Optical Manipulation of Relativistic Electron Beams using THz Pulses
  There are implementations and proposals for using microwave or optical radiation for electron acceleration, undulation, deflection, and spatial as well as temporal focusing. Using terahertz (THz) radiation in such applications can be superior to microwave or optical radiation since THz pulses can be generated with significantly smaller temporal jitter to the electron bunch to be manipulated as compared to microwave pulses, and contrary to the optical pulses, the much larger wavelength of THz pulses compares well with typical sizes of electron bunches. Recently generation of ultrashort THz pulses with 1 MV/cm focused electric field was demonstrated, and it is predicted that THz pulses with even 100 MV/cm focused field will be possible. According to the first results of our analytical and numerical studies this field strength is high enough for manipulation of relativistic electron beams by polarised THz pulses in various geometries. It is possible, e.g., to construct a 30 cm long THz undulator for saturated FEL working at 9.6 nm wavelength using electron bunches with 100 MeV energy and 0.42 nC charge. 
J. Hebling, J. A. F\"ul\"op, M. I. Mechler, L. P\'alfalvi, C.   T\H{o}ke, G. Alm\'asi
physics.acc-ph physics.optics