AbstractsPhysics

In this thesis electromagnetic near fields in nanoscale structures are investigated. The optical near field is characterized by a strong presence of evanescent (non-radiative) waves which are significant only within the distance of the wavelength of light from the surface of a light emitting or scattering object. These waves play an essential role in the design and characterization of components for nanophotonics and exhibit phenomena not encountered in the conventional far-field optics. In this thesis, specific optical systems at sub-wavelength scale are studied. In two of them the electromagnetic field is assumed to be deterministic whereas in two other systems the random nature of light is considered. One specific aim of this work is to assess the role of partial polarization and partial spatial coherence in electromagnetic near fields. This type of analysis necessitates the coherence theory of general, non-planar, three-dimensional (3D) electromagnetic fields which has not been available until very recently. The new concepts of electromagnetic coherence theory for 3D fields, such as 3D degree of polarization, electromagnetic degree of coherence, and electromagnetic theory of coherent modes, are applied to study partial polarization and partial spatial coherence of random near fields. Furthermore, the first explicit 3D coherent-mode representation is derived for a certain type of electromagnetic fields. The topics which are included in this thesis are as follows: Transmission of partially polarized light through a scanning near-field probe tip, is studied in terms of the 3D degree of polarization. The enhanced transmission of light through a single sub-wavelength slit on a metal film is investigated, and the resonance behavior of its transmission spectrum is analyzed. The electromagnetic coherence theory is applied to study surface plasmon resonances in metallic nanocylinders, and their effect on the 3D degree of polarization, the electromagnetic degree of coherence, as well as on the electromagnetic energy transfer in the optical near field is assessed. Also the fluorescence resonance energy transfer (FRET) mediated by plasmon resonant metallic nanoparticles is addressed. Väitöskirjassa tarkastellaan sähkömagneettisia lähikenttiä nanorakenteissa. Optisille lähikentille on luonteenomaista vaimenevien (ei-säteilevien) aaltokomponenttien hallitseva vaikutus kokonaiskenttään. Vaimenevat aallot ovat merkittäviä vain alle valon aallonpituuden etäisyydellä kentän lähteestä ja niiden huomioiminen on olennaista tutkittaessa ja suunniteltaessa nano-optisia komponentteja. Lisäksi vaimenevista aalloista johtuen lähikentissä esiintyy optisia ilmiöitä, joita ei tavata kaukana lähteestä. Tässä työssä tarkastellaan sähkömagneettista kenttää tietyissä alle aallonpituuden mittakaavan rakenteissa. Kahdessa rakenteessa sähkömagneettinen kenttä oletetaan täysin deterministiseksi, kun taas kahdessa muussa rakenteessa kentän satunnainen luonne huomioidaan. Tämän työn eräs tavoite on tarkastella juuri satunnaisuuden ja erityisesti…