  Plasmonic dark modes are pure near-field resonances since their dipole
moments are vanishing in far field. These modes are particularly interesting to
enhance nonlinear light-matter interaction at the nanometer scale because
radiative losses are mitigated therefore increasing the intrinsic lifetime of
the resonances. However, the excitation of dark modes by standard far field
approaches is generally inefficient because the symmetry of the electromagnetic
near-field distribution has a poor overlap with the excitation field. Here, we
demonstrate the selective optical excitation of bright and dark plasmonic modes
of single gold nanorods by spatial phase-shaping the excitation beam. Using
two-photon luminescence measurements, we unambiguously identify the symmetry
and the order of the emitting modes and analyze their angular distribution by
Fourier-space imaging.
