Theoretical investigation on a tunable free-electron light source

The concept and experimental results given in [1,2] are very interesting and attractive. Our paper presents detailed theoretical investigations on it and the results confirm that the mechanism of the light radiation experimentally detected in [1,2] is a special kind of diffraction radiation within a waveguide with nano-scale periodic structure excited by an electron beam. The numerical calculations based on our theory and digital simulations are well agreed with the experimental results. This mechanism of the diffraction radiation is of significance in physics and optics, and may bring good opportunity for the generation of electromagnetic waves from light to THz frequency regime.