Jean-Pierre Véran

MORFEO (Multi-conjugate adaptive Optics Relay For ELT Observations) is the post-focal adaptive optics module for the ESO Extremely Large Telescope (ELT). The instrument provides MCAO correction for two instruments: MICADO and HARMONI. The TAC (Test and Alignment Camera) is a piece of equipment that will be installed inside the MES (MICADO Emulating Structure), under the LOR (Low Order and Reference Wavefront Sensor): its main function is to simulate and verify all the requirements regarding the interface between MORFEO and MICADO in the Bologna Integration Hall, before the whole system is sent to the ELT in Chile. The TAC is subdivided into a Stage system, equipped with three linear stages – one for each axis – to precisely control the position of the assembly in space, and a Camera system, an Aluminium plate housing sensors and the necessary opto-mechanics. This paper focuses on the optomechanical design of the TAC, presenting how challenges were overcome and the choice of equipment.

Astronomical observations requiring extremely high angular resolution necessitate advanced adaptive optics (AO) systems to overcome blurring caused by the atmosphere. In addition to obtaining much sharper point-spread functions (PSFs) with these systems, it is beneficial to be able to characterize the behaviour of the resulting PSF across time and wavelength. We have installed a commercially-available Single-photon avalanche diode (SPAD) array on the focal plane of the REVOLT AO testbench at the Dominion Astrophysical Observatory, allowing us to observe the visible PSF of the system at rates up to 96 kHz. This provides a time-resolved view of the PSF at ∼100 times the frequency of the AO system itself. We use this detector to analyze the high-frequency behaviour of the PSF of the AO system, including residual tip/tilt and deformable mirror response. We also explore the performance of AO-assisted lucky imaging, in which we average together only the frames which result in the best image quality. We find that high-framerate imaging can significantly improve the PSF beyond the native capabilities of the AO system.

The ESO Extremely Large Telescope (ELT) will offer unprecedented sensitivity and resolution in the near infrared, marking a new era for ground-based astronomy. Among its key imaging instruments is the multiconjugate adaptive optics relay for ELT observations (MORFEO) coupled with multi-adaptive optics camera for deep observations (MICADO). MORFEO, formerly known as MAORY, is the largest astronomical adaptive optics (AO) system ever designed. It features 12 wavefront sensors and three deformable mirrors, for a total of over 20,000 subapertures and over 6000 actuators. MORFEO represents one of the greatest upcoming challenges in the field of astronomical AO. Although the design builds upon the heritage of previous AO systems, several architectural choices are entirely new, driven by the unique scale and requirements of this instrument. One of the main challenges is delivering high and uniform wavefront correction across the MICADO field of view. To meet this goal, the MORFEO control strategy adopts a specific approach: sodium laser guide stars are used to sense modes above focus only because differences in beacon altitude can introduce significant aberrations. Natural guide stars are instead employed to measure and correct for tip, tilt, plate scale variations, and field-averaged focus. In this work, we present the MORFEO control strategy and provide performance estimates across different observing scenarios.

For natural guide star adaptive optics (AO) systems, pyramid wavefront sensors (PWFSs) can provide a significant increase in sensitivity over the traditional Shack–Hartmann but at the cost of a reduced linear range. When using a linear reconstructor, nonlinearities result in wavefront estimation errors, which can have a significant impact on the image quality delivered by the AO system. We simulate a wavefront passing through a PWFS under varying observing conditions to explore the possibility of using a nonlinear machine learning model to estimate wavefront errors and compare with a linear reconstruction. We find significant potential improvements in delivered image quality even with computationally simple models, underscoring the need for further investigation of this approach.

