Determination of Surface-Plasmon Dispersion Relation by Ricochet Photoemission

Photoelectrons emitted along a metal surface from atoms located at a small distance outside that surface have a high probability to ricochet with the excitation of a surface plasmon if the angle of emergence α is less than a critical angle αM. The line shape of the surface-plasmon satellite I₁(εₖ,α) peaks strongly at α=0 and presents another peak at α=αM. Experiments are suggested to locate the second peak and thereby determine αM(εₖ), a function which should yield direct information on the form and the parameters of the surface-plasmon dispersion relation.