  We report on a combined far- and near-field study of surface plasmon
polaritons on freestanding perforated gold films. The samples are fabricated by
focused ion beam milling of {a periodic hole array into} a carbon membrane
followed by thermal evaporation of gold and plasma ashing of the carbon film.
Optical transmission spectra show a series of characteristic features, which
can be attributed to the excitation of surface plasmon modes via the periodic
nanohole array. The corresponding near-field distributions are mapped by
electron energy-loss spectroscopy. Besides the optically bright surface plasmon
modes, we observe in the near-field an additional dark plasmon mode, which is
absent in the normal incidence far-field spectra. Our experimental results are
in good agreement with numerical computations based on a discontinuous Galerkin
time-domain method.
