Surface plasmons at single nanoholes in Au films

The generation of surface plasmon polaritons (SPPs) at isolated nanoholes in 100 nm thick Au films is studied using near-field scanning optical microscopy. Finite-difference time-domain calculations, some explicitly including a model of the scanning tip, are used to interpret the results. We find the holes act as point-like sources of SPPs and demonstrate that the interference between the SPP and a directly transmitted wave allows determination of the wavelength, phase, and decay length of the SPP. The near-field intensity patterns can be manipulated by varying the angle and polarization of the incident beam.