  The condition of phase matching prohibits the transfer of excitation from
free-space photons to surface plasmon polaritons (SPP). We propose and analyze
a scheme that excites an ensemble of emitters in a collective state, which is
phase matched with the SPP by the optical pulses used for its preparation. By a
collective enhancement the ensemble, hence, emits an SPP in a well defined
direction. We demonstrate the scheme by analyzing the launching of
near-infrared graphene SPP. Our theory incorporates the dispersive and
dissipative properties of the plasmon modes to evaluate the non-Markovian
emission by the ensembles and will also be applicable for other types of
surface polaritons.
