  We develop a concept of surface plasmon polaritons (SPPs) based four-wave
mixing (4WM), in which a laser-launched evanescent SPP field is utilized as a
coherent pumping source to involve directly in a nonlinear 4WM process at the
dielectric/metal interface. Conversion efficiency of the resulting 4WM
radiation is expected to be dramatically increased due to the local-field
enhancement effect. Feasibility of implementing this concept at the air/gold
film and graphene flake/gold film interfaces is further examined by numerical
simulations. The concept shows intriguing promise for applications in newly
emerging nanophotonics, optoelectronics, and active plasmonics.
