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.

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.

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).

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.

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 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.

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.

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.

Direct imaging of Earth-like exoplanets is one of the significant scientific drivers of the next generation of ground-based telescopes. Typically, Earth-like exoplanets are located at tiny angular separations from their host stars rendering their identification difficult. Consequently, the adaptive optics (AO) system’s control algorithm must be carefully designed to distinguish the exoplanet from the residual light produced by the host star.

A new promising avenue of research aimed at improving AO control builds on data-driven control methods such as Reinforcement Learning (RL) methods. It is an active branch of the machine learning research field, where control of a system is learned through interaction with the environment. Thus, RL can be seen as an automated approach for AO control. In particular, model-based reinforcement learning (MBRL) has been shown to cope with both temporal and misregistration errors. Similarly, it has been demonstrated to adapt to non-linear wavefront sensing while being efficient to train and execute.

The infrared low order sensor (IRLOS) upgrade project was recently launched to increase the sky coverage of GALACSI narrow-field mode (NFM).1, 2 While the baseline is to perform low-order wavefront sensing with a 2x2 Shack-Hartmann wavefront sensor (SHWFS) operating in the J+H band, a full-pupil mode was proposed to address the faintest end of the magnitude range by concentrating the photons from the full aperture in a single point spread function (PSF). In this context, we have investigated the wavefront sensing approach called the linearized focal-plane technique (LIFT). It enables the retrieval of low-order modes such as tip/tilt, defocus, astigmatism (and possibly more) from a single focal-plane PSF of a very faint natural guide star (NGS) target. LIFT is a phase diversity technique based on introducing a known amount of astigmatism into the optical path. The morphological change induced by the astigmatic shift allows encoding information about the phase aberrations into the PSF morphology.

The Gemini North Adaptive Optics (GNAO) facility is the upcoming AO facility for Gemini North providing a state-of-the-art AO system for surveys and time domain science in the era of JWST and Rubin operations.

GNAO will be optimized to feed the Gemini infrared Multi Object Spectrograph (GIRMOS). While GIRMOS is the primary science driver for defining the capabilities of GNAO, any instrument operating with an f/32 beam can be deployed using GNAO.

The GNAO project includes the development of a new laser guide star facility which will consist of four sidelaunched laser beams supporting the two primary AO modes of GNAO: a wide-field mode providing an improved image quality over natural seeing for a 2-arcminute circular field-of-view and a narrow-field mode providing near diffraction-limited performance over a 20 × 20 arcsecond square field-of-view. The GNAO wide field mode will enable GIRMOS’s multi-IFU configuration in which the science beam to each individual IFU will be additionally corrected using multi-object AO within GIRMOS. The GNAO narrow field mode will feed the GIRMOS tiled IFU configuration in which all IFUs are combined into a “super”-IFU in the center of the field.