Modelling of spectroscopic Mueller matrices of ordered nanoplasmonic surfaces using the finite element method
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- Institutt for fysikk 
This thesis is focused on modelling the complete polarization dependent optical response resulting from reflection from periodic nanostructures with a two-dimensional lattice, using the commercial software COMSOL Multiphysics based on the finite element method. An efficient model exploring the COMSOL wave optics module has been developed and the results have been successfully compared to the experimentally recorded Mueller matrices of plasmonic nanostructures previously manufactured in NTNU NanoLab. Three different samples have been targeted, consisting of plasmonic hemispheroidal nanoparticles in square or rectangular lattices on a SiO2 substrate. The size and shape of the nanoparticles were different for each sample. Their rich optical response, including localized surface plasmon resonances (LSPR), polarization coupling, and strong dependency on Rayleigh anomalies, were reproduced by the COMSOL model. A similar model was further used to simulate a sample of densely packed tilted GaSb cones for photon energies beyond its corresponding experimental work, revealing a strong polarization coupling around 7.5 eV. Model efficiency was optimized to greatly reduce computation time and memory requirements. Further optimization measures have been suggested that could vastly improve performance, which in turn would open up possibilities of modeling more complex and computationally demanding systems.