Tuning electron bunch with a longitudinally shaped laser to generate half-cycle terahertz radiation pulse

Abstract

We present a new scheme for the realization of ultrashort terahertz (THz) radiation pulses by electron beam with a frequency-chirped microbunching structure travelling in a tapered undulator. In this proposal, a longitudinally modulated laser pulse with a chirp rate in the instantaneous modulation frequency is obtained through the optical beating of dual-chirp pulses; then the chirped micro-structure is converted to a chirped density modulation on electron beams by the laser-electron interaction and dispersion effect; finally by sending this electron beam into a designed undulator, ultrashort pulse and broad-band THz radiation can be produced. Considering the fact that the density modulation of the electron beam is directly inherited from the shaped laser, the central frequency and chirp rate can be easily tuned by the optical elements. Numerical simulations confirm that radiation pulses with ultrashort duration can be generated from such a microbunched electron beam. This technique may open new research avenues for strong-field few-cycle THz photonics.