OAM beam diffraction by a triangular aperture and a triangular slit: a comparative study
The far-field diffraction patterns (FDPs) of an optical vortex beam by a triangular aperture and a triangular slit are analyzed and compared. We find that for both, the patterns exhibit a truncated optical lattice array which is related to the topological charge of the beam. Compared to the aperture where both geometric and boundary waves contribute to the formation of lattices, the slit produces dimmer FDPs because of the presence of the boundary waves only. However, the average contrast of the patterns by the slit defined as the ratio between the spread and the sum of the minimum and maximum intensities is 40% higher than those by the aperture. This means that it is easier to decide the maxima points contained in the FDPs when using the slit compared to the aperture that is necessary for determining the orbital angular momentum of light.