Measuring the speed of a surface plasmon

Abstract

This paper presents experiments using an 800-nm pulsed laser and a streak camera with 2-ps resolution, which is implemented with a two-fiber differential measurements permitting a 0.2-ps resolution. With this technique, we measure the speed of the propagation of the surface plasmons. This velocity was found to be approximately $(0.57\mathrm{}\pm 0.19)c,$ about 61% the value expected from simple theory (i.e., about $0.94c).$ The former result may clarify what is going on at the metal vacuum interface excitations, and has been measured by a direct method without the need for any theory.