Remote grating-assisted excitation of narrow-band surface plasmons

Tae-Woo Lee,Stephen K Gray

doi:10.1364/oe.18.023857

Abstract

We show, based on theoretical analysis and realistic simulations, how a grating embedded in a dielectric substrate can excite surface plasmon polaritons (SPPs) on the top side of a flat metal film far removed from the grating. This remote SPP excitation is characterized by a narrow spectral bandwidth and a high near-field intensity relative to the standard approach for exciting SPPs. The simplicity of the structure and the fact that it requires only normally incident light should make it relevant to the many applications that benefit from high quality SPPs on a flat metal film.

Highlights

Surface plasmons (SPs) are electromagnetic excitations induced by collective oscillations of free electrons at the interface between metals and dielectrics
While manifestations of the same basic phenomenon, one can distinguish between two types of SPs: surface plasmon polaritons (SPPs) on metal films which are traveling waves, or standing waves composed of counter propagating SPPs [12], and local surface plasmons (LSPs) which are associated with excitations of individual nanoparticles [13]
We presented a new approach to excite SPPs on a flat metal film without restrictions of the incident illumination angle

Summary

Introduction

Surface plasmons (SPs) are electromagnetic excitations induced by collective oscillations of free electrons at the interface between metals and dielectrics. One excitation approach is attenuated total reflection (ATR) [12], in which a thin metal film is sandwiched by two different dielectric materials and light is incident with a specific angle relative to normal from the optically denser dielectric side so as to satisfy a phase matching condition Another approach is the use of gratings which can provide additional phase matching from the generation of integer multiples of the reciprocal lattice vector [8]. Finite-difference time-domain (FDTD) calculations [14,15] and detailed analysis reveal that SPPs with a high near-field enhancement and an ultra-narrow bandwidth can still be excited with a grating located far away from the flat thin film We believe that this approach for generating SPPs is fundamentally interesting and could be useful in many applications, e.g. in improving SERS sensing capabilities without the need of narrow band tunable lasers or laser line filters to block undesired light from an input laser source. The flat surface provides freedom to engrave additional patterns on the surface to achieve the better control of SPPs on that surface, e.g., bow-tie shapes

System description and working principles

Numerical analysis and results

Summary and conclusions