Coherence of femtosecond single electrons exceeds biomolecular dimensions

Time-resolved diffraction and microscopy with femtosecond electron pulses provide four-dimensional recordings of atomic motion in space and time. However, the limited coherence of electron pulses, reported in the range of 2–3 nm, has so far prevented the study of complex organic molecules with relevance to chemistry and biology. Here we characterize the coherence of femtosecond single-electron pulses that are generated by laser photoemission. We show how the absence of space charge and the minimization of the source size allow the transverse coherence to be extended to 20 nm at the sample position while maintaining a useful beam diameter. The extraordinary coherence is experimentally demonstrated by recording single-electron diffraction snapshots from a complex organic molecular crystal and identifying more than 80 sharp Bragg reflections. Further optimization affords promise for coherences of 100 nm. These advances will allow time-resolved imaging of functional dynamics in biological systems, uniting picometre and femtosecond resolutions in a compact, table-top instrumentation.