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Multiconjugate adaptive optics (MCAO) will assist a new era of ground-based astronomical observations with the extremely large telescopes and the Very Large Telescope. High-precision relative astrometry is among the main science drivers of these systems and challenging requirements have been set for the astrometric measurements. A clear understanding of the astrometric error budget is needed and the impact of the MCAO correction has to be taken into account. In this context, we propose an analytical formulation to estimate the residual phase produced by an MCAO correction in any direction of the scientific field of view. The residual phase, computed in the temporal frequency domain, allows to consider the temporal filtering of the turbulent phase from the MCAO loop and to extract the temporal spectrum of the residuals, as well as to include other temporal effects such as the scientific integration time. The formulation is kept general and allows to consider specific frameworks by setting the telescope diameter, the turbulence profile, the guide stars constellation, the deformable mirrors configuration, the modes sensed and corrected, and the tomographic reconstruction algorithm. The formalism is presented for both a closed loop and a pseudo-open loop control. We use our results to investigate the effect of tip-tilt residuals on MCAO-assisted astrometric observations. We derive an expression for the differential tilt jitter power spectrum that also includes the dependence on the scientific exposure time. Finally, we investigate the contribution of the differential tilt jitter error on the future astrometric observations with MAVIS and MAORY.

Characterizing the PSF of adaptive optics instruments is of paramount importance both for instrument design and observation planning/optimization. Simulation software, such as PASSATA, have been successfully utilized for PSF characterization in instrument design, which make use of standardized atmospheric turbulence profiles to produce PSFs that represent the typical instrument performance. In this contribution we study the feasibility of using such tool for nowcast application (present-time forecast), such as the characterization of an on-sky measured PSF in real observations. Specifically we will analyze the performance of the simulation software in characterizing the real-time PSF of two different state-of-the-art SCAO adaptive optics instruments: SOUL at the LBT, and SAXO at the VLT. The study will make use of on-sky measurements of the atmospheric turbulence and compare the results of the simulations to the measured PSF figures of merit (namely the FHWM and the Strehl Ratio) retrieved from the instrument telemetry in real observations. Our main goal in this phase is to quantify the level of uncertainly of the AO simulations in reproducing real on-sky observed PSFs with an end-to-end code (PASSATA). In a successive phase we intend to use a faster analytical code (TIPTOP). This work is part of a wider study which aims to use simulation tools joint to atmospheric turbulence forecasts performed nightly to forecast in advance the PSF and support science operations of ground-based telescopes facilities. The 'PSF forecast' option might therefore be added to ALTA Center or the operational forecast system that will be implemented soon at ESO., 10 pages, 6 figures

The astronomical applications greatly benefit from the knowledge of the instrument PSF. We describe the PSF Reconstruction algorithm developed for the LBT LUCI instrument assisted by the SOUL SCAO module. The reconstruction procedure considers only synchronous wavefront sensor telemetry data and a few asynchronous calibrations. We do not compute the Optical Transfer Function and corresponding filters. We compute instead a temporal series of wavefront maps and for each of these the corresponding instantaneous PSF. We tested the algorithm both in laboratory arrangement and in the nighttime for different SOUL configurations, adapting it to the guide star magnitudes and seeing conditions. We nick-named it "BRUTE", Blind Reconstruction Using TElemetry, also recalling the one-to-one approach, one slope-to one instantaneous PSF the algorithm applies., 11 pages, 7 figures, Proceeding of the SPIE Conference 12185, Adaptive Optics Systems VIII, 1218540 (29 August 2022)

Laser Guide Star (LGS) Shack-Hartmann (SH) wavefront sensors for next generation Extremely Large Telescopes (ELTs) require low-noise, large format (about 1Mpx), fast detectors to match the need for a large number of subapertures and a good sampling of the very elongated spots. One path envisaged to fulfill this need has been the adoption of CMOS detectors with a rolling shutter read-out scheme, that allows low read-out noise and fast readout time at the cost of image distortion due to the detector rows exposed in different moments. In this work we analyze the impact of the rolling shutter read-out scheme when used for LGS SH wavefront sensing of the Multiconjugate adaptive Optic Relay For ELT Observations (MORFEO, formerly known as MAORY) for ESO ELT; in particular, we focus on the impact on the adaptive optics correction of the distortion-induced aberrations created by the rolling exposure in the case of fast varying aberrations, like the ones coming from the LGS tilt jitter due to the up-link propagation of laser beams. We show that the LGS jitter-induced aberration for MORFEO can be as large as 100nm rms and we discuss possible mitigation strategies., 8 pages, 6 figures, SPIE Astronomical Telescopes + Instrumentation, 2022, Montreal, Canada

International audience

The MCAO Assisted Visible Imager and Spectrograph (MAVIS) is a new visible instrument for ESO Very Large Telescope (VLT). Its Adaptive Optics Module (AOM) must provide extreme adaptive optics correction level at low galactic latitude and high sky coverage at the galactic pole on the FoV of 30arcsec of its 4k x 4k optical imager and on its monolithic Integral Field Unit, thanks to 3 deformable mirrors (DM), 8 Laser Guide Stars (LGS), up to 3 Natural Guide Stars (NGS) and 11 Wave Front Sensors (WFS). A careful performance estimation is required to drive the design of this module and to assess the fulfillment of the system and subsystems requirements. Here we present the work done on this topic during the last year: we updated the system parameters to account for the phase B design and for more realistic conditions, and we produced a set of results from analytical and end-to-end simulations that should give a as complete as possible view on the performance of the system., Comment: 13 pages, 16 figures, 2 tables, SPIE Astronomical Telescopes + Instrumentation, 2022, Montreal, Canada

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 ($\sim$ 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. 50$\mu$as 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 intra- and 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.

