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Momentum paradox in a vortex core

Zambrini, R and Thomson, L C and Barnett, S M and Padgett, M (2005) Momentum paradox in a vortex core. Journal of Modern Optics, 52 (8). pp. 1135-1144. ISSN 0950-0340

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The identification of angular momentum l (h) over bar per photon with optical vortices of charge l appears to require that the field amplitude be zero within a finite distance of the vortex. This, however, is not compatible with the known form of beams such as the Laguerre - Gaussian and Bessel beams. We resolve this paradox by analysing the propagation of a Bessel beam through a small circular aperture, showing that the resulting field has evanescent components.