Propagation and diffraction of optical vortices (2008) by Pascal Fischer, Susan E. Skelton, Christopher G. Leburn, Casey T. Streuber, Ewan M. Wright, Kishan Dholakia
Generation of Optical Vortices by Converting Elegant Hermite Gaussian Beams (2005) by Megumi Okamoto and Hiroyuki Sasada
Phase singularities in beams (1999) by G. F. Brand