Enhancement of a coherent (super-radiant) emission in FEL by means of energy modulation of an emitting short electron bunch

Super-radiant emission from a wiggling short electron bunch, is strongly suppressed at high frequencies in comparison with radiation, obtained in a FEL if an ultra-short e-beam pulse of the same total charge is available. However, radiation intensity of a wiggling short electron bunch can be greatly enhanced by means of energy modulation. In this way, a super-radiant FEL source driven by short electron bunches and operating in the Tera-Hertz regime can be realized. Analytical evaluations and numerical simulations utilizing a space-frequency 3D model show, that a linear energy modulation enables one to increase the power of super-radiant emission by few orders of magnitude. Possible limitations in application of this method are also discussed, as well as a spectral purity of enhanced radiation.