An active wavefront sensor to make feasible adaptive optics on 100m class telescopes

ABSTRACT Layer Oriented wavefront sensors can be made with a reasonable compact detector by the adoption of several stars enlargers, increasing only locally the focal ratio on the reference stars. The main opto-mechanical requirement in this kind of device is represented by the tolerances in tip and tilt of these star enlargers, which have to be moved over the Field Of View and aligned with the reference stars. A differential tip-tilt among the star enlargers leads to a mismatch between the different pupil images related to the reference stars. This misalignment eventually translates into a blurring of the measured wavefront, reducing the sensing quality. We describe a conceptual layout for an active control of the wavefront sensor, in order to reach the best mechanical positioning of these stars enlargers. In particular we discuss an algorithm to determine the effective pupils positions by simple movements and apply the requested displacement through commercially available piezoelectric actuators, shown in a preliminary opto-mechanical design of such wavefront sensor

LOST - Layer Oriented Simulation Tool

The Layer-Oriented Simulation Tool (LOST) is a code for simulating the performance of multiconjugate adaptive optics modules that uses a layer-oriented approach. It calculates atmospheric layers as phase screens, and then calculates the phase delays caused by these screens on the wave fronts of natural guide stars through geometrical optics approximations. This simulation considers the impact of wave-front sensors on measurement phase noise when combining wave fronts optically or numerically. The LOST code is explained in a dedicated publication. It was used for the estimation of the performance of the two layer-oriented modules MAD and NIRVANA, specifically the Multiconjugate Adaptive Optics Demonstrator for the Very Large Telescope and the Near-IR-Visible Adaptive Interferometer for Astronomy for the Large Binocular Telescope

Exoplanet imaging data challenge: benchmarking the various image processing methods for exoplanet detection

The Exoplanet Imaging Data Challenge is a community-wide effort meant to offer a platform for a fair and common comparison of image processing methods designed for exoplanet direct detection. For this purpose, it gathers on a dedicated repository (Zenodo), data from several high-contrast ground-based instruments worldwide in which we injected synthetic planetary signals. The data challenge is hosted on the CodaLab competition platform, where participants can upload their results. The specifications of the data challenge are published on our website https://exoplanet-imaging-challenge.github.io/. The first phase, launched on the 1st of September 2019 and closed on the 1st of October 2020, consisted in detecting point sources in two types of common data-set in the field of high-contrast imaging: data taken in pupil-tracking mode at one wavelength (subchallenge 1, also referred to as ADI) and multispectral data taken in pupil-tracking mode (subchallenge 2, also referred to as ADI+mSDI). In this paper, we describe the approach, organisational lessons-learnt and current limitations of the data challenge, as well as preliminary results of the participants’ submissions for this first phase. In the future, we plan to provide permanent access to the standard library of data sets and metrics, in order to guide the validation and support the publications of innovative image processing algorithms dedicated to high-contrast imaging of planetary systems

E-ELT M4 adaptive unit final design and construction: a progress report

The E-ELT M4 adaptive unit is a fundamental part of the E-ELT: it provides the facility level adaptive optics correction that compensates the wavefront distortion induced by atmospheric turbulence and partially corrects the structural deformations caused by wind. The unit is based on the contactless, voice-coil technology already successfully deployed on several large adaptive mirrors, like the LBT, Magellan and VLT adaptive secondary mirrors. It features a 2.4m diameter flat mirror, controlled by 5316 actuators and divided in six segments. The reference structure is monolithic and the cophasing between the segments is guaranteed by the contactless embedded metrology. The mirror correction commands are usually transferred as modal amplitudes, that are checked by the M4 controller through a smart real-time algorithm that is capable to handle saturation effects. A large hexapod provides the fine positioning of the unit, while a rotational mechanism allows switching between the two Nasmyth foci. The unit has entered the final design and construction phase in July 2015, after an advanced preliminary design. The final design review is planned for fall 2017; thereafter, the unit will enter the construction and test phase. Acceptance in Europe after full optical calibration is planned for 2022, while the delivery to Cerro Armazones will occur in 2023. Even if the fundamental concept has remained unchanged with respect to the other contactless large deformable mirrors, the specific requirements of the E-ELT unit posed new design challenges that required very peculiar solutions. Therefore, a significant part of the design phase has been focused on the validation of the new aspects, based on analysis, numerical simulations and experimental tests. Several experimental tests have been executed on the Demonstration Prototype, which is the 222 actuators prototype developed in the frame of the advanced preliminary design. We present the main project phases, the current design status and the most relevant results achieved by the validation tests

Deformable Mirrors developments at ESO

Already several deformable mirrors are in use at Paranal and more will come in the next years. With the next generation and telescope and associated instruments, adaptive optics become an integrated part of the telescope and provide as such the first layer of image correction. The M4 E-ELT has been specified to provide a good image quality under average seeing but it is also clear that going to larger field of view or when looking for higher performance additional deformable mirrors need to be implemented in the instruments. We present here how the needs in term of performance have evolved in the last decade. After a description of the performance for the future ELT M4, a review of the parameter space will be outlined and the development plan presented

Challenges in simulating advanced control methods for AO

This paper discusses various practical problems arising in the design and simulation of predictive control methods for adaptive optics. Although there has been increased attention towards optimal prediction and control methods for AO systems, they are often tested in simplified simulation environments. The use of advanced AO simulators however, is a valuable alternative to the use of real data or laboratory experiments, as they provide both a flexible environment which is ideal for testing a new algorithm and are more accessible to non-experts. Topics that are often not explicitly discussed, such as the identification of a turbulence dynamics model from data, the use of matrix structures in AO systems to decrease the computational complexity and the implementation of Kalman filters to optimally deal with realistic noise conditions are examined. All topics discussed are illustrated by an accompanying Matlab code, which is based on the existing Matlab AO toolbox OOMAO.</p

Phase and Lyot-type coronagraphs for the High Order Testbench: prototyping and first laboratory results

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