6.2 Measured performance of AO

Figures of merit for AO system performance include the achieved Strehl ratio and the residual wavefront error. However, it is most desirable to have knowledge of the AO corrected PSF because the most detailed AO performance analysis and optimization of the system can be performed. Furthermore, if the PSF is known, image reconstruction techniques can be deployed to further improve the AO corrected images. Solar AO is at a distinct disadvantage here because estimation of the PSF is not straightforward. For night-time AO the observed object is often a point source or a point source can be found nearby. The PSF can be estimated directly from the corrected image of the point source (Roberts Jr et al., 2004). For solar images one could deploy post-facto PSF estimation techniques such as phase diversity. However, for estimating the long exposure PSF provided by the AO system as a function of r0 it is convenient and efficient to use the information the AO system itself can provide. Some post-facto reconstruction techniques, such as speckle interferometry (Wöger et al., 2008Jump To The Next Citation Point) that work with short exposure imaging also require this AO telemetry information.
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