We present the promise of generating gigawatt mode-locked multichromatic x rays in a seeded free-electron laser (FEL). We show that, by using a laser to imprint periodic modulation in electron beam phase space, a single-frequency coherent seed can be amplified and further translated to a mode-locked multichromatic output in an FEL. With this configuration the FEL output consists of a train of mode-locked ultrashort pulses which span a wide frequency gap with a series of equally spaced sharp lines. These gigawatt multichromatic x rays may potentially allow one to explore the structure and dynamics of a large number of atomic states simultaneously. The feasibility of generating mode-locked x rays ranging from carbon K edge (∼284eV) to copper L 3 edge (∼931eV) is confirmed with numerical simulation using the realistic parameters of the linac coherent light source (LCLS) and LCLS-II. We anticipate that the mode-locked multichromatic x rays in FELs may open up new opportunities in x-ray spectroscopy (i.e. resonant inelastic x-ray scattering, time-resolved scattering and spectroscopy, etc.). © 2012 American Physical Society.
Xiang, D., Ding, Y., Raubenheimer, T., & Wu, J. (2012). Mode-locked multichromatic x rays in a seeded free-electron laser for single-shot x-ray spectroscopy. Physical Review Special Topics - Accelerators and Beams, 15(5). https://doi.org/10.1103/PhysRevSTAB.15.050707