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ARGOS is the laser guide star ground layer adaptive optics system of the LBT.ARGOS is designed to bring a moderate but uniform reduction of the PSF sizeover a FoV as large as 4x4arcmin, allowing a significative increase of thescience throughput of LUCI, the LBT NIR imager and MOS. ARGOS relays on 3Rayleigh beacons to sense the lower layers of the atmosphere achieving almost100% sky coverage. The ground layer AO correction is allowed by the 2 adaptivesecondaries of the LBT. This PhD thesis first discusses a study based onnumerical simulations and aimed to evaluate the performance of ARGOS. This workhas been carried out using CAOS and representing in the code most of thefeatures that characterize the system itself: as the laser beacon propagationin the atmosphere, the SH type wavefront sensing, the AO reconstruction andclosed loop delays and the atmosphere tip-tilt sensing done using a NGS and aquad-cell type sensor. The results obtained in this study are in agreement anddefinitively confirm the performance evaluated in the phase studies of theproject. This study shows that ARGOS is able to produce a reduction of a factor2 of the seeing bringing to a gain of a factor 4 in the integration timerequired by LUCI. This PhD thesis reports also the optical design andoptimization of both the ARGOS dichroic window, used to separate the laserlight from the science light, and the LGS WFS, that evaluates the ground layeraberrations averaging the SH measurements in the direction of the 3 LGS. Forboth of the subsystems the optimization process is analyzed. Then are evaluatedthe tolerances and specifications for the production and coating of the optics.Finally are evaluated the stability requirement for the mechanical design andthe degrees of freedom needed for the alignment purposes.

Design of the wavefront sensor unit of ARGOS, the LBT laser guide star system