In the last 50 years the apertures of the world largest ground-based telescopes doubled, passing from the 5 m of the Hale telescope (1948) to the over 10 m of the Gran Telescopio Canarias, serving the astronomers in their attempts to push further and further the boundaries of our knowledge of the sky. The astronomical community is now looking forward to the era of the 40 m telescope (Extremely Large Telescope, ELT), which will further improve the studies in many astronomical fields, enabling the observation of very faint and distant objects, beyond the limits of the currently known universe.
However, since these telescopes are located on the ground and they are naturally affected by atmospherical seeing, even the largest telescope would be equivalent, in term of resolution and image quality, to a telescope of few tens of centimetres in diameter, if the seeing is not compensated.
This is exactly the aim of Adaptive Optics, which plays a key role in the modern ground-based telescope, as it allows the telescope to recover, completely or partially, its theoretical resolution imposed by diffraction. Many different kinds and approaches to Adaptive Optics have been proposed in the last decades, each one with its level of correction, sky coverage, complexities etc.
LINC-NIRVANA, the Fizeau interferometer for the LBT, is equipped with a complex Multi-Conjugate Adapive Optics system (MCAO), which allows to uniformily correct a 2 arcmin Field of View, enabling interferometric imaging on a 10 x 10 arcsec Field of View with a 23 m telescope equivalent resolution. When operated in this configuration, the LBT can be considered a precursor of the ELTs.
In this Thesis I give a detailed description of the MCAO system serving LINC-NIRVANA, and in particular of its main subsystems, the Ground layer Wavefront Sensor (GWS) and the High layer Wavefront Sensor (HWS). I give an overview of the optical concepts and layout of the MCAO module, going through the definition of the alignment procedures defined to match the tight tolerances required to correctly operate the instrument, and concluding with the results and verifications of the alignment.
I also widely describe the operations and the results of a Pathfinder Experiment, in which one of the two GWSs has been tested at the LBT as a stand alone system in order to verify its ability to drive the Adaptive Secondary Mirror of the LBT and also our ability to make it possible. In this way we acquired experience in view of the LINC-NIRVANA commissioning, planned at the end of 2016.
Since LINC-NIRVANA is an Italian/German collaboration, the work described in this Thesis was carried out in three countries: Italy, Germany and U.S.