlighting new methods in deep learning that wavefront sensing stands to improve from. Finally we discuss future endeavours and speculate on how deep learning is expected to impact the field of wavefront sensing.

For a solar adaptive optics system equipped with a Shack-Hartmann wavefront sensor, the local wavefront slopes are measured from the displacements of the images produced by the sub-pupils of the sensor with respect to a given reference image. Measuring these displacements is challenging because of the very low contrast (at most a few percent) of the structures at the Sun surface. Additional difficulties arise from the fact that these structures evolve in time and are slightly distorted in each sub-image. In this contribution, we describe a novel approach to process the images of a solar wavefront sensor which jointly estimates the wavefront slopes, their noise covariance matrix, and the reference image. Spatio-temporal constraints are imposed on the reference image to regularize the problem and stabilize the global tip-tilt. Automatically tuned correction factors are introduced to account for the scintillation and the local distortions. Our method yields a sufficient statistic which enables an optimal wavefront reconstruction. We propose an alternating strategy to quickly solve the joint estimation problem. Special attention has been paid to make the numerical algorithm usable in real-time. Our method is implemented in the adaptive optics system of the THEMIS solar telescope equipped with a 10 × 10 Shack-Hartmann wavefront sensor delivering 400 × 400 pixel images at 1kHz. On a single CPU core, the Julia version of our algorithm provides the measurements with 90μs of latency after the image acquisition and takes an additional 200µs to update the reference image.

Currently, astronomical wavefront sensor (WFS) are optimized for two types of sources: natural guide stars (NGS) using an unresolved star as the reference or laser guide stars (LGS) with a large resolved beacon. In the former case, the coherent approximation is valid, while in the latter case, the incoherent approximation can be applied; we examine cases where neither approximation is valid or the partially coherent case. To date, there has been limited research on optimizing a WFS design for a partially coherent beacon, though there are at least two important applications: uplink corrected laser beacons and artificially induced partial coherence in modulated pyramid designs. Using Hopkins' formula1 we have derived an approximate expression for the Fisher information matrix (FIM) for any wavefront sensor design using Fourier plane filtering2 with a particular emphasis on the pyramid and Zernike WFS. From this expression we show that degradation in WFS sensitivity is primarily due to the combining of incoherent pupil point pairs. The expression also gives rise to an alternative method for modeling WFS in the partially coherent regime using the magnitude of the complex coherence factor and the WFS's coherent impulse response (CIR) to approximate the detector output. We explore two methods for optimizing WFS sensitivity with a partially coherent beacon: pupil segmentation and impulse response engineering. In the former case, the pupil is subdivided via to match the coherence area of the source and a separate coherent wavefront sensing technique is used to retrieve higher order modes in each subaperture. The latter approach optimizes the CIR of a WFS to limit the spread of light to the coherence area of the source. The effectiveness of these methods is explored through wave-optic simulation, using both the newly developed CIR method and the more standard fast Fourier transform (FFT) approach. The simulation results are also compared to measurements from a bench-level adaptive optics (AO) system using a novel software-defined WFS with two spatial light modulators (SLM) at the pupil plane and Fourier plane respectively to allow for rapid configuration of multiple WFS designs without the need for hardware changes. Bench-level measurements of the WFS sensitivity to photon noise are presented to further validate the theoretical and simulation predictions for optimal wavefront sensing with partially coherent beacons.

We develop and evaluate a new approach to phase estimation for observational astronomy that can be used for accurate point spread function reconstruction. Phase estimation is required where a terrestrial observatory uses an Adaptive Optics (AO) system to assist astronomers in acquiring sharp, high-contrast images of faint and distant objects. Our approach is to train a conditional adversarial artificial neural network architecture to predict phase using the wavefront sensor data from a closed-loop AO system. We present a detailed simulation study under different turbulent conditions, using the retrieved residual phase to obtain the point spread function of the simulated instrument. Compared to the state-of-the-art model-based approach in astronomy, our approach is not explicitly limited by modelling assumptions—e.g. independence between terms, such as bandwidth and anisoplanatism—and is conceptually simple and flexible. We use the open source COMPASS tool for end-to-end simulations. On key quality metrics, specifically the Strehl ratio and Halo distribution in our application domain, our approach achieves results better than the model-based baseline.

Selected for the next generation of adaptive optics (AO) systems, the pyramid wavefront sensor (PWFS) is recognised for its closed AO loop performance. As new technologies are emerging, it is necessary to explore new methods to improve it. Microwave Kinetic Inductance Detectors (MKID) are photon-counting devices that measure the arrival time and energy of each incident photon, providing new capabilities over existing detectors and significant AO performance benefits. After developing a multi-wavelength PWFS simulation, we study the benefits of using an energy sensitive detector, analyse the PWFS performance according to wavelength and explore the possibility of using fainter natural guide stars by widening the bandpass of the wavefront sensor.