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Measurement of laser spot quality

Several ways of measuring spot quality are compared. Examination in detail is made of various figures of merit such as full-width-at-half maximum (FWHM), full-width-at-1/e2 maximum, Strehl ratio, and encircled energy. The paper describes application for optical data storage, but results can be applied to other areas like space communications and high-energy lasers. The finding is that the optimum figure of merit in many cases is Strehl ratio.