Electromagnetic fields in nanoscale structures : effects of polarization and spatial coherence

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.; Vaitoskirjassa tarkastellaan sahkomagneettisia lahikenttia nanorakenteissa. Optisille lahikentille on luonteenomaista vaimenevien (ei-sateilevien) aaltokomponenttien hallitseva vaikutus kokonaiskenttaan. Vaimenevat aallot ovat merkittavia vain alle valon aallonpituuden etaisyydella kentan lahteesta ja niiden huomioiminen on olennaista tutkittaessa ja suunniteltaessa nano-optisia komponentteja. Lisaksi vaimenevista aalloista johtuen lahikentissa esiintyy optisia ilmioita, joita ei tavata kaukana lahteesta. Tassa tyossa tarkastellaan sahkomagneettista kenttaa tietyissa alle aallonpituuden mittakaavan rakenteissa. Kahdessa rakenteessa sahkomagneettinen kentta oletetaan taysin deterministiseksi, kun taas kahdessa muussa rakenteessa kentan satunnainen luonne huomioidaan. Taman tyon eras tavoite on tarkastella juuri satunnaisuuden ja erityisesti…