Ultrafast Light and Electrons: Imaging the Invisible

In this chapter, the evolutionary and revolutionary developments of microscopic imaging are overviewed with focus on ultrashort light and electrons pulses; for simplicity, we shall use the term “ultrafast” for both. From Alhazen’s camera obscura, to Hooke and van Leeuwenhoek’s optical micrography, and on to three- and four-dimensional (4D) electron microscopy, the developments over a millennium have transformed humans’ scope of visualization. The changes in the length and time scales involved are unimaginable, beginning with the visible shadows of candles at the centimeter and second scales, and ending with invisible atoms with space and time dimensions of sub-nanometer and femtosecond, respectively. With these advances it has become possible to determine the structures of matter and to observe their elementary dynamics as they fold and unfold in real time, providing the means for visualizing materials behavior and biological function, with the aim of understanding emergent phenomena in complex systems. Both light and light-generated electrons are now at the forefront of femtosecond and attosecond science and technology, and the scope of applications has reached beyond the nuclear motion as electron dynamics become accessible