Mode Purity Analysis for the Vortex Beam Emitter

Vortex beams have exhibited great potential in multiple areas such as optical tweezers, quantum entanglement, and nonlinear optics. Various approaches have been developed for generating vortex beams such as spiral phase plates. Recently, a novel approach based on chiral plasmons has been proposed, which generates vortex beams with multiple topological charges (TC) in broad tunable bands. In this study, we investigate the mode purity of the vortex beams emitted by this approach. Using the Finite-Difference Time-Domain method, we calculate the purity of various modes in a broad frequency band. It verifies the approach can generate high-purity vortex beams with various TCs in the broadband. This study about the mode purity analysis contributes to further applications of vortex beams generated using the approach based on chiral plasmons.