Simultaneous high-frequency Super-Radiance and low-frequency Coherent Spontaneous Radiation from ultrarelativistic electrons in a waveguide

Terahertz generation of high- and low-frequency pulses from an ultrarelativistic electron bunch, which move in a waveguide placed in an undulator, has been studied. If the length of the bunch is less than the low-frequency wavelength, its radiation under certain conditions stabilizes the length of the bunch and largely compensates for the velocity spread introduced by the particle repulsion. This leads to a significant improvement in the micro-bunching of electrons and increases the energy of the radiated high-frequency pulses.