Optical performance and metallic absorption in nanoplasmonic systems

Abstract

Optical metrics relating to metallic absorption in representative plasmonic systems are surveyed, with a view to developing heuristics for optimizing performance over a range of applications. We use the real part of the permittivity as the independent variable; consider strengths of particle resonances, resolving power of planar lenses, and guiding lengths of planar waveguides; and compare nearly-free-electron metals including Al, Cu, Ag, Au, Li, Na, and K. Whilst the imaginary part of metal permittivity has a strong damping effect, field distribution is equally important and thus factors including geometry, real permittivity and frequency must be considered when selecting a metal. Al performs well at low permittivities (e.g. sphere resonances, superlenses) whereas Au & Ag only perform well at very negative permittivities (shell and rod resonances, LRSPP). The alkali metals perform well overall but present engineering challenges.

Searching for better plasmonic materials

“…Because the field distribution in a material depends on " 0 and the loss depends on " 00 , performance metrics or quality factors for a plasmonic material are generally a function of both " 0 and " 00 . Considering that different applications can have different definitions for the quality factors [147][148][149][150][151], our discussion is focused on four major classes of plasmonic devices: LSPR based devices, SPP waveguides, TO devices and superlens. It is important to note that the following discussions are valid only in the range of frequencies for which " 0 is negative.…”

Damping of Plasmons of Closely Coupled Sphere Chains Due to Disordered Gaps

“…In between these two extremes the performance can be maximized within the limitations of the materials and fabrication techniques. The choice of material is quite important because the quality of plasmons is related to the ratio of the real and imaginary parts of the permittivity 10,11 . Most often, however, practical constraints dictate the material used -the alkalis have the lowest loss and hence excellent plasmonic quality, but gold is used in the majority of cases because it is chemically inert even though its optical performance is somewhat inferior.…”

Universal scaling of local plasmons in chains of metal spheres

“…We will explore a range of permittivity values by considering the metals Au, Ag, Al and K. These particular metals are chosen because previous studies have shown that they all have low damping for some regions, and they have quite different permittivity profiles [16]. Au is used extensively in plasmonics due to its chemical inertness, and yet it has very strong interband damping around the sphere resonance, requiring modes to be red-shifted to achieve reasonable performance.…”

“…2d. This may seem unusual but actually it is the most logical comparison since permittivity relates directly to the nature of the resonance [1,23], and we previously employed this strategy for a wide variety of plasmonic systems [16]. In the following sections we first provide a review of a dipole approximation and its application to the problem at hand.…”