Interference of surface plasmon polaritons from a point source

The interference patterns of the surface plasmon polaritons(SPPs) on the metal surface from a point source are observed. These interference patterns come from the forward SPPs and the reflected one from the obstacles, such as straightedge,corner, and ring groove structure. Innovation to the previous works, a point SPPs source with diameter of 100 nm is generated at the freely chosen positions on Au/air interface using near field excitation method. Such a point source provides good enough coherence to generate obvious interference phenomenon. The constructive and destructive interference patterns of the SPPs agree well with the numerical caculation. This point SPPs source may be useful in the investigation of plasmonics for its high coherence, deterministic position and minimum requirement for the initial light source.