Patent ID: 8638824

Claim:
A method for generating coherent Smith-Purcell radiation, in which: an electrically conductive diffraction grating which is delimited laterally by two electrically conductive walls is used, and an electron beam, having determined speed and current density, is passed above the diffraction grating, between the walls delimiting a latter, with a view to producing the coherent Smith-Purcell radiation by interaction of the electron beam with the diffraction grating, characterised in that: the speed of the electrons is sufficiently low in order that, in a dispersion diagram, where a frequency is expressed as a function of a wave number, for a grating-beam combination, a straight line called a beam line (I) and representing the electron beam, intersects a portion (V) of a branch of a three-dimensional dispersion relationship of the diffraction grating, located in a first Brillouin zone, and corresponding to a fundamental mode of the diffraction grating, at a point (P) located outside a zone delimited by straight lines called respectively a forward light line and backward light line (III, IV), and the current density of the electron beam is sufficiently high to excite the fundamental mode of the diffraction grating which is radiated towards an outside thereof.