Spin attributes of structured vector fields constructed by Hertz potentials

In this paper, we use the Hertz vector potential to define the electromagnetic vector of different structured wavefields, and analyze the spin properties of the wavefields. We show that for the single evanescent waves, the total spin provides by the transverse spin and originates from the spatial inhomogeneity of the momentum density of the field. However, for non-single evanescent wave, there may be a part of the extraordinary spin component sE, and the direction of sE is also perpendicular to the wave propagation direction. In other words, it is transverse, but it does not originate from the curl of the wave field momentum density. In addition, we also calculate the spins of non-planar propagating waves, and analyze the spin characteristics of these wave fields.