A future upgrade of the Keck II telescope’s adaptive optics system will include a near-infrared pyramid wavefront sensor. It will benefit from low-noise infrared detector technology, specifically the avalanche photodiode array SAPHIRA (Leonardo). The system will either operate with a natural guide star in a single conjugated adaptive optics system, or using a laser guide star (LGS), with the pyramid working as a low-order sensor. We present a study of the pyramid sensor’s performance via end-to-end simulations, including an analysis of calibration strategies. For LGS operation, we compare the pyramid to LIFT, a focal-plane sensor dedicated to low-order sensing.

HARMONI is a visible and near-infrared integral field spectrograph equipped with two complementary adaptive optics systems, fully integrated within the instrument. A Single Conjugate AO (SCAO) system offers high performance for a limited sky coverage and a Laser Tomographic AO (LTAO) system provides AO correction with a very high sky-coverage. While the deformable mirror performing real-time correction of the atmospheric disturbances is located within the telescope itself, the instrument contains a suite of state-of-the-art and innovative wavefront sensor systems. Laser guide star sensors (LGSS) are located at the entrance of the instrument and fed by a dichroic beam splitter, while the various natural guide star sensors for LTAO and SCAO are located close to the science focal plane. We present opto-mechanical architecture and design at PDR level for these wavefront sensor systems.

The Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) instrument is an extremely modular high- contrast instrument installed on the Subaru telescope in Hawaii. SCExAO has a dual purpose. Its position in the northern hemisphere on a 8-meter telescope makes it a prime instrument for the detection and characterization of exoplanets and stellar environments over a large portion of the sky. In addition, SCExAO’s unique design makes it the ideal instrument to test innovative technologies and algorithms quickly in a laboratory setup and subsequently deploy them on-sky. SCExAO benefits from a first stage of wavefront correction with the facility adaptive optics AO188, and splits the 600-2400 nm spectrum towards a variety of modules, in visible and near infrared, optimized for a large range of science cases. The integral field spectrograph CHARIS, with its J, H or K-band high-resolution mode or its broadband low-resolution mode, makes SCExAO a prime instrument for exoplanet detection and characterization. Here we report on the recent developments and scientific results of the SCExAO instrument. Recent upgrades were performed on a number of modules, like the visible polarimetric module VAMPIRES, the high-performance infrared coronagraphs, various wavefront control algorithms, as well as the real-time controller of AO188. The newest addition is the 20k-pixel Microwave Kinetic Inductance Detector (MKIDS) Exoplanet Camera (MEC) that will allow for previously unexplored science and technology developments. MEC, coupled with novel photon-counting speckle control, brings SCExAO closer to the final design of future high-contrast instruments optimized for Giant Segmented Mirror Telescopes (GSMTs).

The Gran Telescopio Canarias Adaptive Optics (GTCAO) will measure the wavefront with a Shack-Hartmann sensor. This wavefront sensor (WFS) is based on the CCD220, an electron-multiplying CCD (EMCCD) that achieves sub-electron readout noise, increasing the signal to noise ratio when weak natural guide stars (NGS) are used as reference. GTCAO will start its operation in telescope with NGS, using only one wavefront sensor, and later it will incorporate a Laser Guide Star (LGS) and consequently a second WFS, also based on an EMCCD. Both EMCCDs and a third one used as spare, have been characterized and compared including the system gain, electron- multiplication gain, readout noise vs gain, excess noise and linearity. The EM gain calibration is important to keep all EMCCD channels in the linear regime and the camera manufacturer carries it out, but it is reported that the multiplication gain may suffer ageing and degradation even if the camera is not in use. This suggests the need to monitor this ageing. In this paper it is proposed and tested a procedure for predictive maintenance that re-characterize the system gain, electron- multiplication gain and linearity periodically in order to predict the eventual ageing of the EMCCD multiplying registers. This procedure can be carried out quickly while the detector is installed in the WFS and in operational status. In order to provide the required illumination, the GTCAO calibration system is used.

The studies were carried out preliminary within the framework of the RSF project 15-19-20013 Creation of an adaptive system ensuring operation of a large-sized solar telescope under conditions of strong atmospheric turbulence. It is known that the use of adaptive optics (AO) systems is the most radical way for reducing the effect of atmospheric distortions. AO systems correct distortions introduced by the Earth's atmosphere into the image of a space object in real time. The creation of an AO system for large-aperture solar telescopes still is a scientific and engineering challenge. Currently, for the largest Russian solar telescopes, in particular, the Large Solar Vacuum Telescope (LSVT), the Automated Solar Telescope (AST) and the 3-meter Large Solar Telescope (LST) under development, promising new- generation systems are being developed and implemented based on the principles of multi-mirror adaptive correction.

The optical turbulence characteristics statistics including seeing, Fried radius, wind speed height profiles are discussed. Distribution of the mean Fried radius obtained from the data of image motion measurements by the Brandt sensor is given. Also, the Fried radius values calculated from the Shack-Hartmann data are given. Using the height profile of the structure characteristic of air refractive index fluctuations obtained from spectral multiscale turbulence model the results of the Fried radius simulations from micrometeorological mast measurement data given.

MAORY is the Multi-Conjugate Adaptive Optics module for the European ELT. It will provide a wide-field correction for the first-light instrument MICADO. The Low-Order wavefront modes will be sensed on 3 Natural Guide Stars with Shack-Hartmann Wavefront Sensors, so-called the LO WFS. In the presented work, we focus on the numerical study of the main aspects that depend on the LO WFS design and operational use: low-order sensing performance and sky coverage.

International audience

The Sun is an ideal object for the development of Multi-Conjugate Adaptive Optics (MCAO) since solar structure provides multiple “guide stars” in any desired configuration. Current MCAO systems imply a number of wavefront sensors, each of them sensing an area of the Sun. The plenoptic camera is a novel concept for wavefront sensing, capable of measuring the tomography of the atmospheric turbulence. By using it, the possibility of a MCAO system with a single sensor becomes a reality. This paper describes the functionality of the plenoptic camera as a tomographic wavefront sensor after implementing it into the OOMAO simulator. Simulation results demonstrate the potential of this sensor to reconstruct atmospheric turbulence in different layers by using a synthetic solar image as a reference.

The European Solar Telescope (EST) will provide spectro-polarimetric measurements of the solar atmosphere with unprecedented sensitivity and accuracy. To this purpose, its optical scheme, as well as its MCAO system, are designed to minimize the instrumental polarization. In the framework of the EST design, we have started a series of laboratory tests to characterize the effects of using deformable mirrors on polarization measurements. In this contribution, we will show the results of these tests. These results are not only relevant to solar physics, but also to a number of other astrophysical research fields where high precision polarimetry is becoming a fundamental tool, such as for example exoplanets detection, and star formation characterization.