As of today, Laser Guide Star adaptive optics can not measure the image motion induced by atmospheric turbulence. In this paper we review one of the proposed methods, never tested: the time-delay method. We will look at its application for the 1m class CaNaPy system, for the 8m class systems and potentially for extremely large telescopes. ESO and ESA are collaborating in this R&D, creating the CaNaPy-LASCA LGS-AO facility for both, Astrophysics and Optical Communications field experiments. We present the concept, its optimal setup, the potential difficulties of the time-delay method as well as the numerical simulations results when retrieving the atmospheric tip-tilt, for different telescope diameters, including the 8m+ class telescopes.
CaNaPy is an experimental Laser Guide Star Adaptive Optics facility designed to demonstrate pre-compensation of a sodium LGS uplink beam, and to investigate wavefront sensing on the pre-compensated LGS using a Pyramid wavefront sensor. CaNaPy was installed at the 1m ESA OGS telescope at the Observatorio del Teide, Tenerife, in autumn 2023. Here we report on the commissioning phase activities followed by the first on-sky results on LGS uplink pre-compensation. CaNaPy is developed at ESO in collaboration with ESA, Durham University, IAC, INAF, and Microgate, with scientific collaborators from ANU and the RICAM institute.
The CaNaPy project pioneers a novel configuration in Visible Wavelength Laser Guide Star Adaptive Optics (LGS-AO). Collaboratively established by ESA and ESO, it hosts a 70 W CW 589nm laser, employing upward propagation pre-compensation on sodium LGS via a pyramid wavefront sensor (Py-WFS). Operating at Teide Observatory, its aim is to demonstrate the benefits of pre-compensating the LGS upward propagation path, reducing LGS spot size in the mesosphere. This enhances Sodium optical pumping effects and significantly boosts Py-WFS sensitivity. Early on-sky experiments, using Natural Guide Stars, are underway, comparing results with simulation predictions using PASSATA. These trials mark a critical milestone in advancing visible wavelength LGS-AO, promising better resolution and sensitivity with reduced laser power requirements.
Reducing the numerical precision of the AO real-time control algorithm from 64 to 32 or even 16 bits provides an easy way to speed up the computations as long as it is supported by the underlying hardware. However, at a certain point the reconstruction quality will start to suffer. The present paper focuses on the Finite Element Wavelet Hybrid Algorithm (FEWHA), which is a real-time reconstruction algorithm that can be formulated either in a matrix-free and iterative way or as a matrix-vector-multiplication (MVM). The iterative approach has advantages such as no precomputation of the inverse and on the fly parameter updates, but does not support pipelining. We will study the performance of FEWHA with varying numerical precision in simulations for a MORFEO like test setting. To this end we analyze how much the reduced precision affects the reconstruction quality and the run-time of the matrix-free as well as the matrix-based implementation.
For the AO Control of the ELT instrument METIS a two-step method has been developed. First, we reconstruct the incoming wavefront from modulated Pyramid WFS measurements, second, we project this wavefront estimation on a set of modes defined on the M4 of the ELT. Here we focus on the second step, the stable fitting step of a wavefront on modes. We introduce a regularized fitting step on M4 (and subsequently all available modes without truncation) based on the same statistical information as the wavefront reconstructor. In the context of the instrument METIS we gain up to 60nm RMS and a stable performance of the AO system over all seeing and flux conditions studied.
In the design process of large adaptive mirrors numerical simulations represent the first step to evaluate the system design compliance in terms of performance, stability and robustness. To this end an efficient and accurate digital twin is required, which represents the deformable mirror and consists of complex physical models. For the next generation of Extremely Large Telescopes increased system dimensions and increased bandwidths lead to the need of modeling not only the deformable mirror alone, but also all the system supporting structure or even the full telescope. We present our high fidelity digital twin, which allows to perform the simulations within an acceptable amount of time and computational resources. The control strategy of the adaptive mirror is based on a mix between feedforward (FF) and feedback (FB) contributions. In this context optimized control parameters are important to improve both the system disturbance rejection and tracking performance. We analyze the feasibility of our digital twin via high fidelity simulations for the P72 prototype of the adaptive mirror of the Giant Magellan Telescope.
