Engineering of electromagnetic interactions in three-dimensional plasmonic metamaterials
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Field of nanoplasmonics study the interaction of light with nanoscale metallic structures and it possesses the great potential of being the key element in future, highly integrated, on-chip nanophotonic aevices. Several major breakthroughs have been demonstrated in the past decade regarding the utilization of plasmonics for purposes ranging from optical nanoantennas to enhanced biochemical sensing platforms. So far, studies are generally focused on two-dimensional (2D) arrangement of plasmonic nanostructures. However, engineering of materials in three dimensions (3D) by integrating different kinds of plasmonic resonances in multi-layers, offers additional degrees of freedom in our design space, resulting in remarkable effects This thesis research investigates the outcomes of the tailoring of electromagnetic interactions between multiple plasmonic structures in three-dimensions. We are mainly focused on a coherence phenomenon termed as Farro resonance. Farro resonances are generally studied in atomic physics, which occur due to an interference between multiple excitation pathways where a discrete resonant state is coupled to a broad continuum. Fano resonances are inherently linked to an atomic physics concept termed as Electromagnetically Induced Transparency (EIT). Recently, a plasmonic analogue of the EIT effect was proposed and drew great attention. Plasmon Induced Transparency (PIT) enables one to mimic the extremely dispersive spectral characteristics of EIT, on-chip and without any stringent requirements. In the first two parts of this work, we show that by a precise engineering of the near-field interactions of plasmonic elements, PIT effect can be carried simultaneously to multiple spectral domains. This effect has many potential applications ranging from enhanced non-linearities to novel optical communication systems. In the third part, we investigate a multi-spectral Fano resonant plasmonic structure's non-linear response by embedding a nanoscale Kerr medium to the design. We show that a unique set of effects can be achieved through the interplay of Fano resonances and embedded optical non-linearity. In the last part, we develop a unifying theory to describe Fano resonances in both purely plasmonic structures and also in other systems which are comprised of plasmonic structures coupled to molecular resonances. The developed theory provides an invaluable intuition to Fano resonances and their utilization in applications such as biosensing and spectroscopy.
Thesis (Ph.D.)--Boston University