[Perspective] Electrons catch a terahertz wave

Electron microscopy and diffraction are incredibly successful techniques for studying the structure of matter on the atomic scale. Making these techniques “ultrafast”—that is, using pulses of femtosecond duration—could provides us with unprecedented microscopic vistas into how materials evolve on time scales typical of atomic motions (1, 2). One of the key challenges in this research area is the controlled generation of short flashes of electrons. On page 429 of this issue, Kealhofer et