Observation of coherent Smith-Purcell radiation from short-bunched electrons

Abstract

Coherent Smith-Purcell radiation, generated by the passage of short-bunched electrons of relativistic energy of 42 MeV above the surface of a metallic grating, has been observed in the wavelength region from 0.5 to 4.0 mm. The intensity of the radiation is proportional to the square of the beam current. The intensity at \ensuremath{\lambda}=2.5 mm is enhanced by several orders of magnitude compared with the incoherent radiation. It is found that the intensity decreases proportionally to the square of the modified Bessel function [${\mathit{K}}_{0}$(2\ensuremath{\pi}h/\ensuremath{\lambda}\ensuremath{\beta}\ensuremath{\gamma})${]}^{2}$, as the beam height h from the surface of the grating increases.