Optical Properties of Metallic Waveguide Structures at the Nanoscale

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Particle plasmons and surface plasmon polaritons are collective excitations of charge distributions and the electromagnetic field in metal particles or at metallic surfaces, respectively. The recent progress in micro- and nano-structuring of metals allows an unprecedented tailoring of the plasmon properties, in particular the way they interact with light. This opens an opportunity to use structured metals as common building blocks of photonics and electronics devices at the nanoscale. The response of the charge excitations in a metal to an external light field is nonlocal. This results technically from gradient terms in the equations of motion of the charge excitations and is ultimately due to the conservation of charge. While in bulk systems this nonlocality is, in general, negligible, it does become important in metallic nano-structures, because their spatial dimensions tend to be of the order of a several tens of nanometers with smallest features often smaller than 10 nm and, thus, introduce new length scales, smaller than the light wavelength, on which the charge distributions in the metal as well as the electromagnetic fields must be considered in order to obtain a correct description of the dynamics in such systems. Furthermore, nonlinear response effects in strong optical fields become enhanced due to charge accumulation in the nanostructured systems. The goal of this project is to develop a consistent microscopic description of nonlocal and nonlinear response effects in metallic nano-structures using numerical techniques. Classical and quantum mechanical models of plasmon dynamics will be coupled to Maxwell's equations, which are treated using the finite-difference time-domain scheme.