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Non Common Path Aberrations (NCPA) are a usual problem encountered when using an Adaptive Optics System (AO)to produce corrected images in an astronomical instrument. The usual way to correct for such NCPA is to introduce anoffset in the WaveFront Sensor (WFS) signals that corresponds to the aberration to correct. In such a way, when the AOloop is closed, the Deformable Mirror (DM) will converge to the shape required to null the NCPA. The method assumesthat the WFS operation is linear and completely described by some pre-calibrated interaction matrix. This is not the casefor some frequently used wavefront sensors like the Pyramid sensor or a quad-cell Shack-Hartmann sensor. Here wepresent a method to work in closed loop with a Pyramid Wavefront Sensor (PWS), or more generally a non linear WFS,while introducing a static offset on the DM. The DM shape is kept constant even if the AO residuals change over timebecause of variations of seeing, wind speed and so on. Results from numerical simulation and first on sky data from LBTFLAO system and LUCI2 facility instrument are presented.

A new coronagraphic instrument for the Large Binocular Telescope (LBT) has successfully passed the conceptual design phase. SHARK-NIR channel will be installed in one arm of the Large Binocular Telescope and it is designed to use different coronagraphic techniques, both to match as much as possible the different requirements of the different science cases and to explore the capabilities of such techniques for the next-generation of ELTs. By exploiting the combination with SHARK-VIS channel mounted at the other LBT arm, the instrument will offer simultaneous coronagraphic observations at different wavelengths, characterized by high contrast, even for relatively faint targets. This will be achievable thanks to the very efficient Adaptive Optics (AO) systems already operating at LBT (First Light AO, FLAO). Furthermore, the latter will be soon upgraded with new detectors, promising even better performance in terms of limiting magnitude. In this paper we present the status of the SHARK-NIR channel design.

During the past decade, there has been a remarkable expansion of the application of wavefront-related technologies to the human eye. The ability to measure the wavefront aberrations (WA) of an individual eye has greatly improved our understanding on the optical properties of the human eye. The development of wavefront sensors has further generated an intensive effort to revise methods to correct vision. Wavefront sensors have offered the promise of a new generation of visual correction methods that can correct high order aberrations beyond defocus and astigmatism, that is, the wavefront-guided excimer laser platforms and adaptive optics, thus improving visual performance or fundus imaging at unprecedented spatial resolution. On the other hand, current wavefront technologies suffer from some inaccuracies that may limit a wider expansion in the clinical environment. Several innovative approaches have been developed to overcome the limits of standard wavefront sensing techniques. Curvature sensing, pyramid sensing and interferometry currently represent the most reliable methods to revise and improve the measurement and reconstruction of the WA of human eyes. This review describes advantages and disadvantages of current wavefront sensing technologies and provides recent knowledge on innovative methods for sensing the WA of human eyes. In the near future, we expect to benefit from these new wavefront sensor elements, including their application in the personalised correction of optical aberrations and adaptive optics imaging of the eye. [ABSTRACT FROM AUTHOR]

A three-sided pyramid prism is used as a wavefront sensor in non-modulating mode with an artificial neural network (NN) as a control unit in an adaptive optical setup. The NN is composed of a convolution network for feature extraction from the pyramid signal and a three-layer feed-forward back-propagation net. The network is trained with over 15,000 examples of signal-wavefront pairs. Presenting wavefronts of 6 mm pupil diameter and a RMS error of under 200 nm to the adaptive optical system with the trained network, it can correct the aberrations within three loops to a wavefront with <60 nm root mean square (RMS) error. [ABSTRACT FROM AUTHOR]