Optical fiber tip excites surface plasmons on thick metal film

Scientists from the University of Munich (Munich, Germany) report that two-dimensional surface plasmons on a thick metal film can be locally excited using a near-field optical-fiber tip. Because the plasmons are longitudinal waves, light polarization controls the direction in which they are launched on the metal surface. This phenomenon has allowed the researchers to, in a sense, "play golf" with surface plasmons on a metal film perforated with nanometer-sized holes. When the near-field optical fiber tip is located next to a nanohole, the surface plasmons only reach the nanohole when the electric-field vector points to the hole. The arrival of the surface plasmon in the hole is detected by sensing its reradiation on the other side of the metal film with a photodiode. By placing several nanoholes in a circle, it may be possible to optically address specific holes just by changing the light polarization, the researchers believe. Their experiments show that surface plasmons on specifically nanostructured metal films might scale down optical devices to the nanometer world. Contact Jochen Feldmann at [email protected].