Pancharatnam-phase-based characterization for the diffraction of an optical vortex beam

We present an interferometric method to recover the phase diffraction patterns of a Gaussian optical vortex (OV) beam with different topological charges. The patterns are encoded and converted into polarization information, which can be decoded and measured by an analyser and a camera. Helical diffraction structures due to the spiral phase plates are obtained by a Mach-Zehnder interferometer. A numerical method based on angular spectrum representation is developed to simulate both the polarization and the distorted phase pattern of the OV beam through propagation. Simulation results show good agreement with the experiment.