Strong electron density modulation with a low-power THz source for generating THz superradiant undulator radiation

We propose a scheme to modulate a low-emittance electron beam at THz frequency using a low-power optical THz source (seed). In this scheme, a matching section introduces tunable angular dispersion and focusing to the electrons. It helps to slice the electrons into "energy layers" and largely cancels out the impact of uncorrelated energy spread on electron modulation. Analytical and numerical studies have been carried out to demonstrate the proposed scheme. It is found that a strong electron density modulation (bunching) over the frequency range from 1 to 6 THz can be achieved when the peak power of THz seed is no more than 1 kW. The bunched beam can be used to generate superradiant undulator radiation with the peak power of 10s MW.