Phase structure of helico-conical optical beams

We examine the phase structures of Helico-Conical (HC) Optical Beams produced via computer-generated holograms (CGH). The CGHs of these beams are made such that the reconstruction will have a phase which is a product of a helical and a conical phase. Interference-based phase measurement technique reveals very distinct differences between the phases of the two types of HC Beams (K = 0 and K = 1). Most obvious is the presence of screw dislocations at the center of the beam for K = 1 while no screw dislocations are found at the center for K = 0. We also compare the experimental interference patterns with numerical interference patterns calculated by superimposing a field containing vortices at different positions and a plane wave. A remarkable similarity is seen between the interferograms, which is a good indication of the phase of these beams. Contour plots are drawn to show the phases of these beams. We observe a string of vortices with equal charge in contrast to the assumption that a string of alternating charges should be seen.