Applications of principal modes to imaging, control and surface enhancement in nanoparticles

Student thesis: Doctoral Thesis

Abstract

The theory of principal modes allows a computationally efficient generalisation of Mie's analytical approach for the sphere to obtain semi-analytical solutions for general geometries with smooth surfaces. In this thesis, we apply this method to investigate a range of single and multiple particle metallic structures in the linear, non-linear and non-local response regimes outside of the quasi-static limit. We propose schemes for the coherent control of light waves and currents in metallic nanospheres, using conventional laser sources, in all three of these regimes.The conditions on the external control field we derive lead to a reduction of absorption, suppression of radiative losses and high sensitivity to small variations in the local environment, including subwavelength spatial shifts. As part of an international collaboration with researchers from Waseda University and the Institute for Molecular Science in Japan, the optical properties of single gold nanodiscs were studied by scanning near-field optical microscopy.The modal analysis indicates that the complex spatial features observed in the transmission images originate mainly from a few fundamental plasmon modes of the discs. By reformulating the principal modes in terms of Green'€™s functions we are able to describe systems containing multiple particles, in which both particles and host medium may be inhomogeneous. Using this formalism, the enhancement of the rates of both the emission and far field radiation of dipoles placed in the gap between metallic nanorods, nanospheres, and substrates are investigated numerically.For aluminium structures, bright mode resonances are tunable over tens or hundreds of nanometres in the ultraviolet by changing the size of the nanoparticles, with far field radiative enhancements of up to three orders of magnitude. These results show that aluminium nanostructures are ideal for applications to nano lasing and label-free detection of weakly fluorescent DNA bases and proteins in the ultraviolet.
Date of Award1 Feb 2016
LanguageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorFrancesco Papoff (Supervisor) & Benjamin Hourahine (Supervisor)

Cite this