  We investigate the far-field optical resonances of individual dimer
nanoantennas using confocal scattering spectroscopy. Experiments on a
single-antenna array with varying arm lengths and interparticle gap sizes show
large spectral shifts of the plasmon modes due to a combination of geometrical
resonances and plasmon hybridization. All resonances are considerably broadened
compared to those of small nanorods in the quasistatic limit, which we
attribute to a greatly enhanced radiative damping of the antenna modes. The
scattering spectra are compared with rigorous model calculations that
demonstrate both the near-field and far-field characteristics of a half-wave
antenna.
