Tunable Surface Plasmon Dynamics

Abstract

Due to their extreme spatial confinement, surface plasmon resonances show great potential in the design of future devices that would blur the boundaries between electronics and optics. Traditionally, plasmonic interactions are induced with geometries involving noble metals and dielectrics. However, accessing these plasmonic modes requires delicate election of material parameters with little margin for error, controllability, or room for signal bandwidth. To rectify this, two novel plasmonic mechanisms with a high degree of control are explored: For the near infrared region, transparent conductive oxides (TCOs) exhibit tunability not only in "static" plasmon generation (through material doping) but could also allow modulation on a plasmon carrier through external bias induced switching. These effects rely on the electron accumulation layer that is created at the interface between an insulator and a doped oxide. Here a rigorous study of the electromagnetic characteristics of these electron accumulation layers is presented. As a consequence of the spatially graded permittivity profiles of these systems it will be shown that these systems display unique properties. The concept of Accumulation-layer Surface Plasmons (ASP) is introduced and the conditions for the existence or for the suppression of surface-wave eigenmodes are analyzed. A second method could allow access to modes of arbitrarily high order. Sub-wavelength plasmonic nanoparticles can support an infinite discrete set of orthogonal localized surface plasmon modes, however only the lowest order resonances can be effectively excited by incident light alone. By allowing the background medium to vary in time, novel localized surface plasmon dynamics emerge. In particular, we show that these temporal permittivity variations lift the orthogonality of the localized surface plasmon modes and introduce coupling among different angular momentum states. Exploiting these dynamics, surface plasmon amplification of high order resonances can be achieved under the action of a spatially uniform optical pump of appropriate frequency.