Thesis supervisor: Viktor Palm ja Ilmo Sildos (UT)
Opponent: Sergey K. Sekatskii (University of Lausanne).
The thesis in the rapidly developing field of nano-optics concerns light sources and light guides. Tiny light sources can be applied e.g. for visualizing of diffusion processes, in material science, biology and medicine. Optical fibers of sub-wavelength diameters can also be applied in different domains from material science to information technology.
One of the work tasks concerned the development of a new technological approach to production of diamond-based nanoscopic light sources and application of the light generated by such sources for investigation of optical fiber properties.
The elaborated light source is to be based on defect centers in nanodiamond particles. By introducing a defect center in a diamond nanoparticle, the originally transparent material becomes photoactive. If excited by light, the defect center starts to emit (infra)red light. The achieved properties of developed materials can be considered as a step ahead towards the new technology for industrial manufacturing of nanodiamond markers.
Another major part of the work concerns the light transmitted by optical fibers terminated by a metal-coated tapered tip with a subwavelength aperture. In the case of a bare (non-coated) nanofiber, the light starts to propagate outside the fiber material and is affected by the environment; the metal coating thus allows restricting the investigation to the light propagating inside the fiber. The very low transmission efficiency is a well-known feature of nanofibers. A finding of this work was that the transmission is frequency-dependent, which results in a spectral modulation of the transmitted light. It was also found that the metal-coated nano-tip contribution to the modulation is much larger and of opposite sign compared to the contribution of the bare fiber of the same length, which is considered as being a result of light interaction with metal coating.