Beaming effect of the plasmonic metalens structured with concentric elliptical nanohole arrays

The beaming effect of plasmonic metalens, comprising two concentric elliptical nanohole arrays in a silver film, was explored using experimental methods and numerical simulations. Owing to the birefringent effect of the elliptical nanohole, the rotation of the elliptical major axis and the thickness of the silver film influence the polarization state and magnitude of the light transmitted from the elliptical nanohole. The polarization state of the metalens affected the corresponding diffraction pattern. The birefringent effect of the metallic elliptical nanoholes is related to the ohmic loss of the metal. The ohmic loss influences the beaming effect of plasmonic metals. In this study, we use linearly polarized light in the near-ultraviolet and visible regimes to evaluate the beaming effect through the influence of ohmic loss. Two orthogonal polarizations were generated on the metalens, wherein the major axis of the elliptical nanohole in the inner concentric array was perpendicular to the major axis of the elliptical nanohole in the outer concentric array. The metalens generate transmitted light with a strong focusing ability by generating two orthogonal polarizations. An optical beam with a small focusing spot and long working distance can be obtained from these plasmonic metalens.