Oblique-incidence excitation of surface plasmon polaritons on small metal wires

TL;DR

This paper presents an experimental and theoretical study of surface plasmon polaritons on small metal wires at oblique incidence, introducing new fabrication and measurement techniques, and validating a scattering model for cylindrical wires.

Contribution

It introduces a novel experimental setup and fabrication methods for small metal wires, and compares measured SPP excitation with a new electromagnetic scattering model.

Findings

Good agreement between experimental data and scattering theory at low incident angles.

First oblique incidence measurements of SPP on small metal wires.

Validated the scattering model for cylindrical SPPs at higher incident angles.

Abstract

This work reports on the experimental investigation of surface plasmon polaritons (SPP) on cylindrical wires of small diameters. Applying a new technique that was developed by this group and recently reported, single wire and wire array samples of gold (Au) and silver (Ag) with small diameters 400nm < D < 3 mum and high aspect ratios <= 75000 in photonic crystal fibers and single hole capillaries are fabricated. Additionally, effective bulk metal wires of Au and Ag are created by a hybrid technique, including fiber tapering and magnetron sputter deposition for a large number of different diameters between 13 mum to 50 mum. The measurement of the absorption, corresponding to the excitation of SPP modes is realized with a new goniometer-based experimental setup for oblique incidence laser beam scattering at a single wavelength. A device is developed that allows a simultaneous measurement of the scattering amplitude in s- and p-polarization under varied incident angle. For comparison, a model for the dispersion of discrete SPP modes and their angles of excitation is derived. The computed results are for the first time compared with a theoretical approach to electromagnetic scattering theory for cylinders, that is calculated analogue to Mie scattering and to an exact solution of Maxwell's equations for cylindrical SPP. The validity of the model is proved for higher incident angles. The first oblique incidence examination of SPP on metal wires for this size range is reported. The experimental results for low incident angles show good accordance to the numerical results from scattering theory.