Experimental Investigation of the Interaction Radiation of a Moving Electron with a Metallic Grating: The Smith-Purcell Effect

Abstract

In order to test a previously proposed theory of the Smith-Purcell effect, experimental results for the linewidth, the radiation patterns, and the absolute emitted power from aluminium and silver gratings are reported. The measurements are made at 130 kV in the ultraviolet and visible range with gratings of 1221.2 lines/mm. For this purpose, we recall the theoretical formulas for the power and the line breadth as a function of the incidence angle of the electrons on the grating: These two quantities characterize the emission mechanism. We then show briefly how various experimental parameters can affect the results. We thus deduce that the observed radiation does indeed arise from the process initially proposed (i.e., diffraction of the electron field). The line breadth agrees well with the theory. With the assumption that the average groove profile is close to that claimed by the manufacturer (in fact the grooves appear irregular in electron-microscope measurements) the theory accounts for the main features of the observed dependence of the power and radiation patterns upon the wavelength and the metal. Numerical calculations of the influence of the profile show that within the experimental error the theory satisfactorily predicts the absolute emitted power. A rise in intensity is measured at the surface plasma wavelength for Ag; this is in agreement with the theory.