Figure 9.

Illustration of XLEAP operation

The electron beam forms a single-cycle energy modulation by itself in a long-period wiggler. Then, the energy modulation is transferred into a single density spike for generating attosecond X-ray pulses. This setup is naturally compatible with high repetition rate XFELs, as it is based solely on a passive wiggler. Reprinted with permission from.¹²⁵ Reprinted with permission from the Copyright Clearance Center: Springer Nature, Nature Photonics, (Duris et al.,¹²⁵ Tunable isolated attosecond X-ray pulses with gigawatt peak power from a free-electron laser), Copyright (2020).