In the past decade the study of exoplanet atmospheres at high-spectral resolution, via transmission/emission spectroscopy and cross-correlation techniques for atomic/molecular mapping, has become a powerful and consolidated methodology. The current limitation is the signal-to-noise ratio that one can obtain during a planetary transit, which is in turn ultimately limited by telescope size. This limitation will be overcome by ANDES, an optical and near-infrared high-resolution spectrograph for the Extremely Large Telescope, which is currently in Phase B development. ANDES will be a powerful transformational instrument for exoplanet science. It will enable the study of giant planet atmospheres, allowing not only an exquisite determination of atmospheric composition, but also the study of isotopic compositions, dynamics and weather patterns, mapping the planetary atmospheres and probing atmospheric formation and evolution models. The unprecedented angular resolution of ANDES, will also allow us to explore the initial conditions in which planets form in proto-planetary disks. The main science case of ANDES, however, is the study of small, rocky exoplanet atmospheres, including the potential for biomarker detections, and the ability to reach this science case is driving its instrumental design. Here we discuss our simulations and the observing strategies to achieve this specific science goal. Since ANDES will be operational at the same time as NASA’s JWST and ESA’s ARIEL missions, it will provide enormous synergies in the characterization of planetary atmospheres at high and low spectral resolution. Moreover, ANDES will be able to probe for the first time the atmospheres of several giant and small planets in reflected light. In particular, we show how ANDES will be able to unlock the reflected light atmospheric signal of a golden sample of nearby non-transiting habitable zone earth-sized planets within a few tenths of nights, a scientific objective that no other currently approved astronomical facility will be able to reach.

ANDES,the high resolution spectrograph for the ELT, will work both in seeing limited mode and with Adaptive Optics (AO) correction. ANDES-SCAO is a single conjugated AO system working with natural guide stars, feeding the IFU coupled to the YJH spectrograph. The main science goal of the ANDES AO mode is the characterization of the exo-planet atmosphere in reflected light. Hence, the driving technical requirement for the AO system is the PSF contrast. The level of achieved contrast determines the number of exo-planets on which the instrument will be able to detect bio-signatures. The key challenge for the achievement of high contrast is the control of M4 petalling. Here, we present the current status of the ANDES-SCAO design, approaching the ANDES preliminary design review scheduled in fall 2024.

The Natural Guide-star Adaptive Optics (NGAO) mode of the Giant Magellan Telescope (GMT) is one of the two diffraction-limited AO modes under development by GMTO and its partner institutions. It will use the Adaptive Secondary Mirror (ASM) for wavefront correction, and a Natural Guide star Wavefront Sensor (NGWS) unit featuring two visible-light sensing channels to measure wavefront aberrations, including phasing errors between the seven segments of the GMT. The first NGWS channel features a modulated pyramid wavefront sensor (PWFS) and the second NGWS channel features a Holographic Dispersed Fringe Sensor (HDFS), which unambiguously detects segment piston errors as large as similar to 10 microns in wavefront. To test the performance of this novel wavefront sensing architecture, a prototype of the NGWS was built and integrated with the High Contrast AO Testbed (HCAT) and the MagAO-X system in the laboratories of the Center of Astronomical Adaptive Optics (CAAO) of the University of Arizona. The INAF Arcetri AO group designed and built the first NGWS channel, while GMTO designed and built the second NGWS channel in collaboration with CAAO. We report in this contribution the results of the laboratory experiments conducted over two two-week runs held in 2023 that demonstrate the capability of the NGWS to sense and correct for wavefront and phasing errors under the presence of mild atmospheric disturbances using the GMT NGAO control algorithms adapted to the testbed.

Context. With the Extremely Large Telescope (ELT) generation of telescopes come new challenges. The complexity of these telescopes' pupils creates new problems for adaptive optics (AO) that prevent the telescopes from reaching the theoretical resolutions that their size allows. In particular, the large spiders necessary to support the massive optics of these telescopes create discontinuities in the wavefront measurement. These discontinuities appear as a new phase error dubbed the "petal mode." This error is described as a differential piston between the fragment of the pupil separated by the spiders and is responsible for a strong degradation in the imaging quality, reducing the European ELT's resolution to that of a 15m telescope. Aims. The aim of this paper is to study the measurement of the petal mode by AO sensors. In particular, we want to understand why the pyramid wavefront sensor (PyWFS), the first-light wavefront sensor of any ELT-generation telescope, cannot measure this petal mode under normal conditions, and how to enable this measurement by adapting the AO control scheme and the PyWFS. Methods. To facilitate our study, we considered a simplified version of the petal mode, featuring a simpler pupil than the ELT. This allowed us to quickly simulate the properties of the petal mode and its measurement by the PyWFS. We studied specifically how a system that separates the atmospheric turbulence from the petal measurement would behave. Studying the petal mode's power spectral density, we proposed using a spatial filter to reduce the contribution of AO residuals to the benefit of petal mode contribution, eventually enabling it to be measured. Finally, we demonstrated our proposed system with end-to-end simulations. Results. A solution proposed to measure the petal mode is to use an unmodulated PyWFS (uPyWFS), but the uPyWFS does not make accurate measurements in the presence of atmospheric residuals. A spatial filtering step, consisting of a pinhole around the pyramid tip, reduces the first path residuals seen by the uPyWFS and restores its accuracy. This system was able to measure and control the petal mode during the end-to-end simulation. Conclusions. To address the petal problem, a two-path AO with a sensor dedicated to the measurement of the petal mode seems necessary. The question remains as to what could be used as the second path petalometer. Through this paper, we demonstrate that an uPyWFS can confuse the petal mode with the residuals from the first path. However, adding a spatial filter on top of said uPyWFS makes it a good petalometer candidate. This spatial filtering step makes the uPyWFS less sensitive to the first path residuals while retaining its ability to measure the petal mode.

