Plasmonic lenses with long focal lengths

We report on recent progress made in the development of plasmonic nanolenses. These lenses exhibit intensity transmittance close to 80%, focal lengths equal to one or more wavelengths, and foci with full-widths at half-maximum close to the diffraction limit. We consider lenses in the form of (i) a silver layer with no hole on the optical axis and double-sided concentric corrugations, (ii) a silver layer with no hole on the axis and single-sided corrugations, and (iii) a lens composed of several concentric metallic rings and on-axis stop with external layer of transparent dielectric that integrates all elements. Investigations are carried out using the Finite-Difference Time-Domain method and the Transfer Matrix Method. The nanolenses are diffractive optical elements that concentrate radially polarized Laguerre-Gauss illumination as tightly as high-NA refractive optical systems.