Few-Cycle Pulse Generation in an X-Ray Free-Electron Laser

A method is proposed to generate trains of few-cycle x-ray pulses from a free-electron laser (FEL) amplifier via a compact afterburner'' extension consisting of several few-period undulator sections separated by electron chicane delays. Simulations show that in the hard x ray (wavelength similar to 0.1 nm; photon energy similar to 10 keV) and with peak powers approaching normal FEL saturation (GW) levels, root mean square pulse durations of 700 zs may be obtained. This is approximately two orders of magnitude shorter than that possible for normal FEL amplifier operation. The spectrum is discretely multichromatic with a bandwidth envelope increased by approximately 2 orders of magnitude over unseeded FEL amplifier operation. Such a source would significantly enhance research opportunity in atomic dynamics and push capability toward nuclear dynamics. DOI: 10.1103/PhysRevLett.110.104801