Light-Induced In Situ Transmission Electron Microscopy—Development, Challenges, and Perspectives

[Image: see text] Transmission electron microscopy is a basic technique used for examining matter at the highest magnification scale available. One of its most challenging branches is in situ microscopy, in which dynamic processes are observed in real time. Among the various stimuli, like strain, temperature, and magnetic or electric fields, the light–matter interaction is rarely observed. However, in recent years, a significant increase in the interest in this technique has been observed. Therefore, I present a summary and critical review of all the in situ experiments performed with light, various technical possibilities for bringing radiation inside the transmission electron microscope, and the most important differences between the effects of light and electrons on the studied matter. Finally, I summarize the most promising directions for further research using light excitation.