Fig. 1
From: Coherent control in the extreme ultraviolet and attosecond regime by synchrotron radiation

Schematic layout of the experimental setup. Individual relativistic electrons traversing inside the twin undulators generate a pair of linearly-polarized electromagnetic wave packets. Each of the light wave packets has a duration of ~1.8 fs and consists of 10-cycle oscillations. Some 109 of light wave packet pairs with this common waveform, distributing randomly in time, constitute a light pulse (300-ps duration) from the twin undulators