Public defence in Engineering Physics, M.Sc. (Tech) Jani Taskinen

Title of the thesis: Light-matter interactions and topological effects in ensembles of plasmonic nanoparticles

Doctoral student: Jani Taskinen
Opponent: Associate Professor Jan Klärs, University of Twente, The Netherlands
Custos: Professor Päivi Törmä, Aalto University School of Science, Department of Applied Physics

Light has always been one of the most important tools of modern society, and the constant demand for miniaturization in our everyday devices has driven the creation of smaller and smaller optical components. The field of plasmonics, which studies how light interacts with metal surfaces, may provide solutions to such demands. Modern nanofabrication methods can be used to construct nanoscale metallic structures that allow light to be confined into volumes smaller than its wavelength. Optical modes in such plasmonic structures are highly efficient in interacting with nearby particles, and combining them with light-emitting molecules allows for instance the creation of nanoscale laser sources.

In this doctoral thesis, 2D metallic devices were developed to study a relatively recent topic emerging in the field of nano-optics -- topological photonics. It is concerned with optical properties and modes that remain unchanged in the face of device imperfections, making it an exciting field of research focused on improving device robustness. Here we focused on the topological properties of the polarization state of light, which could be used as an additional way of transferring information via light.

Plasmonic nanostructures were used to generate optical modes and light sources with topological properties. Unlike typical optical components made from non-conductive materials, plasmonic devices are lossy in nature since light fields heat up the small metal structures. We showed that these inherent energy losses are a source of features related to topological properties in optical devices. The other, more applicable result of the thesis was the development of nanostructure geometries that could generate laser beams with topological polarization features, which hold great promise for data transfer applications. These results provide us with a better understanding of the nature of plasmonic phenomena, and they also demonstrate the advantages of taking topological aspects into account in the design of nano-optical devices.

Thesis available for public display 10 days prior to the defence at: https://aaltodoc.aalto.fi/doc_public/eonly/riiputus/ 

Doctoral theses of the School of Science: https://aaltodoc.aalto.fi/handle/123456789/52