Tomographic Plasmon Spectroscopy of a Single Gold Nanoparticle

We demonstrate a tomographic method for determining the degree of ellipticity and the orientation of a gold nanoparticle. To do this, we attach a single nanoparticle to the end of a sharp glass fiber tip and record its plasmon spectra for different incident polarizations and angles of incidence. Our measurements allow us to identify the plasmon spectra along the three main axes of the particle, therefore resolving its “internal” spectral inhomogeneity. Knowledge of the plasmon resonances and the orientation of a metallic nanoparticle is an important asset for controlled and quantitative studies of its interaction with a single molecule.