Adaptive optics system for a 1.5-m solar telescope

We describe an adaptive optics system for the 1.5m diameter solar telescope GREGOR which is currently developed for the Teide Observatory on Tenerife. In a first development step, the AO will provide compensation of 77 modes of wavefront deformation, corresponding to the first 10 radial degrees of a Karhunen-Loeve decomposition of wavefront error. We estimate that such a performance will render GREGOR nearly diffraction limited at visible wavelengths in conditions which correspond to the best 25% of the seeing In Tenerife. The AO uses a Shack-Hartmann wavefront sensor which operates on fine structure anywhere on the solar disk. The required control bandwidth will be about 200 Hz. We show how such a system can be realized using existing technology. Substantial increases in performance in terms of corrected wavefront error and field requires significant technological advances, in particular in the field of large field high speed detectors.