Degeneracy in the diffraction of orbital angular momentum carrying beams.

Symmetry constraints on the far-field diffraction of Laguerre-Gauss vortex beams by planar aperture arrays with N-fold rotational symmetry are considered. The experiments reveal a simple structure for the diffraction pattern and high degree of degeneracy in its dependence on the orbital angular momentum index of the incident beam in agreement with analytical and numerical results. (C) 2018 Optical Society of America