FEMTOSECOND TUNNELING RESPONSE OF SURFACE-PLASMON POLARITONS

We obtain femtosecond (200 fs) time resolution using a scanning tunnel ing microscope on surface plasmon polaritons (SPPs) generated by two 1 00 fs laser beams in total internal reflection geometry. The tunneling gap dependence of the signal clearly indicates the tunneling origin o f the signal and suggests that nanometer spatial resolution can be obt ained together with femtosecond temporal resolution. This fast respons e, in contrast to the picosecond decay time of SPPs revealed by differ ential reflectivity measurements, can be attributed to a coherent supe rposition of SPPs rectified at the tunneling junction. (C) 1998 Americ an Institute of Physics. [S0003-6951(98)02223-2].