Ultrafast transmission electron microscopy: Principles and applications

In the realm of condensed matter physics, the properties of material are largely determined by the degrees of freedom associated with lattice, charge, orbital, and spin, as well as their intricate interplay. Unveiling the coupling mechanisms between these freedoms and effectively manipulating them necessitate a profound exploration into ultrafast dynamics, owing to the nanoseconds, femtoseconds, and even attoseconds timescales governing these fundamental interactions. Ultrafast transmission electron microscopy (UTEM) emerges as a powerful technique enabling the research of ultrafast dynamics with exceptional spatial-temporal resolution, showcasing diverse applications within nanoscale systems. Over the past decades, UTEM has witnessed significant advancements in instrument development, fostering its widespread utilization across various domains. This review firstly introduces the fundamental principles of UTEM and traces its historical evolution, intricately involving the integration of the pump-probe principle with transmission electron microscopy. Subsequently, the key performance characteristics of UTEM are succinctly summarized. Moreover, a detailed exposition is provided on the manifold applications of UTEM, encompassing structural dynamics, magnetic phenomena, and near-field optics, each delineated according to their respective time-resolved methodologies. Concluding the review, a forward-looking perspective on the UTEM technique is presented, envisioning its significance in the realm of ultrafast dynamics research.