Perfect (optical) vortices (PVs) have attracted significant interest in the optical community owing to their well-defined annular ring whose near-field radial profile is independent of orbital angular momentum (OAM). Although it is a general belief that it is not possible to perform quantitative OAM measurement of PVs by modal decomposition, here we show, both theoretically and experimentally, that the OAM content of a PV can be measured quantitatively in both the near- and far-fields, including superpositions of OAM within one perfect vortex. Our work will be of interest to the large community who seek to use such structured light fields in various applications, including optical trapping and tweezing and optical communications.
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