UC San Diego

The confinement of light in cavities that are smaller than the optical diffraction limit can be achieved through the use of metallic nanoparticles by exploiting their optical properties. Two geometries were studied for their different capabilities of light xii confinement. First, a bowtie nanojuction which provides high localization to the gap created between two triangular prisms. Second, a metal -insulator-nanoparticle sandwich structure which localizes light to the gap between two metal films. Simulations were widely utilized to model the optical properties of each geometry. For bowtie antenna finite element method (FEM) was used to model the effect of defects that occurs as the result of nanoparticle synthesis or the assembly into bowties. It was found that defects have the ability to shift the resonant wavelength by as much as 200 nm. Bowtie junctions also demonstrated defect tolerance with respect to the near-field enhancement providing evidence that they will be viable structures for nanophotonic and nanoplasmonic applications. For the sandwich structure, also known as a nanocube metasurface, finite difference time domain (FDTD) was used to model the plasmonic mode structure of the metasurface. Through simulation and experimental findings it was found that the metasurface provides nearly perfect absorbance at its resonant frequency, confining the light to nanoparticle- nanoparticle gaps, and the nanoparticle-film gap. The addition of a gain medium to the insulating spacer layer is also being explored. It holds promise for fluorescence enhancement and sensing applications