High-resolution correlative imaging in ultrafast electron microscopy

Ultrafast electron microscopy (UEM) has a broad scope of application across material systems and scientific disciplines. In UEM, we investigate multiscale dynamics in the spatial domain ranging from micrometres to angstroms, in reciprocal space, and on timescales from microseconds to attoseconds, with an energy resolution of a few electronvolts or less. Notably, UEM has played a pivotal role in visualisation of ultrafast structural dynamics with high local selectivity, enabling the exploration of the dynamic nature of chemical bonding in non-equilibrium states and investigation of electron - photon interactions to manipulate free-electron wavefunctions. This breakthrough has created new opportunities in condensed matter physics, chemical dynamics, and quantum electrodynamics. In addition, efforts are underway to achieve high-resolution UEM in correlative real-space microscopy to diffractography and spectroscopy in a single instrument for comprehensive investigations of light - matter interactions and structure - dynamics - function relations. In this review, we provide an overview of the current state of UEM imaging capabilities and scientific interests, outlining the technological challenges faced by UEM in related fields and exploring potential approaches to overcome these challenges. Furthermore, we highlight the emerging fields of interest and present future perspectives that can further extend the imaging capabilities of UEM.