To facilitate easy prediction and estimation of Adaptive Optics performance, we have created a fast algorithm named TipTop. This algorithm generates the expected AO Point Spread Function (PSF) for any existing AO observing mode (SCAO, LTAO, MCAO, GLAO) and any set of atmospheric conditions. Developed in Python, TipTop is based on an analytical approach, with simulations performed in the Fourier domain, enabling very fast computation times (less than a second per PSF) and efficient exploration of the extensive parameter space. TipTop can be used for several applications, from assisting in the observation preparation with the Exposure Time Calculator (ETC), to providing PSF models for post-processing. TipTop can also be used to help users in selecting the best NGSs asterism and optimizing their observation. Over the past years, the code has been intensively tested against different other simulation tools, showing very good agreements. TipTop is also currently deployed for VLT instruments, as proof of concepts in preparation of the ELT. The code is available here: https://tiptop.readthedocs.io/en/main/, and we encourage all future observers of the ELT to test it and provide feedback !

The Giant Magellan telescope adaptive optics system will use two different diffraction-limited imaging modes. One of them is the Natural Guide Star Adaptive Optics mode (NGAO). NGAO uses a 7-segment ASM to provide wavefront correction and a single natural guide star coupled with a post focal wavefront sensor called the NGWS. The NGWS has two different channels: the main one featuring a high spatial sampling pyramid sensor dedicated to the fast frame rate correction of atmospheric turbulence and the second one featuring an Holographic Dispersed Fringe Sensor dedicated to phasing correction of the seven segments of the GMT. The Arcetri AO group, in collaboration with GMTO, designed and built a prototype of the NGWS. Arcetri AO group was in charge of providing the design, fabrication and testing of the pyramid wavefront sensor channel of the NGWS prototype that replicates all aspects of optical sensitivity including optical design, camera selection and data reduction of the final NGWS unit. The NGWS prototype was fully integrated at the University of Arizona in the High Contrast Adaptive Optics Testbed (HCAT) during summer 2023 and has been tested to demonstrate its capability to keep the segments of the GMT in phase during a high-performance AO loop. The paper focuses on the aspects of the integration and tests related to the pyramid sensor.

In the past two years significant forward progress has been achieved in development of Adaptive Optics sensing and control technology needed for the observation modes of the Giant Magellan Telescope1. Most notable is the recent progress in demonstrating the accurate and stable control of segment piston in the diffraction-limited Natural Guide Star AO observation mode. Two NSF-funded testbeds have been successfully operated to validate the control algorithms for active optics, adaptive optics and segment piston in diffraction-limited observation. GMTO also built and operated wavefront sensor prototypes and integrated them with the testbeds. The testing has largely validated the wavefront sensor designs and has retired much of the fabrication and assembly risks. In parallel with the hardware demonstrations, significant progress has been achieved in both NGAO and LTAO control simulations verifying compliance with the required performance in each of these observation modes and thereby supporting the image quality budgets. In the area of design the GMTO Telescope Metrology Subsytem has passed its Preliminary Design Review and the conceptual design of the Adaptive Optics Test Camera has been completed. Finally, a Delta Preliminary Design phase for the LTAO hardware has begun.

TIPTOP is a python library that is able to quickly compute Point Spread Functions (PSF) of any kind of Adaptive Optics systems. This library has multiple objectives: support the exposure time calculators of future VLT and ELT instruments, support adaptive optics systems design activities, be part of PSF reconstruction pipelines and support the selection of the best asterism of natural guide stars for observation preparation. Here we report one of the last improvements of TIPTOP: the introduction of the error given by a single conjugated laser, commonly known as the cone effect. The Cone effect was not introduced before because it is challenging due to the non-stationarity of the phase. Laser guide stars are at a finite distance with respect to the telescope and probe beam accepted by the wavefront sensor has the shape of a cone. Given a single spatial frequency in an atmospheric layer, the cone effect arises from the apparent magnification or stretching of this frequency when it reaches the wavefront sensor. The magnification effect leads to an incorrect estimation of the spatial frequency. Therefore, we estimate the residual power by calculating the difference between two sinusoids with different periods: the nominal one and the magnified one. Replicating this for each spatial frequency we obtain the power spectrum associated with the cone effect. We compare this estimation with the one given by end-to-end simulation and we present how we plan to validate this with on-sky data.

