Field enhancement in a circular aperture surrounded by a single channel groove

Nicolas Bonod,Evgeny Popov,Davy Gérard,Jerome Wenger,Hervé Rigneault

doi:10.1364/oe.16.002276

Abstract

Numerical analysis of diffraction by a single aperture surrounded by a circular shallow channel in a metallic screen shows the possibility of a 50-fold increase of the electric field intensity inside the central aperture, when compared to the incident field. Detailed analysis of cavity modes and their coupling through surface plasmon wave determine the parameters leading to maximum field enhancement. This effect can be used in high-efficiency single-molecule fluorescence analysis in attoliter volumes.

Highlights

Light transmission through single or periodically arranged apertures has attracted the interest of scientists, at first, due to the possibility to confine the electromagnetic field into a relatively small region, smaller than the diffraction limit in free space, generating evanescent wavevectors, leading to increased resolution in optical microscopy [1,2,3]
The simultaneous excitation of cavity modes in the central aperture and in the surrounding coaxial channel can lead to almost 50-fold increase in the electric field intensity in the central aperture, compared to the intensity of the incident field
The coupling between the two cavities is made through the surface plasmon wave that propagates along the metal-cladding interface

Summary

Introduction

Light transmission through single or periodically arranged apertures has attracted the interest of scientists, at first, due to the possibility to confine the electromagnetic field into a relatively small region, smaller than the diffraction limit in free space, generating evanescent wavevectors, leading to increased resolution in optical microscopy [1,2,3]. The aim of this paper is to study the possibility of field enhancement by using the combined effect of simultaneous excitation of cavity resonances inside the aperture and in a surrounding channel groove, coupled through the surface plasmon wave. This triple interaction results in 30-50 fold field enhancement in the opening of the central aperture. To this aim, it is sufficient to use a single channel of about one wavelength diameter, i.e., enabling strong focusing of the incident beam down to the diffraction limit.

Intensity enhancement – effect of the channel

Cavity resonances inside the channel

The choice of the channel inner wall

The role of the channel external wall

Findings

Conclusion