Image displacement pixel processing for laser guide star (LGS) Shack–Hartmann wavefront sensors (WFS) is often based upon a center of gravity with thresholding [thresholded CoG (tCoG)] algorithm. This method yields a nearly linear response to the sub-aperture wavefront gradient, but suffers from zero-point biases due to sodium profile variability and the resulting changes in the shape of the LGS sub-aperture images. This effect interacts with additional biases due to the image truncation caused by the limited field of view of the WFS sub-apertures, as well as from WFS non-common path aberration (NCPA). Natural guide star (NGS) truth wavefront sensors (TWFS) have been proposed to correct for the resulting aberrations in the reconstructed wave-front, and multiple such TWFS would be required to control anisoplanatism effects when there are multiple LGS. We describe a novel algorithm that estimates the sodium profile from time averaged sub-aperture images of one or multiple LGS using a system imaging model. This estimate can then be used to correct for the zero-point bias by adjusting the tCoG reference vector. This eliminates the need for an NGS TWFS to detect sodium profile induced aberrations, and a single TWFS with faint NGS would then be sufficient to monitor any variations in NCPA if needed, which greatly improves the sky coverage. The reconstructed sodium profile can also be used to build constrained matched filters, a noise-optimal alternative to tCoG that requires accurate knowledge of the sub-aperture LGS images and their spatial derivatives (and has yet to be demonstrated on sky). This new sodium profile reconstruction algorithm consequently eliminates the need for dithering LGS spots on sky to determine these derivatives, which greatly simplifies the implementation of matched filtering and also provides better performance. All of the necessary sodium profile estimation, bias computations, and matched filter optimizations can be done with a modern CPU (e.g., Intel Core i7-11700) at around a 0.1-Hz update rate as a background process for the real time controller. Our simulations of this new method are for center launch LGS, but we are confident the profile estimation algorithm will work equally well if not better for side launch LGS, even when there is increased image truncation.

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 side-launched 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 20x20 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. GNAO also includes the development of a new Real Time Controller, a new GNAO Facility System Controller and finally the development of a new AO Bench. We present in this paper an overview of the GNAO facility and provide a status update of each product.

We used telemetry data from the Gemini North ALTAIR adaptive optics system to investigate how well the commands for wavefront correction (both tip/tilt and high-order turbulence) can be forecasted to reduce lag error (due to wavefront sensor averaging and computational delays) and improve delivered image quality. We showed that a high level of reduction (∼5 for tip-tilt and ∼2 for high-order modes) in the RMS wavefront error was achieved using a “forecasting filter” based on a linear autoregressive model with only a few coefficients (∼30 for tip-tilt and ∼5 for high-order modes) to complement the existing integral servo-controller. Updating this filter to adapt to evolving observing conditions is computationally inexpensive and requires <10 s of telemetry data. We also used several machine learning models (long-short term memory and dilated convolutional models) to evaluate whether further improvements could be achieved with a more sophisticated nonlinear model. Our attempts showed no perceptible improvements over linear autoregressive predictions, even for large lags in which residuals from the linear models are high, suggesting that nonlinear wavefront distortions for ALTAIR at the Gemini North telescope may not be forecasted with the current setup.

The adaptive optics systems of future Extremely Large Telescopes (ELTs) will be assisted with laser guide stars (LGS) which will be created in the sodium layer at a height of ≈90 km above the telescopes. In a Shack–Hartmann wavefront sensor, the long elongation of LGS spots on the sub-pupils far apart from the laser beam axis constraints the design of the wavefront sensor (WFS) which must be able to fully sample the elongated spots without undersampling the non-elongated spots. To fulfill these requirements, a newly released large complementary metal oxide semiconductor sensor with 1100 × 1600 pixels and 9 μm pixel pitch could be employed. Here, we report on the characterization of such a sensor in terms of noise and linearity, and we evaluate its performance for wavefront sensing based on the spot centroid variations. We then illustrate how this new detector can be integrated into a full LGS WFS for both the European Southern Observatory’s ELT and the Thirty Meter Telescope.

