中央研究院 原子與分子科學研究所

We show that a high-energy electron bunch can be used to capture the instantaneous longitudinal and
transverse field structures of the highly transient, microscopic, laser-excited relativistic wake with
femtosecond resolution. The spatiotemporal evolution of wakefields in a plasma density up ramp is
measured and the reversal of the plasma wake, where the wake wavelength at a particular point in space
increases until the wake disappears completely only to reappear at a later time but propagating in the
opposite direction, is observed for the first time by using this new technique.