Plasmonic effects in nanosized particles enhance the interaction between light and matter due to the localized surface plasmon resonance, with potential applications such as all-optical transistors and optical computers. Commonly, the dynamics of nanoparticles’ optical properties are assessed via pump-probe spectroscopy, where a plasmonic structure is exited by an initial laser, the pump. Thereafter a second, less intense laser, a probe, interacts with the now excited structure at a time delay. Through measurements of the probelight transmitted by the matter, the optical dynamics of the structure are monitored. Similar methodologies can potentially be used for other applications as well, such as all-optical switching. This study focuses on an implementation of a numerical finite element method model simulating a pump-probe experiment to predict the effects of different geometries and evaluate experimental data. The simulations are split into three parts. Initially, periodically spaced nanoparticles are excited by the pump laser. Then the model estimates the internal thermal dynamics of the excited nanoparticles and in turn, determines the change in complex permittivity. Lastly, the probe-matter interaction is modeled. To evaluate the model, a comparison with another model was performed. Furthermore, simulations of periodically spaced gold dimer nanoparticles in air were done to investigate how dimers affect transmitted light. For a probe light polarization rotated 45◦ against the axis parallel to the dimer, a change in rotation of 6◦ over 35 fs was induced by the pump, indicating a potential switching mechanism.

This study is comprised of two separate parts: (1) modeling thermochemical nonequilibrium processes, and (2) flow field simulations of spark-induced plasma. In the first part, the methodology and literature for modeling thermochemical nonequilibrium processes in partially ionized air is presented and implemented in a zero-dimensional solver, termed as NEQZD. The solver was verified for a purely reacting flow case as well as two thermochemical nonequilibrium flow cases. A three-temperature electron-electronic model for thermochemical nonequilibrium partially ionizing air mixture was implemented and demonstrated the ability to capture additional physics compared to the legacy two-temperature model through the inclusion of electronic energy nonequilibrium. In the second part of this work, full scale axisymmetric simulations of the flow field produced by the abrupt heat release of spark-induced plasma were presented and analyzed for two electrode configurations. The heat release was modeled based on data from experiments and assumed that all electrical power supplied to the electrodes is converted to thermal energy. It was found that steeper electrode walls lead to a greater region of hot gas, a stronger shock front, and slightly larger vortices.