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Hartmann, Nicolai (2013): Coupling of emitters to surface plasmons investigated by back focal plane microscopy. Dissertation, LMU München: Fakultät für Chemie und Pharmazie



Current efforts in the field of plasmonics towards device integration and miniaturization require detailed knowledge about the coupling between surface plasmons and emitters. In this work coupling between surface plasmon polaritons and different emitter systems has been investigated by the technique of back focal plane imaging. To develop a deeper understanding of the interaction phenomena the studies focused on single emitters in elementary plasmonic configurations that allow for an analytical description. The first part of the thesis reports on the successful demonstration of surface plasmon polaritons launched by a single dipolar carbon nanotube emitter on a metal thin film after local optical excitation. Leakage radiation microscopy images, recorded in the back focal plane of a microscope objective, could be modeled successfully and contained the propagation length and direction of surface plasmon polaritons. Corresponding real-space images revealed plasmon propagation away from the single dipolar plasmon source. The polarization behavior of surface plasmon polaritons launched by single carbon nanotubes was found to be radial as predicted by theoretical calculations. Remote excitation of single walled carbon nanotube excitons via propagating surface plasmons is demonstrated in the second part. A scanning aperture probe was used as source for propagating surface plasmons with fine controllability over excitation position and propagation direction. It was raster scanned in close proximity over a single carbon nanotube located on a metal film while recording the emission response from the nanotube. The carbon nanotube showed an emission response while the aperture plasmon source was still far away from the nanotube position. Theoretical modeling of the excited surface plasmon fields confirmed that the nanotube maps the surface plasmons locally with sub-diffraction resolution. In the last part, radiation channels in the vicinity of a plasmonic nanowire were investigated. Radiation patterns of a coupled system of rare earth nanocrystals and silver nanowires in the back focal plane revealed that the emission in the vicinity of a nanowire can be approximately described by two emission channels that can be calculated analytically: Dipolar emission, also observed in the absence of the nanowire, and leakage radiation from the nanowire. The latter can be calculated using an antenna-resonator model that considers the air-dielectric interface on which the nanowire is deposited and the position of excitation along the nanowire. Fitting of the experimentally observed patterns provides estimates for the branching ratio between the two emission channels and further enable the determination of the plasmon wave-vector supported by the nanowires.