MacDonald, K.F., Krasavin, A.V., Soares, B.F., Bashevoy, M.V., Jonsson, F. and Zheludev, N.I.
Nonlinear plasmonics in a gallium/aluminium nano-composite
At QEP-17 at Photon06.
04 - 07 Sep 2006.
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We report the discovery of a highly nonlinear material structure that supports surface plasmon-polariton (SPP) waves. It is generally perceived that nonlinear SPP propagation regimes are difficult to achieve because SPP's are localized between two low-nonlinearity media - a highly transparent dielectric and a metal.
Here we show that a structural transformation in the metal provides a strong, reliable nonlinear response mechanism that affects and enables 'active' control of SPP propagation.
The material structure is a self-assembled nanoscale composite comprising a polycrystalline aluminium film (on a silica substrate) wherein the grain boundaries between aluminium domains and the aluminium/silica interface are infiltrated with nanolayers of gallium. A substantial change in this material's electronic and optical properties is provided by a reversible excitation-induced shift in the equilibrium between gallium's solid and liquid phases, while the framework of microscopic aluminium domains maintains the stability of the structure.
It is well suited to nonlinear switching contrast: the SPP decay length in liquid gallium (5-20 plasmonic applications such as the active control of SPP propagation because the excitation-induced transition in gallium is surface-driven and provides very good µm at visible and near-IR wavelengths) is approximately ten times longer than in solid gallium. The formation of the gallium/aluminium composite has been investigated using Electron Backscatter Diffraction and its ability to control SPP waves with sub-ns response and sub-µs relaxation times demonstrated in experiments based on the Otto configuration for SPP wave excitation, and on metal/dielectric micro-gratings (prepared by photolithography) designed to couple light to/from SPP's.
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