Optical Properties of Metallic Waveguide Structures at the Nanoscale

粒子等离激子和表面等离激子分别是金属粒子或金属表面电荷分布和电磁场的集体激发。金属的微观和纳米结构的最新进展使得等离子体的特性，特别是它们与光相互作用的方式，得到了前所未有的调整。这为使用结构金属作为纳米级光子学和电子设备的常见构建块提供了机会。金属中电荷激发对外部光场的响应是非局域的。这在技术上是由电荷激发运动方程中的梯度项得出的，最终是由于电荷守恒。虽然在整体系统中，这种非局域性通常可以忽略不计，但它在金属纳米结构中确实变得重要，因为它们的空间尺寸往往是几十纳米的数量级，最小的特征通常小于10纳米，因此引入了新的长度尺度，小于光的波长，在此基础上，必须考虑金属中的电荷分布以及电磁场，以便对此类系统中的动力学进行正确描述。此外，由于纳米结构系统中的电荷积累，强光场中的非线性响应效应增强。该项目的目标是利用数值技术对金属纳米结构中的非局部和非线性响应效应进行一致的微观描述。等离子体动力学的经典和量子力学模型将耦合到麦克斯韦方程组，使用时域有限差分格式处理。

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.