Abstract
Time-resolved electron microscopy is based on the excitation of a sample by pulsed laser radiation and its probing by synchronized photoelectron bunches in the electron microscope column. With femtosecond lasers, if probing pulses with a small number of electrons—in the limit, single-electron wave packets—are used, the stroboscopic regime enables ultrahigh spatiotemporal resolution to be obtained, which is not restricted by the Coulomb repulsion of electrons. This review article presents the current state of the ultrafast electron microscopy (UEM) method for detecting the structural dynamics of matter in the time range from picoseconds to attoseconds. Moreover, in the imaging mode, the spatial resolution lies, at best, in the subnanometer range, which limits the range of observation of structural changes in the sample. The ultrafast electron diffraction (UED), which created the methodological basis for the development of UEM, has opened the possibility of creating molecular movies that show the behavior of the investigated quantum system in the space-time continuum with details of sub-Å spatial resolution. Therefore, this review on the development of UEM begins with a description of the main achievements of UED, which formed the basis for the creation and further development of the UEM method. A number of recent experiments are presented to illustrate the potential of the UEM method.
Highlights
The structural dynamics of matter induced by powerful pulsed laser radiation manifests itself in an atomic–molecular movie, the study of which is of great interest to modern science
At the beginning of the 21st century, scientists at the California Institute of Technology reported about the first series of experiments that were conducted on a transmission electron microscope modified to directly observe the structural dynamics of matter on a picosecond time scale, which was extended to the femtosecond range, which marked the birth of ultrafast electron microscopy (UEM)
The ultrafast electron diffraction (UED), which created the methodological basis for the development of UEM, has opened the possibility of creating molecular movies that show the behavior of the investigated quantum system in the space-time continuum with details of sub-Å spatial resolution
Summary
The structural dynamics of matter induced by powerful pulsed laser radiation manifests itself in an atomic–molecular movie, the study of which is of great interest to modern science. To this end, it is necessary to ensure a high spatiotemporal resolution, which implies the development of special research methods. At the beginning of the 21st century, scientists at the California Institute of Technology reported about the first series of experiments that were conducted on a transmission electron microscope modified to directly observe the structural dynamics of matter on a picosecond time scale, which was extended to the femtosecond range, which marked the birth of ultrafast electron microscopy (UEM). In contrast to a fairly recent review [11], we confine ourselves to the stroboscopic mode of operation of the time-resolved electron microscope, when it becomes possible to experimentally detect fast processes on pico-femto-attosecond scales
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