Narrow Field InfraRed Adaptive Optics System (NFIRAOS)1 will be the first adaptive optics (AO) system to be deployed on the Thirty Meter Telescope (TMT). NFIRAOS is a multiconjugate (MC) AO system equipped with six laser guide stars (LGSs), six LGS wavefront sensors (WFSs) made with Shack–Hartmann (SH) WFSs, two deformable mirrors (DMs), and a natural guide star (NGS) truth wavefront sensor (TWFS). NFIRAOS will provide near diffraction limited correction over 10 to 30 arcsec and partial correction over 2 arcmin in near-infrared. The unprecedented scale of NFIRAOS prompts us to build the Herzberg NFIRAOS Optical Simulator (HeNOS) bench at the National Research Council Herzberg for Astronomy and Astrophysics in Canada. The main purpose of this bench is to demonstrate the robustness and performance stability of an NFIRAOS-like MCAO system in realistic and varying conditions.

The GIRMOS instrument will bring a world-class capability to Gemini that does not currently exist or is planned for at 8-10-meter observatories. By combining the latest innovations in multi-object adaptive optics (MOAO) with quad, high-throughput integral-field spectrographs (IFS), GIRMOS’ sensitivity will be comparable to that of JWST’s IFS while offering significant multiplexing. GIRMOS will usher in a new era of large, near-infrared spectroscopic surveys that will take advantage of the superior image quality of an 8-10 meter-class telescope fed with AO. The expected gain with the inclusion of multiplexing and superior AO and spectroscopic performance is ten times other existing single-object AO-fed spectrographs. The capability to perform such observations in multi-object mode means GIRMOS will revolutionize studies in many fields in astrophysics, from observations of galaxies in the distant universe, stars in the Milky Way, the process of star formation, to the characterization of planetary atmospheres. The expected commissioning date is early 2023. In this contribution, we will present a conceptual design for the GIRMOS MOAO, simulation results, and the open loop control testing we have done to date, aimed at achieving diffraction limited performance on an 8m-class telescope in the presence of realistic turbulence. The GIRMOS spectrograph project is striving firstly for an operational instrument on Gemini that is best-in-class, and secondly, to develop and demonstrate an MOAO system as a TMT pathfinder. Central to this will be the MOAO system, which will use an object selection mechanism to patrol the 2' field of regard of the GeMS Multi-Conjugate Adaptive Optics system, correct for higher order atmospheric turbulence, and then feed the 4 IFU spectrographs. GIRMOS-MOAO will utilize deformable mirrors (DMs) with ~16x16 actuators to yield diffraction limited performance at a minimum of 50% Strehl at H-band. The instrument requires GeMS for the laser constellation and to do the wavefront sensing, as the scope and budget of GIRMOS relies on this. The MOAO system consists of deformable mirrors in each of the four spectrographs where the GeMS AO system acts as a woofer to keep the WFSs in the linear regime, while the GIRMOS MOAO system acts as a tweeter that corrects for the field specific to each IFS. Our AO simulations show that we are able to reach close to the AO performance target set by our scientific requirements with the current incarnation of GeMS (2-mirror system), and an upgrade path for GeMS in the coming years will further enhance the performance. In addition to improvements in Strehl ratios across the full GeMS field, our MOAO system will increase the overall sensitivity of the instrument ~3 times for an unresolved point source over GeMS AO alone. In the GIRMOS MOAO system behind GeMS, the DMs are used to tune the adaptive correction for a particular direction on the sky. The greatest challenge of implementing the MOAO is in tuning the open loop (OL) control, developing a system that be calibrated and run without large static errors that degrade performance. We are part-way into a development program to overcome these open loop control challenges, making use of the RAVEN test bed (Lardiere et al., 2014) at the University of Victoria, a previous MOAO pathfinder experiment that was commissioned on the Subaru telescope in 2014. To allow this significant infrastructure to be reused for this purpose, we require a new larger lenslet array and DM than currently implemented in RAVEN. These changes will allow us to improve and develop MOAO calibration techniques that we can then build into GIRMOS. GIRMOS is a Canadian instrument recently funded by the Canada Foundation for Innovation (CFI) and provincial governments.