Focusing light on nanoscale: A novel plasmonic-lens design

Surface plasmons are oscillations of the conduction charges at a metal-dielectric interface. The symmetric mode of the surface plasmonic oscillation has no cut-off for propagation. A thin layer of dielectric sandwiched between two thick layers of metal can support plasmonic modes with large propagation constant and small group velocity. Further, surface plasmons can be easily excited by photons.;These attributes of the surface plasmons give way to the design of a circularly symmetric three dimensional nanoscopic structure that can be used to focus down the energy of a plasmon to a very small volume, much beyond the conventional diffraction limit. Analysis of metal-optics on the sub-wavelength scale using distributed circuit models of transmission lines establishes the equivalence of the plasmonic lens with two-dimensional tapered transmission line. This circuit level perspective brings forth several key insights that govern the nanoscale energy focusing, such as kinetic inductance and impedance transformation in two-dimensionally tapered parallel plate metal-dielectric-metal structures.;The fabrication of a plasmonic lens for focusing the energy poses several challenges. The three dimensional aspect of the design forces us to explore new methods of fabrication and metrological characterization, evaluate the repeatability and yield of several process steps, and finally the integration of these steps into a sequence with each step being compatible with all the other steps in the chain.;This dissertation also discusses the experimental set-up and data analysis of the near-field optical characterization of the plasmonic lens. The limitations of the measurement technique are detailed and this gives way to the suggestions of alternate diagnostics that can improve the characterization of the proposed plasmonic lens in future.