Multi-Conjugate Adaptive Optics for LINC-NIRVANA : Laboratory Tests of a Ground-Layer Adaptive Optics System and Virtical Turbulence Measurements at Mt. Graham

Turbulence in Earth's atmosphere severely limits the image quality of ground-based telescopes. With the technique of Adaptive Optics, the induced distortions of the light can be measured and corrected in real-time, regaining nearly diffraction-limited performance. Unfortunately, when using a single guide star to measure the distortions, the correction is only useful within a small angular area centered on the guide star. The first part of this thesis presents a laboratory setup, which uses four guide stars to measure the turbulence-induced distortions and one deformable mirror to correct the most turbulent layer. With such a Layer-Oriented Ground-Layer Adaptive Optics (GLAO) system, the area of useful correction is significantly increased. The system is characterized in static and dynamic operation, and the influence of non-conjugated turbulent layers, the effect of brightness variations of the guide-stars and the impact of misalignments are studied. Furthermore, calibration strategies and the performance of the Kalman control algorithm are examined. The second part of this thesis focuses on SCIDAR measurements of the atmospheric turbulence above Mt. Graham. This dataset provides for the first time a statistical and thorough analysis of the vertical turbulence structure above the LBT site. Based on 16 nights of measurements, spread over one year, Mt. Graham appears to be an excellent site for an astronomical observatory. By extending an analytical model, describing the filtering of the turbulence-induced distortions by an AO system, we calculate performance expectations of the LINC-NIRVANA instrument. In particular, the optimal conjugation heights of the deformable mirrors are studied. Furthermore, we present a new method to measure the atmospheric turbulence near the ground with 40 times increased vertical resolution, compared to standard SCIDAR. First on-sky results demonstrate the power of this technique