Circularly coherent vortex beams with coherence singularities in free-space propagation

Circularly coherent sources, which are perfectly coherent on any ring that is concentric to the beam center, can preserve the spiral phase structures of optical vortices on propagation, making them potentially useful for free-space applications such as communications and remote sensing. In this study, we theoretically examine circularly coherent vortex beams by imposing circular coherence on Laguerre-Gaussian (LG) beams. The second-order coherence properties and coherence singularities of these circularly coherent vortex beams are investigated in free-space propagation up to 3 km. We discuss the noteworthy features of such beams, including self-focusing that arises due to the circular coherence.