On the electron emission from the focal region of a symmetrically convergent surface plasmonic wave on the free surface of a metal film

Excitation and focusing of a radially convergent surface plasmonic wave on the free surface of a gold film in the Kretschmann geometry have been considered based on the theory of reflection of a plane electromagnetic wave from a plane-layered structure. The electric-field distribution in the vicinity of the focus on the free film surface has been quantitatively investigated. Based on this distribution and the theory of thermally-assisted field electron emission from a metal, the time-averaged electron-emission current has been estimated in dependence of the amplitude of the normal component of the wave electric field at the focal-distribution center. It is shown that the major part of the emission current originates in the region near the focal center with a diameter of about a tenth of the operating wavelength in vacuum; the emission current originating from the diffraction rings around the central maximum is negligible.