Plasmonic interaction of light with negative index and gold nano-checkerboards

TL;DR

This paper explores the theoretical and numerical properties of negative index materials and gold nano-checkerboards, demonstrating their unique plasmonic interactions and potential for sub-wavelength imaging and enhanced electromagnetic fields.

Contribution

It introduces a generalized lens theorem for structured NRIM slabs, maps checkerboards onto corner lenses via transformational optics, and experimentally investigates gold checkerboards with enhanced plasmonic responses.

Findings

Checkerboard NRIM slabs support strongly enhanced electromagnetic fields.

Gold nano-checkerboards exhibit unique scattering spectra due to plasmonic interactions.

Transformational optics maps complex structures onto corner lenses, enabling novel designs.

Abstract

Negative refractive index materials (NRIM) make possible unique effects such as a convergent at lens due to the reversed Snell-Descartes laws of refraction. NRIM are also known to be able to support a host of surface plasmon states for both polarizations of light which are responsible for the sub-wavelength image resolution achieved by a slab of NRIM. A generalized lens theorem provides us with a class of spatially varying slab lenses satisfying the prerequisite symmetries to fold the optical space onto itself. This theorem can be derived using powerful tools of transformational optics. A paradigm of such complementary media are checkerboards consisting of alternating cells of positive and negative refractive index that represent a very singular situation in which the local density of modes at the corners are enormously enhanced. We have considered several theoretical and numerical aspects of such structured films including a finite slabs of multi-scale checkerboards of NRIM satisfying the generalized lens theorem which are host of strongly enhanced electromagnetic feld. Such checkerboards can be mapped using transformational optics onto three-dimensional corner lenses consisting of semi-infinite heterogeneous anisotropic regions of space satisfying the generalized lens theorem. It is also possible to design three-dimensional checkerboards of complementary media, the only restriction being that corresponding unfolded structures in the plane are constrained by the four color theorem. Some of these meta-surfaces in the plane display thin bridges of complementary media, and this further enhances their plasmonic response. Since plasmonic metals mimic the behaviour of NRIM at small length scales, opaque gold films structured at sub-micron scales in a checkerboard fashion were fabricated using focussed-ion-beam technologies and their scattering spectra measured.