  We experimentally demonstrate synthesis and in-situ analysis of multimode
plasmonic excitations in two-wire transmission lines supporting a symmetric and
an antisymmetric eigenmode. To this end we irradiate an incoupling antenna with
a diffraction-limited excitation spot exploiting a polarization- and
position-dependent excitation efficiency. Modal analysis is performed by
recording the far-field emission of two mode-specific spatially separated
emission spots at the far end of the transmission line. To illustrate the power
of the approach we selectively determine the group velocities of symmetric and
antisymmetric contributions of a multimode ultrafast plasmon pulse.
