Electrons catch light pulses on the fly

Although free electrons are widely used as probes to analyze the morphology, atomic structure, and optical properties of nanoscale materials using transmission or scanning electron microscopy, they can also interact strongly with light and, thus, sample the distribution of optical fields in and around those materials with high spatial resolution (1–3). Specifically, in photon-induced nearfield electron microscopy (PINEM), intense light fields bring an electron into multiple energy states simultaneously—a quantum-mechanical superposition state—which are then measured with an electron spectrometer. On page 168 of this issue, Yang et al. (4) report the use of PINEM to examine the creation of special light pulses known as solitons in an optical integrated circuit. The electron–soliton interaction shapes the electron’s probability distribution in space and time, thereby enabling new ways to probe ultrafast dynamics in matter with an electron microscope.