Spatial coherence singularities of a vortex field in nonlinear media
  We study the spatial coherence properties of optical vortices generated by partially incoherent light in self-focusing nonlinear media. We reveal the existence of phase singularities in the spatial coherence function of a vortex field that can characterize the stable propagation of vortices through nonlinear media. 
Kristian Motzek, Yuri S. Kivshar, and Grover A. Swartzlander Jr