In this paper we speak about the double-axicon unit built for the CaNaPy instrument, the LGS-AO backbone of the ESA ALASCA TRL6 facility, to demonstrate Optical Feeder Links for Satellite Communications in 2023 using Laser Guide Star Adaptive Optics technologies. The ALASCA system will co-propagate a guidestar laser (λ = 589 nm) and an infrared laser (λ = 1075 nm), using the monostatic approach through the entire 1-m Optical Ground Station (OGS) at Teide Observatory, Canary Islands (Spain). Provisions have been made to use either the full aperture or a section of the OGS primary mirror. The OGS telescope secondary mirror would introduce 30% central vignetting losses on the uplink laser beams. In order to minimise the losses, a double-axicon module shapes the gaussian beam as an annulus, thus optimises the laser profile to match the telescope pupil and nulls the losses, achieving the most efficient coupling to the OGS telescope. We present the CaNaPy axicon module design and analysis for the 589-nm laser as well as the ALASCA axicon module design for the OFL; we describe the tests done and the gain achieved in power transmission when shaping the laser compared to propagating a conventional Gaussian beam through a telescope with a non-negligible central obstruction.
The Multi-conjugate Adaptive Optics RelaY (MAORY) is one of the key Adaptive Optics (AO) systems on the Extremely Large Telescope (ELT). MAORY aims to achieve a good wavefront correction over a large field of view, which involves a tomographic estimation of the 3D atmospheric wavefront disturbance. Mathematically, the reconstruction of turbulent layers in the atmosphere is severely ill-posed, hence, it limits the achievable reconstruction accuracy. Moreover, the reconstruction has to be performed in real-time at a few hundred to one thousand Hertz frame rates. In this talk we focus on the iterative Finite Element Wavelet Hybrid Algorithm (FEWHA). The key feature of FEWHA is a matrix-free representation of all underlying operators, which makes the algorithm fast and enables on the fly parameter updates. We show the performance of the algorithm regarding reconstruction quality and run-time for the MAORY instrument via numerical simulations.
The Multi-conjugate Adaptive Optics RelaY (MAORY) is one of the key adaptive optics (AO) systems on the European Southern Observatory’s Extremely Large Telescope. MAORY aims to achieve good wavefront correction over a large field of view, which involves a tomographic estimation of the three-dimensional atmospheric wavefront disturbance. Mathematically, the reconstruction of turbulent layers in the atmosphere is severely ill-posed, hence, limits the achievable reconstruction accuracy. Moreover, the reconstruction has to be performed in real time at a few hundred to one thousand hertz frame rates. Huge amounts of data have to be processed and thousands of actuators of the deformable mirrors have to be controlled by elaborated algorithms. Even with extensive parallelization and pipelining, direct solvers, such as the matrix vector multiplication method, are extremely demanding. Thus, research in recent years shifted into the direction of iterative methods. We focus on the iterative finite-element wavelet hybrid algorithm (FEWHA). The key feature of FEWHA is a matrix-free representation of all operators involved, which makes the algorithm fast and enables on-the-fly system updates whenever parameters at the telescope or in the atmosphere change. We provide a performance analysis of the method regarding quality and run-time for the MAORY instrument using the AO software package COMPASS.
The new generation of ground-based extremely large telescopes rely on adaptive optics (AO). Many AO systems require the reconstruction of the turbulence profile, which is called atmospheric tomography. Due to the growth of telescope sizes the computational load for this problem is increasing drastically. Thus, the collaboration of state-of-the-art real-time hardware with an efficient solver that take advantage of the available hardware resources is of great importance. In this talk, we look at an iterative approach called FEWHA and its adaption to perform best on real-time hardware. We conclude our talk with a comparison between FEWHA and the frequently used MVM within the framework of MAORY.
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