  In this article, we illustrate how the Coulomb field of a highly relativistic
electron beam can be shaped into a broadband pulse suitable for driving
ultrafast and strong-field physics. In contrast to a solid-state laser, the
Coulomb field creates a pulse which can be intrinsically synchronized with an
x-ray free electron laser (XFEL), can have a cutoff frequency which is broadly
tunable from THz to EUV, and which acts on target systems as a "half-cycle"
impulse. Explicit examples are presented to emphasize how the unique features
of this excitation can be a tool for novel science at XFEL facilities like the
LCLS.
