Correction of non-common-path error for extreme adaptive optics

The future direct imaging of exoplanets depends critically on wave-front corrections. Extreme adaptive optics is being proposed to meet such a critical requirement. One limitation to the performance of adaptive optics is the differential wave-front aberration that is not measured by a conventional wave-front sensor because of the so-called non-common-path error. In this article, we propose a simple approach that can be used to eliminate differential aberration with extreme adaptive optics and is optimized for best image performance or directly optimized for high-contrast coronagraphic imaging. The approach that we propose can correct differential aberration in a single step, which guarantees high accuracy and allows adaptive optics to correct the differential aberration on a real-time scale. This approach is based on an iterative optimization algorithm that commands the deformable mirror directly and uses the focal-plane point-spread function as a metric function to evaluate the correction performance.