Measuring the orbital angular momentum of elliptical vortex beams by using a slit hexagon aperture

The far-field diffraction pattern of an elliptical vortex beam by a slit hexagon aperture is investigated theoretically and experimentally. It is found that the number of the dark spots or stripes in the Fraunhofer diffraction intensity distribution is just equal to the topological charge value of the measured optical vortex, and that the centre of each dark spot or stripe is just a phase singularity point. Based on this property, it provides us a simple way to detect the orbital angular momentum (OAM) of an optical vortex beam.

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► The number of the dark stripes is equal to the OAM of the measured optical vortex.
► The centre of each dark stripe is a phase singularity point.
► The experimental results are consistent with the theoretical ones.
► It provides us a simple way to detect the OAM of an elliptical vortex beam.