?± spiral nanoslit and the higher order plasmonic vortex generation

摘要： In view of the conciseness of a spiral nanoslit and the limited order of the generated vortex, a kind of nanometer spirals named α spirals are proposed to generate the higher order plasmonic vortex. Theoretical analysis provides the basis for the advancement of α spiral. The proposed spiral can generate the plasmonic vortex and the extreme order of the generated vortex depends on the parameter α. The numerical simulations definite the valid region of the plasmonic vortex generated by the α spiral. Discussions about the validity range of the α spiral nanoslit and the influence of the film material are beneficial to generate the high order vortex. This work builds a platform for the generation of the higher order plasmonic vortex using the simple spiral nanostructure and it can extend the potential applications of higher order plasmonic vortices.