On the Electron Emission from the Focal Region of a Symmetrically Convergent Surface Plasmonic Wave on the Free Surface
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CS OF SURFACES AND INTERFACES
On the Electron Emission from the Focal Region of a Symmetrically Convergent Surface Plasmonic Wave on the Free Surface of a Metal Film A. B. Petrin* Joint Institute for High Temperatures, Russian Academy of Sciences, Moscow, 125412 Russia *e-mail: [email protected] Received February 27, 2020; revised February 27, 2020; accepted March 15, 2020
Abstract—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. Keywords: nanophocusing, surface plasmons, optical sensors DOI: 10.1134/S0030400X20080287
INTRODUCTION AND STATEMENT OF THE PROBLEM Recently, theoretical methods for studying excitation of surface waves by confined light beams in the Kretschmann geometry have been actively developed. In particular, the nonlocality of reflection accompanied by excitation of surface waves was revealed [1]. The performed studies made it possible to explain theoretically the Goos–Hänchen effect, which manifests itself in splitting of the reflected wave [2], and to consider interference of surface waves [3]. Then, the scheme for optimal focusing of a surface wave converging to a point on a surface was developed and the electric-field distribution at the surface focus was calculated [4]. In this study, the results obtained are used to consider theoretically the electron emission stimulated by an optical wave in the focal region. The phenomenon of electron emission from the metal-film surface stimulated by a surface plasmonic wave was observed experimentally in [5, 6]. However, the possibility of focusing a surface plasmonic wave on the free surface of a metal film would allow one to obtain optically stimulated electron emission from local regions on the surface. Moreover, we can suggest that, due to the extremely strong dependence of the emission-current density on the field strength on the surface, this region of surface electron emission can be much smaller than
the light wavelength. This circumstance would make it possible, e.g., to investigate the emitting ability of the film surface with high resolution or to design special localized electron-emitting sources for electron–optical systems. The purpose of this study was to analyze the abo
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