Experimental Verification of Radiation of Plasma Oscillations in Thin Silver Films

Abstract

Self-supported silver films were bombarded with 25-kev electrons to study the radiation of plasma oscillations in the films. A quartz spectrograph with a resolution of 10 m mu was used to record radiation from the film. The radiation spectra was found to consist of a rather sharp line at 330 plus or minus 10 m mu and a broad continuum at the long-wavelength side of the line; for the shorter wavelengths, the intensity falls rapidly to zero. The dependence of the intensity on film thickness was studied as an experimental test of whether the radiation was really caused by plasmons. Experimental results demonstrate that the dependence of the line intensity on thickness agrees with theoretical prediction; showing two maxima between 0 and 200 m mu thickness, the second one much lower than the first, and the minimum equal to zero between them, while the intensity of the continuum apparently shows another dependence on thickness. As a result it is demonstrated that plasmons really can radiate, and that in silver plasmons exist with h omicron ? = 3.75 plus or minus 0.1 ev. (B.O.G.)