Single-layer metal nanolenses with tight foci in far-field

Abstract

In simulations we analyze performance of plasmonic nanolenses made of a single metal layer. We consider the nanolenses in two configurations. In the first, the nanolens is a free-standing silver layer with no hole on the optical axis and double-sided concentric corrugations. In the second, the nanolens has a set of slits instead of grooves. This necessitates integrating the annular metal elements with a dielectric matrix. We examine the following parameters of the nanolenses: film thickness, diameter of an on-axis stop, and lattice constant of slits or double-sided concentric grooves, as well as depth and width of grooves. Due to radially polarized illumination lenses have foci of full widths at half maxima (FWHMs) better than half a wavelength, though foci formed by propagating waves do not decrease beyond the diffraction limit. Due to proper geometry of slits or double-sided grooves lenses have focal lengths of the order of a few wavelengths. Transmission of light through lenses with double-sided narrow grooves reaches 30% while through ones with slits exceeds 80%.

Plasmonic lenses with long focal lengths

“…The second lens considered here is a free-standing continuous silver layer with no hole on the optical axis and concentric corrugations on one side of the lens. In the third one grooves are replaced with slits [4,5]. A lens of this form is composed of several concentric metallic rings and on-axis stop which need an additional, external layer of continuous material to integrate all elements.…”