With advances in spatial resolution reaching the atomic scale, 2- and 3-dimensional
(D) imaging in transmission electron microscopy (TEM) has become an essential
methodology in various fields of research providing structural information. Recently,
at Caltech it has become possible to successfully integrate the ultrahigh temporal
resolution (4th dimension) to the three dimensional spatial resolution of TEM. Here,
presented is the concept of time-resolved imaging in 4-D ultrafast electron
microscopy (UEM) for the study of structural dynamics. The potential for the
applications of UEM is elucidated with three examples, i.e., structural and
morphological dynamics of gold, mechanical vibration of graphite, and phase
transition of silicon, which are initiated by laser-induced heat impulses and take
place on distinctive time scales.