Abstract

There are different techniques for sensing wavefront phase distortions due to atmospheric turbulence. Curvature sensors are practical because their sensitivity is adjustable to the prevailing atmospheric conditions. Even at the best sites, the turbulence intensity has been found to vary at times over only a few minutes and regularly over longer periods. Two methods to automatically adjust the sensitivity of a curvature sensor are proposed: First, the defocus distance can be adjusted prior to the adaptive-optics (AO) loop through the acquisition of a long-exposure image and can then be kept constant. Second, the defocus distance can be changed during the AO loop, based on the voltage values sent to the deformable mirror. We demonstrate that the performance increase—assessed in terms of the image Strehl ratio—can be significant.

© 2010 Optical Society of America

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