Surface plasmons in silver films-a novel undergraduate experiment H.J.Simon cillations in the electron density at the surface of a metal D. E.Mitchell J. G. Watson may be described in terms of these waves. onradiative surface plasma waves have been known Department of Physics and Astronomy as solutions o equations since Sommerfeld. The University of Toledo Toledo, Ohio 43606 uminum films in tota d by Turbadar; how (Received 17 October 1974; revised 21 January 1975) o surface ce plas- Surface plasmon phenomena are a topic of consi current interest. We describe a simple experiment and th ory for a senior level undergraduate investigation plasmons in silver evaporared on Light (p-polarized, the prism degrees greate sharp minimu sponding to t minimum in the refleci the resonant film. The dispersion re the reflectivity due to are calculated. Only a mo necessary to produce the required thin silver films. us and discuss n silver films evaporated at p We con- clude by suggesting extensions nt to study surface plas sion of the surface plasmon SURFACE PLASMON DISPERS We now derive a dispersion relation that will relate the propagation vector of a surface wave traveling along the INTRODUCTION surface of a metal to its angula We conside Surface plasma waves are transverse magnetic(TM) the space >0 to complex electromagnetic waves, traveling along the interface of dielectric function two different media. We will assume one of the media to dielectric constant for a be a metal and the other to be air. The waves propagete. The imaginary p ponentially attenuated in the normal direction in both the scribes the optical will assume metal and air. The wave vector,, of a surface plasmon surface plasmon on a semi-infinite dielectric bounded by vacuum is given <0 is as- by sumed to be air of he essentia assumption is to postulate the existence of only a single wave on each side of the b ectric fields are assumed to be m = ∈12 (1) E(x,2,t)=E k2(2) where e is the complex dielectric function of the medium at the angular frequency. For most metals∈a)is less The complete wave equation for this wave in each region than-1 in the visible region of the spectrum, and we see may now be written. Normally, in studying wave propa- from Eq. (1) that is greater than the wave vector of an gation in an infinite n electromagnetic wave in air at the same w. Surface plas- and ka to be give real numbers and uses the wave equation to determine the mon waves may be excited only with evanescent waves frequency of the propagating wave. Instead o this proce and are therefore classified as nonradiative. Collective os-dure, we assume that w is given and is a real number 6301 American Journal of Physics Vol. 43, No. 7, July 1975 Copyright 1975 by the American A.ssociation of Physics Teachers