The Science

To build everything from better electronics to cleaner energy, researchers need to know the details. To do that, scientists produced multiple pulses of ultra-short X-rays. The X-rays can reveal ultrafast physical and chemical changes in reactions. The Fresh-slice improves the performance over the existing scheme in terms of pulse intensity and customizability, in a simple setup. For the first time, up to three intense pulses are available with the Fresh-slice scheme allowing the excitation of the sample with a pair of X-ray pulses and probing it with the third one.

The Impact

X-ray beams are beneficial in determining how molecules and materials behave. The resulting data is needed for new materials for electronics and cleaner energy. The Fresh-slice scheme produces highly customizable X-ray pulses with unprecedented performance, offering new insights into ultrafast changes. This research paves the road for creating completely new scientific instrument concepts and improving the performance on existing instruments.


A “dechirper” system designed by SLAC and RadiaBeam has been recently installed at the Linac Coherent Light Source to control the electron bunch energy profile, and therefore the X-ray spectrum. In addition to the chirp control, SLAC scientists found another innovative application for the device. When the electron bunch travels close to a corrugated metal wall in the dechirper, the bunch head keeps travelling straight, while the bunch-tail receives a strong deflection. Downstream of the device each temporal slice of the electron bunch follows a different trajectory. In the undulator line, strong permanent magnets wiggle the electrons that emit X-rays, but only a slice travelling straight on the undulator axis will be lasing efficiently. The lasing slice can be selected with beam orbit control along the undulator line, while other slices stay ”fresh” retaining full lasing capability in subsequent undulator sections. Because every pulse is produced by a different fresh electron bunch slice, free-electron lasers can reach saturation at each stage with high power. X-rays colors are controlled by the strength of the undulator field. Relative arrival time is controlled by the magnetic chicanes. Scientists have used the “Fresh-slice” scheme to produce up to three intense multi-color pulses. Future multi-stage amplification schemes could produce a pulse in an upstream undulator section, which is then amplified by a Fresh-slice in a downstream section.



The U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences, Scientific User Facilities Division funded the research, which uses resources at the Linac Coherent Light Source, DOE Office of Science scientific user facility.


A.A. Lutman, T.J. Maxwell, J.P. MacArthur, M.W. Guetg, N. Berrah, R.N. Coffee,  Y. Ding, Z. Huang, A. Marinelli, S. Moeller, and J.C.U. Zemella, “Fresh-slice multicolour X-ray free-electron lasers.” Nature Photonics 10, 745-750 (2016). [DOI: 10.1038/nphoton.2016.201]