Over the past few decades, X-ray free-electron lasers (XFELs) have become the pre-eminent tool for studying the structure and dynamics of materials at the molecular scale. Their bright, coherent, ultra-short X-ray pulses are ideal for imaging and manipulating dynamical molecular processes, which has been vital, for example, in the development of new pharmaceuticals and novel materials. A source of coherent gamma-ray pulses would enable analogous processes on the nuclear scale, with potential applications in imaging, security, energy storage, and fundamental science. Unfortunately, the current theoretical and computational tools essential for modelling XFELs cannot describe emission of gamma rays, where recoil effects play a significant role.

One practical limitation of XFELs is their physical scale: with undulators on the order of 100 m, and kilometre-long linear accelerators, there is scope for only a small number of such facilities worldwide, which limits their availability to users. The use of alternative undulator technologies with periods on the scale of microns rather than centimetres, would permit the use of lower energy electrons (100 MeV rather than 10s GeV), and hence greatly reduce the footprint of these facilities. As well as increasing availability of XFELs, this would also open the prospect of producing coherent gamma rays, since the lower energy electrons could take advantage of “quantum purification”, which prevents recoil effects degrading the beam quality and suppressing the FEL process.