Experimental Adaptive Optics. A test facility for adaptive optics on a small telescope

Sammanfattning: This thesis presents the work on the design of, construction of, and finally observations with, an experimental setup comprising a small telescope equipped with adaptive optics. The facility has been assembled at Lund Observatory, where also observations on the sky have been made. The aim of this project was to gain hands-on knowledge in the development of a real adaptive optics system and eventually also to use the setup for evaluation of novel adaptive optics techniques, i.e. multi-conjugate adaptive optics (MCAO) and ground-layer adaptive optics (GLAO), within the field of astronomical adaptive optics. In order to enable the facility to test these novel techniques, multiple reference sources are needed for the adaptive optics system. Due to the poor observing site, a multiple guide star configuration is not expected to exist. Instead, surface features on the Moon were foreseen to act as reference sources. Hence the radiometric properties of the Moon have been studied, to evaluate the expected signal. Use of extended reference sources demands correlation analysis in connection with the Shack-Hartmann wavefront sensing, and this procedure has also been studied during the work. The method relies on the phase of the cross correlation spectrum, and this method has been used in the succeeding implementation of the control system. The optical design of the facility has taken into account allowance of multi-conjugate adaptive optics and ground-layer adaptive optics. Two deformable mirrors are used, one in a conjugate plane to an altitude in the atmosphere and one in a pupil-conjugate plane. Furthermore there is a tip-tilt mirror in a pupil-conjugate plane. A single Shack-Hartmann sensor, with separated subregions in the lenslet focal plane to allow multiple reference regions, is used for the wavefront sensing. The system is operating at an effective wavelength of 750 nm. A standard desktop PC, running Linux, has been used as a control computer in the control system. The maximum sampling rate is 500 Hz, correcting turbulence induced aberrations up to approximately 30 Hz. The setup was assembled in the lab before it was moved up into a dome for observations on the sky. Much effort has been put into reducing static aberrations, which have limited the performance. Evaluation of the setup has been achieved both in the lab and during observations on the sky. Using a simplified model atmosphere, more benign than the real atmosphere, the gain in using MCAO and GLAO compared to conventional single-conjugate adaptive optics (SCAO) could be demonstrated in the lab. During on sky observations, it has so far been possible to close the SCAO loop on bright stars and on the lunar surface as well with significant increase in image quality.