  The expression for the total angular momentum carried by a laser optical
vortex beam, splits, in the paraxial approximation, into two terms which seem
to represent orbital and spin angular momentum respectively. There are,
however, two very different competing versions of the formula for the spin
angular momentum, one based on the use of the Poynting vector, as in classical
electrodynamics, the other related to the canonical expression for the angular
momentum which occurs in Quantum Electrodynamic. I analyze the possibility that
a sufficiently sensitive optical measurement could decide which of these
corresponds to the actual physical angular momentum carried by the beam.
