Elastische und inelastische Lichtstreuung an Edelmetall-Nanopartikeln und scharfen Goldspitzen

Within this work, single nanoparticle aggregates of gold, silver and copper, as well as sharp gold tips, are investigated with respect to their light scattering properties. The optical experiments on nanoparticle aggregates are intended to provide deeper insightinto the resonance behaviour of the aggregates, which are widely used as substrates for surface-enhanced Raman spectroscopy. With this aim, single particle aggregates prepared from colloidal solutions are investigated by measurement and correlation of the elastic white light scattering spectra and the inelastic luminescence spectra at different excitation laser wavelengths. These measurements are compared with quasi-static calculations of the extinction cross sections of the particle aggregates. Additionally, the SERS activity of single aggregates is compared with their resonance behaviour.
Luminescence spectra of sharp gold tips, which are applied for apertureless scanning
near-field optical microscopy, are measured at one- and two-photon excitation. These spectra provide information about the resonance behaviour of the tips. Moreover, the elastic light scattering at a sharp gold tip is used to probe the distribution
of the electric field strength in the focal region of a high NA parabolic mirror confocal
microscope in relation to the incident polarisation. A comparison of the measured intensity distributions with the theoretical results of vector field calculations shows that the calculated data are well reproduced by the light scattering measurements.