Opportunities in nanoscale probing of laser-driven phase transitions

For several decades, optical near-field microscopy has facilitated pioneering investigations of photonic excitations at the nanoscale. In recent years, near-field microscopy of terahertz fields has emerged as an important tool for experiments involving phononic and electronic phenomena, rich spatiotemporal dynamics and highly nonlinear processes. Building on this foundation, this Perspective elucidates the transformative opportunities provided by terahertz near-field microscopy to probe ultrafast phase transitions, helping to tackle previously inaccessible challenges of condensed matter physics. Laser-driven phase transitions in many systems are accompanied by the generation of terahertz pulses with spatiotemporal features governed by the complex physics underlying the phase transition. The characterization of these emitted pulses using terahertz near-field microscopy techniques could therefore 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 clarify the dynamic processes underlying phase changes. Optical near-field microscopy has facilitated our understanding of nanophotonics. This Perspective explores the opportunities that near-field studies of terahertz fields provide for ultrafast phase transitions in condensed matter systems.