Momentum paradox in a vortex core

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.