Local Excitation, Scattering, and Interference of Surface Plasmons

The aperture probe of a near--field optical microscope (``TNOM'' configuration) can act as a point source of surface plasmon (SP) polaritons on gold and silver films by means of its evanescent optical
field. SP excitation reveals itself by the emission of a pair of sharply confined crescent-shaped light beams oriented in the direction of the SP resonance angle; the excitation also gives rise to peculiar ``approach curves'' and interference-like intensity undulations in the scan images. These findings introduce a new way to study local-scale plasmon scattering phenomena. (Dept480)