When we want to examine ultrafast, irreversible microscopic dynamics by electron microscopy, we are faced with instrumental limitations. Stroboscopic techniques, with repetitive system excitation and image formation, work well for reversible systems. Alternatively, using specialty scanning electronics and deflectors, one can examine a pulsed image in a manner similar to a streak camera. While suited to irreversible dynamics, the latter method seems to be limited to the nanosecond regime and slower.
Basklin, Liu and Zewail of Caltech have recently introduced a multi-cathode technique which promises to give picosecond regime imaging of irreversible phenomena. Their electron bunches are generated by multiple, spatially separated photocathodes, each triggered by one and the same UV pulse. Because of the cathode spatial separation, the respective electron images are also spatially separated at the detector. Because of the temporal separation, each electron image samples the dynamic process at a different point in time. Their experimental proof of principle shows 19 ps delay between two beams impinging on a photo-excited gold sample.
Reference: PNAS 111(2014)10479-84 (open access)