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Design of ground-layer turbulence compensation with a Rayleigh beacon

The adaptive optics instrument for the SOAR 4.1-m telescope will improve the spatial resolution by 2-3 times at visible wavelengths, over a field of 3 arcmin, by sensing and correcting low-altitude turbulence selectively. We will use a Rayleigh laser guide star to accomplish this. We present the laser guide star design with predictions of system performance based on real turbulence statistics and telescope properties, sky coverage and some opto-mechanical aspects of the AO module. Various design trade-offs are discussed.