Singularities of optical currents, competition of local orbital angular momenta in astigmatic Gaussian beams, and...

As a rule, transitions between the optical current singularities in vortex beams with a general astigmatism are associated with changes in featured orbital angular momentum (OAM) states (zeros and extremes). However, we have brought to light significant differences in transforming optical current singularities and the OAM in vortex and vortex-free astigmatic Gaussian beams. First of all, this is manifested in the sequential conversion of optical current singularities in a Gaussian beam with a simple astigmatism, whose OAM is always zero. Besides, in the case of general astigmatism, the conversion of optical current singularities does not coincide with the OAM transformations, but has a wide range of propagation of the astigmatic Gaussian beam. Such a mismatching indicates the competing processes in optical currents during the beam propagation. We evaluated the competing processes based on the mechanical model of optical currents and the OAM. We found that a combined contribution of the local OAMs leads to the effect of matching the total OAM with a physically measurable cross-intensity moment. This effect enabled us to develop and implement a technique for measuring small and large OAM in astigmatic Gaussian beams.