The Giant Magellan Telescope (GMT) Adaptive Optics (AO) systems feature a single conjugate natural guide star based AO system using the 7 deformable secondaries and a post focal wavefront sensor named NGWS (Natural Guide star Wavefront Sensor). The NGWS has two different channels: one featuring a high spatial sampling pyramid sensor dedicated to the fast frame rate correction of atmospheric turbulence and a second dedicated to the correct phasing of the 7 segments of the GMT telescope. The Arcetri AO group in collaboration with the GMT Organization (GMTO) and the University of Arizona (UA) is in charge of providing the design, fabrication and test of a prototype of the NGWS system that shall replicate all aspects of optical sensitivity including optical design, camera selection and data reduction. The prototype design starts from the baseline design for the NGWS that was provided by the Arcetri group in 2013. The prototype project Kick-off Meeting was held on April 16th 2021 and is foreseen to reach completion 34 months later. A first set of performance tests will be performed locally in Arcetri and the final prototype performance verification will happen at UA laboratories after installation of the unit on the High Contrast AO test bench developed by the AO group of UA. This final verification is scheduled for the summer of 2023. The paper reports about the prototype development work summarizing results of numerical simulation that lead to the chosen opto-mechanical design, main features and challenges of optical design for the two sensing channels.

The Giant Magellan Telescope’s primary and deformable secondary mirror are each composed of 7 segments. The Natural Guide Star (NGS) wavefront sensor has the critical task to keep these 7 segments in phase in addition to the classical Adaptive Optics (AO) correction. The baseline defined several years ago has two pyramid wavefront sensors working in the visible. The first one is used to close the AO loop (main channel), but it is not sensitive to differential pistons that are multiples of its central wavelength (λ1), leading to segment ejections. The second pyramid, sensing at a slightly higher wavelength, is then used as a slow ”truth sensor” (2nd channel) to derive the sign of a segment ejection and correct it by steps of λ1. However, the robustness of this solution with respect to noise and turbulence conditions is not satisfying. We are now in a prototyping phase, for which the first step is to improve the baseline or find an alternative design for the 2nd channel in order to gain robustness. One of the potential solutions is LIFT, a focal-plane wavefront sensor. By making use of the sensor at two different wavelengths, it is possible to derive an unambiguous differential piston measurement. In this work, we describe our piston control strategy and show the results of end-to-end simulations comprising the full AO loop and the 2nd channel correction at the faint end of the NGS mode.

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.

We investigate the adoption of Machine Learning techniques for piston sensing in the context of segmented primary mirror telescopes by the means of numerical simulations. Considering a Natural Guide Star Wavefront Sensor, composed by one high order modes sensor plus a second sensor dedicated to the differential piston modes, we focus on the latter and tackle the problem of providing an accurate estimation for the piston modes coefficients from a defocused image of the system PSF. We consider as a baseline algorithm a customized version of LIFT (which is based on a Maximum Likelihood Estimation) and compare its performance with a Deep Neural Network (DNN) regression. After considering several DNN architectures, we designed a simple one and performed some degree of hyperparameter optimization on it to obtain the final DNN version. The code we developed is written in Python and relies on the Tensorflow4 library and its numerical backend JAX3.

The demand for higher resolution telescopes leads to segmented primary mirrors that need to be phased for operation. A phasing sensor applying a wavelength sweep technique provides a large capture range without modulating the position of individual mirror segments. This technique offers the potential to monitor the phasing state of a segmented telescope in parallel to the science observations. We evaluate the performance of the wavelength sweep technique using a Zernike phase contrast sensor for coarse phasing. Test results on a dedicated bench show 112 nm rms precision. With the help of a simulation, we explain a known error of the method and we suggest ways for improvements.

The next generation of extremely large telescopes requires the use of segmented mirrors. This technology needs specific wave front sensors to measure the alignment and phasing state. This paper compares two specific technologies for the measurement of wavefront steps between segments: a simple pin hole and a phase contrast sensor. The efficiency of each sensor will be quantified by calculating the Fisher information, first, under ideal conditions, then including the effects of sampling and atmospheric turbulence.

In the context of the segmented primary mirror of the E-ELT, the ability to measure the phasing state of neighbouring segments during day-time represents a way to mitigate the risk of potentially time consuming on-sky phasing after segment replacement. This paper presents the concept of a local phasing sensor based on simultaneous multi-wavelength shearing interferometry, as well as experimental results obtained on the ESO M1 test facility.

In the context of the segmented primary mirror of the E-ELT, the ability to measure the phasing state of neighbouring segments during day-time represents a way to mitigate the risk of potentially time consuming on-sky phasing after segment replacement. This paper presents the concept of a local phasing sensor based on simultaneous multi-wavelength shearing interferometry, as well as experimental results obtained on the ESO M1 test facility.