International audience; The instruments developed for the upcoming Extremely Large Telescopes (ELTs) will need efficient Adaptive Optics (AO) systems to correct the effects of the atmospheric turbulence and allow imaging at the highest angular resolution. One of the most important requirement for ELT AO-assisted instruments will be to deliver diffractionlimited images in a significant part of the sky. For that, the instruments will be equipped with Laser Guide Stars (LGSs) providing most of the information required by AO instruments. But even with LGSs, AO systems still require the use of Natural Guide Stars (NGSs) to compensate for image motion (jitter) and some low order aberrations. These NGSs are eventually limiting the fraction of the sky that can be achieved by AO systems, the so-called Sky Coverage. In this paper, we first present the sky coverage assessment methods used for HARMONI (High Angular Resolution Monolithic Optical and Near-infrared Integral field spectrograph) and MAORY/MICADO (Multi-conjugate Adaptive Optics RelaY/Multi-AO Imaging Camera for Deep Observations), that are both instruments for the Extremely Large Telescope of the European Southern Observatory (ESO). They are based on a semi-analytical description of the main contributors in the AO error budget, allowing for a fast estimation of the residual jitter. As such, these methods are well suited for statistical estimation of the sky coverage on multiple science fields, and/or to efficiently explore the system parameter space. We then compute the sky coverage of the two instruments in cosmological fields from the Cosmic Assembly Near-IR Deep Extragalactic Legacy Survey (CANDELS) catalog. The goal is to provide an insight on the possibilities given by two different types of tomographic AO systems, i. e. Laser Tomography AO (LTAO) with HARMONI and Multi-Conjugate AO (MCAO) with MAORY, on the same telescope. In particular, we show that HARMONI and MAORY/MICADO are complementary, meaning that the overall sky coverage of ESO's ELT is much improved for applications common to both systems.

Laser guide star (LGS) wave-front sensing (LGSWFS) is a key element of tomographic adaptive optics system. However, when considering Extremely Large Telescope (ELT) scales, the LGS spot elongation becomes so large that it challenges the standard recipes to design LGSWFS. For classical Shack-Hartmann wave-front sensor (SHWFS), which is the current baseline for all ELT LGS-assisted instruments, a trade-off between the pupil spatial sampling [number of sub-apertures (SAs)], the SA field-of-view (FoV) and the pixel sampling within each SA is required. For ELT scales, this trade-off is also driven by strong technical constraints, especially concerning the available detectors and in particular their number of pixels. For SHWFS, a larger field of view per SA allows mitigating the LGS spot truncation, which represents a severe loss of performance due to measurement biases. For a given number of available detectors pixels, the SA FoV is competing with the proper sampling of the LGS spots, and/or the total number of SAs. We proposed a sensitivity analysis, and we explore how these parameters impacts the final performance. In particular, we introduce the concept of super resolution, which allows one to reduce the pupil sampling per WFS and opens an opportunity to propose potential LGSWFS designs providing the best performance for ELT scales., Comment: 21 pages, 11 figures, 1 table, part of the 2022 JATIS Special Section on Extremely Large Telescopes

International audience; MAORY is the Laser Guide Star (LGS) assisted Multi Conjugated Adaptive Optics (MCAO) module of ESO's ELT where MAORY will provide a corrected field of view of 1 arcminute to its first client instrument MICADO. In the framework of the design phase B, the dimensioning of the LGS Shack-Hartmann Wave Front Sensor (WFS) has been investigated. On an ELT scale, the LGS spot truncation is severe and may lead to a potential loss of performance due to measurement noise as well as non-linearity and truncation induced bias. In this paper, we review the already known design options allowing to cope with LGS spot elongation and truncation problem. Then, we focus on MAORY and the design trade-off of a classical Shack-Hartmann WFS, addressing in particular the choice of the pixel scale and in turn the subaperture field of view. A larger field of view allows mitigating the truncation effects as long as the spot remains properly sampled, by means of extending it. Furthermore, we recall that in the case of a multi LGS WFS system, a large part of the problem can be solved thanks to the redundancy of pupil and metapupil sampling. The key lies in the proper tuning of the wavefront reconstruction, using as priors both the 3D turbulence covariance and well-tuned measurement noise and model errors. The number of reconstructed layers and the definition of their prior altitude and strength have been optimized. The WFS measurement errors are modelled by including the non-uniformity of LGS elongation across the pupil plane. The MCAO performance is evaluated both in terms of pure closed loop residuals and quasi static bias.

MAORY is one of the approved instruments for the European Extremely Large Telescope. It is an adaptive optics module, enabling high-angular resolution observations in the near infrared by real-time compensation of the wavefront distortions due to atmospheric turbulence and other disturbances such as wind action on the telescope. An overview of the instrument design is given in this paper.