Influence of excitation and collection geometry on the dark field spectra of individual plasmonic nanostructures.

Dark field microspectroscopy is the primary method for the study of plasmon modes of individual metallic nanostructures. Light from a plasmonic nanostructure typically scatters with a strong angular and modal dependence, resulting in significant variations in the observed spectral response depending on excitation and collection angle and polarization of incident light. Here we examine how spectrally dependent radiation patterns arising from an individual plasmonic nanoparticle, positioned on a dielectric substrate, affect the detection of its plasmon modes. Careful consideration of excitation and collection geometry is of critical concern in quantitative studies of the optical response of these nanoparticle systems.