Plasmonic metasurface Luneburg lens

We present a new design of a plasmonic Luneburg lens made from a gradient-index metasurface that wasconstructed with an array of nanometer-sized holes in a dielectric thin film. The fabricated structure consistsof a planar lens with a diameter of 8.7μm composed of a rectangular array of holes with a periodicity of300 nm. The experimental characterization includes leakage-radiation microscopy imaging in the directionand frequency space. The former allows for characterization of the point spread function and phase distribution,whereas the latter grants access to qualitative measurements of the effective mode indices inside the plasmoniclens. The experimental results presented here are in good agreement with the expected average performance pre-dicted by the numerical calculations. Nevertheless, the robustness of the characterization techniques presentedhere is also exploited to determine deviations from the design parameters.