Direct Determination of Laguerre-Gauss Vortex Beams' Topological Charges by Aperture Diffraction Pattern

The vortex beam with the positive and negative topological charge was prepared by the dislocation fork grating. Then the diffraction experiments of circular aperture, triangle aperture and square aperture were carried out. The results show that the diffraction pattern of the vortex beam passing through the circular aperture cannot distinguish the positive and negative of topological charge, and the topological charge of the vortex beam can be determined by the direction of the distortion of the diffraction spot of the circular aperture, triangular aperture and square aperture. This conclusion provides a simple method for the detection of Orbital Angular Momentum (OAM).