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It is well known that Adaptive Optics (AO) observations do require the availability of natural stars (beside laser guide stars - LGSs) to obtain the tip-tilt and focus information of the atmospheric turbulence. Bright natural stars are not always available imposing the ultimate limit to the AO technology due to the small technical field planned for 40m range telescopes. The use of multiple LGSs, with their respective wavefront sensors and tomographic computations, requires the proper reconstruction of the turbulence column adding significant complexity and cost to the Adaptive Optics systems. Precise knowledge of the tip-tilt information is extremely useful for the accurate pointing of lasers in groundto-space optical communications and in space situational awareness applications. In these contexts the tip-tilt information cannot be obtained from natural stars. Our group have proposed an alternative way of measuring all relevant values of the atmospheric turbulence, specifically including tip-tilt, focus and also higher order aberrations, and tomographic information based on the use of the foreseen density anisotropies in the sodium layer. Results of an analysis using the available information about sodium layer profiles will be presented, showing up to what point anisotropies with the proper spatial and time scales could be expected. The requirements of a laser launch system capable of illuminating uniformly the metapupil at the height of the Na layer are identified and special attention is paid to the required laser power. The extended object generated at the Na-Layer should then be analysed with a wavefront sensor suited to that characteristic. The plenoptic camera is the potential candidate under study in this paper.

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 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 Uplink Wavefront Corrector System (UWCS) has been conceived by following the premises from simulation outcomes as a pathfinder instrument to demonstrate Adaptive Optics uplink correction in both applications: Free-Space Optical Communications and self-propagating path of Laser Guide Stars. Preliminary design and expected performance have been analysed via simulations in previous studies. Current activities focus on the turbulence measurement on the launch axis itself by using pulsed or modulated lasers and a pulse-synchronized Shack-Hartmann as wavefront sensor. Present paper describes the test bench it has been built in the Instituto de Astrofisica de Canarias (IAC) to experimentally demonstrate the uplink correction and its advantages.

Adaptive optics are techniques used for processing the spatial resolution of astronomical images taken from large ground-based telescopes. In this work are presented computational results from a modified curvature sensor, the Tomographic Pupil Image Wave-front Sensor (TPI-WFS), which measures the turbulence of the atmosphere, expressed in terms of an expansion over Zernike polynomials.

The Optical Ground Station (OGS), installed in the Teide Observatory since 1995, was built as part of ESA efforts in the research field of satellite optical communications to test laser telecommunication terminals on board of satellites in Low Earth Orbit and Geostationary Orbit. As far as one side of the link is settled on the Earth, the laser beam (either on the uplink or on the downlink) has to bear with the atmospheric turbulence. Within the framework of designing an Adaptive Optics system to improve the performance of the Free-Space Optical Communications at the OGS, turbulence conditions regarding uplink and downlink have been simulated within the OOMAO (Object-Oriented Matlab Adaptive Optics) Toolbox as well as the possible utilization of a Laser Guide Star to measure the wavefront in this context. Simulations have been carried out by reducing available atmospheric profiles regarding both night-time and day-time measurements and by having into account possible seasonal changes. An AO proposal to reduce atmospheric aberrations and, therefore, ameliorate FSO links performance is presented and analysed in this paper

During the last 20 years, many DIMM instruments have been developed to measure astronomical seeing. The IAC has been involved in several projects to run different campaigns to characterize its observatories. However, the cost in manpower to maintain and operate these instruments has been too high and it is mandatory to minimize this effort by constructing a reliable, robust and available seeing monitor. A review of all sources of errors has been done in order to fit very reliable measurements: acquisition parameters, box size, signal threshold, SNR threshold, flux, deformations and vibrations for centroid calculations, best pixel scale, jitter in the images sampling, light bandwidth, CCD noise, as well as the centroid calculation algorithm. Experimental measurements about the influence of exposure time, number of images for computing the seeing or defocus have been carried out to identify the practical limits of the instrument. The IAC automatic DIMM design has been reviewed to improve its robustness and its availability to guarantee the minimum down-time and to maximize the time between failures. The new design will be shown as part of this work.