Abstract

Recently, it has been shown that different types of metallic nanostructures may exhibit total light absorption. To achieve the total light absorption effect, an intrinsic resonance associated with either delocalized excitations (e.g., surface plasmons [1]) or localized excitations (e.g., plasmons in nanopores [2]) should be excited in the metallic nanostructure. Although the nanostructures that exhibit total light absorption may differ considerably, they seem to possess some common characteristics: (i) light transmission through the entire structure is forbidden, (ii) the total light absorption arises as a plasmon resonance, and (iii) the total absorption is achieved at a specific condition involving a coefficient of coupling between the plasmons and electromagnetic radiation (critical coupling condition). Here we optical properties of a metallic nanostructure in terms of the equivalent oscillating-current resonant circuit, which explains the total light absorption phenomenon in different plasmonic nanostructures on the same basis. This model is illustrated by considering two different types of nanostructures, a two-dimensional lattice of metallic spheres and the inverted structure that is a two-dimensional lattice of nanovoids in metal, which are described by two different basic equivalent RLC resonant circuits: series-resonant circuit and parallel-resonant circuit, respectively. We conclude that total light absorption results from matching the free-space impedance to the surface impedance of the nanostructure at the plasmon resonance

© 2007 IEEE