ELECTROMAGNETIC WAKE IN THE SMITH-PURCELL CONFIGURATION

The radiation from the surface charge induced by the electrons passing over a metal grating, which is commonly called the Smith-Purcell (SP) radiation, is identified as an electromagnetic wake which is converted from the velocity component of the Lienard-Wiechert fields of the electron at the grating surface. It is shown that the electromagnetic wake can account for at most one millionth of the measured power. Further, the wavelength, spectral width, harmonic characteristics, and polarization of the electromagnetic wake does not match experimentally observed radiation in the SP configuration. It is demonstrated that the SP radiation is a free-electron two-quantum Stark (FETQS) emission. The reason why the FETQS emission is extraordinarily (e.g., 10(19) times) stronger than expected with quantum electrodynamics (QED) is explained based on the difference between an incident photon treated in QED and a classical periodic field to which 'phase' applies.