Abstract

Spin and orbital angular momentum densities are connected to helicity (circular polarization) and topological charge (azimuthal phase shift and vorticity). Computing the electromagnetic fields emitted by a circular antenna array, analytic expressions are found for the densities of energy, linear momentum, and angular momentum in terms of helicity and vorticity. Separating the angular momentum into spin and orbital angular momentum, we find that the density of orbital angular momentum depends on the vorticity only and can be expressed by quite simple terms, whereas the density of spin angular momentum depends on both, helicity and vorticity. Finally, a radio experiment is proposed that allows to measure the torque of the angular momentum flux.

The presentation (PDF)