A strong-field THz light source based on coherent transition radiation at the Shanghai soft x-ray free-electron laser facility

The Shanghai soft x-ray free-electron laser facility has two lines of self-amplified spontaneous emission mode and seeding mode, providing electron beams with high charge, high energy and fs length. By utilizing the electron beams with these special characteristics, strong-field THz radiation can be generated through coherent transition radiation. An electron beam with a root-mean-square length of 50 fs compressed by a frequency beating laser pulse can generate broadband THz radiation from 0.1 to 8 THz, with a pulse energy of up to 690 μJ. In addition, an electron bunch train modulated by a frequency beating laser pulse can generate narrowband strong-field THz radiation from 0.1 to 15 THz, and the pulse energy can reach 71 μJ at 15 THz. The proposed method will effectively enhance the characteristics of the THz radiation source at the Shanghai soft x-ray free-electron laser facility, providing an excellent tool for measuring the longitudinal structures of the electron beam and advanced THz experiments. At the same time, under low relativistic electron beam energy, this method also provides a feasible solution for the compact strong-field THz source.