Exploring Fast and Ultrafast Dynamics of Matter with Electrons and Photons

Opportunities in nanoscale probing of laser-driven phase transitions:<br/> <br/>For several decades, optical near-field microscopy facilitated pioneering investigations of photonic excitations at the nanoscale. In recent years, the near-field microscopy of terahertz fields has emerged as an important tool for experiments involving phononic and electronic phenomena, rich spatio-temporal dynamics, and highly nonlinear processes. Building on this foundation, this Perspective illuminates the transformative opportunities provided by terahertz near-field microscopy to probe ultrafast phase transitions, helping to tackle previously inaccessible challenges of condensed matter physics. In many systems, laser-driven phase transitions are accompanied by the generation of terahertz pulses with spatio-temporal features governed by the complex physics underlying the phase transition. Thus, characterization of the emitted pulses using terahertz near-field microscopy techniques could support the investigation of ultrafast phase transition dynamics. This approach could, for example, allow the observation of ultrafast topological transitions in quantum materials, showcasing its ability to elucidate the dynamic processes underlying phase changes.