Image quality and high contrast improvements on VLT/NACO

NACO is the famous and versatile diffraction limited NIR imager and spectrograph with which ESO celebrated 10 years of Adaptive Optics at the VLT. Since two years a substantial effort has been put in to understanding and fixing issues that directly affect the image quality and the high contrast performances of the instrument. Experiments to compensate the non-common-path aberrations and recover the highest possible Strehl ratios have been carried out successfully and a plan is hereafter described to perform such measurements regularly. The drift associated to pupil tracking since 2007 was fixed in October 2011. NACO is therefore even better suited for high contrast imaging and can be used with coronagraphic masks in the image plane. Some contrast measurements are shown and discussed. The work accomplished on NACO will serve as reference for the next generation instruments on the VLT, especially those working at the diffraction limit and making use of angular differential imaging (i.e. SPHERE, VISIR, possibly ERIS).Comment: 14 pages, 5 figures, SPIE 2012 Astronomical Instrumentation Proceedin

Adaptive optics telemetry standard: Design and specification of a novel data exchange format

Context. The amount of adaptive optics (AO) telemetry generated by visible/near-infrared ground-based observatories is ever greater, leading to a growing need for a standardised data exchange format to support performance analysis, AO research, and development activities that involve large-scale telemetry mining, processing, and curation.Aims. This paper introduces the Adaptive Optics Telemetry (AOT) data exchange format as a standard for sharing AO telemetry from visible/infrared ground-based observatories. AOT is based on the flexible image transport system (FITS) and aims to provide unambiguous and consistent data access across various systems and configurations, including natural and single- or multiple-laser guide-star AO systems.Methods. We designed AOT with a focus on two key use cases: atmospheric turbulence parameter estimation and point-spread function reconstruction. We prototyped and tested the design using existing AO telemetry datasets from multiple systems: single conjugate with natural and laser guide stars, tomographic systems with multi-channel wavefront sensors, and single- and multi-wavefront correctors in systems featuring either a Shack-Hartmann or Pyramid as the main wavefront sensor.Results. The AOT file structure has been thoroughly defined, with specified data fields, descriptions, data types, units, and expected dimensions. To support this format, we have developed a Python package that enables the data conversion, reading, writing, and exploration of AOT files; it has been made publicly available and is compatible with a general-purpose Python package manager. We have demonstrated the flexibility of the AOT format by packaging data from five different instruments, installed on different telescopes

The E-ELT first light spectrograph HARMONI: capabilities and modes

Trabajo presentado en SPIE Astronomical Telescopes, celebrado en San Diego (California), del 26 de junio al 1 de julio de 2016HARMONI is the E-ELT's first light visible and near-infrared integral field spectrograph. It will provide four different spatial scales, ranging from coarse spaxels of 60 × 30 mas best suited for seeing limited observations, to 4 mas spaxels that Nyquist sample the diffraction limited point spread function of the E-ELT at near-infrared wavelengths. Each spaxel scale may be combined with eleven spectral settings, that provide a range of spectral resolving powers (R 3500, 7500 and 20000) and instantaneous wavelength coverage spanning the 0.5 - 2.4 ¿m wavelength range of the instrument. In autumn 2015, the HARMONI project started the Preliminary Design Phase, following signature of the contract to design, build, test and commission the instrument, signed between the European Southern Observatory and the UK Science and Technology Facilities Council. Crucially, the contract also includes the preliminary design of the HARMONI Laser Tomographic Adaptive Optics system. The instrument's technical specifications were finalized in the period leading up to contract signature. In this paper, we report on the first activity carried out during preliminary design, defining the baseline architecture for the system, and the trade-off studies leading up to the choice of baseline

Etude des galaxies lointaines et optiques adaptatives tomographiques pour ELTs

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Transformer neural networks for closed-loop adaptive optics using nonmodulated pyramid wavefront sensors

Context. The pyramid wavefront sensor (PyWFS) provides the required sensitivity for demanding future adaptive optics (AO) instruments. However, the PyWFS is highly nonlinear and requires the use of beam modulation to successfully close an AO loop under varying atmospheric turbulence conditions. This comes at the expense of a loss in sensitivity. Aims. We trained, analyzed, and compared the use of deep neural networks (NNs) as nonlinear estimators for the nonmodulated PyWFS, identifying the most suitable NN architecture for a reliable closed-loop AO. Methods. We developed a novel training strategy for NNs that seeks to accommodate for changes in residual statistics between open and closed loops, plus the addition of noise for robustness purposes. Through simulations, we tested and compared several deep NNs from classical to new convolutional neural networks (CNNs), plus the most recent transformer neural network (TNN; global context visual transformer, GCViT), first for an open loop and then for a closed loop. By identifying and properly retraining the most adequate deep neural net, we tested its simulated performance first in an open loop and then for closing an AO loop at a variety of noise and turbulence conditions. We finally tested the trained NN ability to close a real AO loop for an optical bench. Results. Using open-loop simulated data, we observe that a TNN (GCViT) largely surpasses any CNN in estimation accuracy in a wide range of turbulence conditions. Moreover, the TNN performs better in a simulated closed loop than CNNs, avoiding estimation issues at the pupil borders. When closing the loop at strong turbulence and low noise, the TNN using nonmodulated PyWFS data is able to close the loop, similar to a PyWFS with 12λ/D of modulation. When the noise is increased, only the TNN is able to close the loop, while the standard linear reconstructor fails even when a modulation is introduced. Using the GCViT, we closed a real AO loop in the optical bench and achieved a Strehl ratio between 0.28 and 0.77 for turbulence conditions corresponding to Fried parameters ranging from 6 to 20 cm, respectively. Conclusions. Through a variety of simulated and experimental results, we demonstrate that a TNN is the most suitable architecture for extending the dynamic range without sacrificing sensitivity for a nonmodulated PyWFS. It opens the path for using nonmodulated Pyramid WFSs in an unprecedented range of atmospheric and noise conditions

Specifying an MOAO-fed integral field spectrograph for the E-ELT

International audienceWe present an end-to-end simulator for 3D spectroscopy, which can be used to specify MOAO-fed integral field spectrographs dedicated to ELTs. This simulator re-scales either local data or outputs of hydro-dynamical simulations to model distant galaxies. We present simulations of 3D observations in the H-band, for a rotating disk and a major merger at z=4, and a large range of stellar-mass. We use these simulations to explore the parameter space, focusing on the impact of the telescope diameter, total integration time, spectral resolution, and IFU pixel scale. The size of the telescope diameter has little influence on the spatial resolution of 3D observations but largely influences the achieved SNR. The choice of the IFU pixel scale is driven by the optimal "scale-coupling", i.e., the relation between the spatial resolution of 3D observations and the physical size of the features for which one needs to recover the kinematics using this IFU, and the SNR achieved with this spatial scale. To recover the dynamical state of distant emission line galaxies, one of the main goal of such future instruments, one only needs to recover their large-scale motions, which in turn requires only relatively coarse IFU pixel scales (50-75 mas) and moderate spectral resolution (R=5000)

Focal-plane Cn2(h) profiling based on single-conjugate adaptive optics compensated images

International audienc

Fourier filter LGS wavefront sensing for ELT size telescopes

International audienc