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Ultrafast vibrational and electronic spectroscopy unravels the dynamics underlying the functionality of quantum, energy, and biological materials. To understand and ultimately control the processes that underly the emergent function in these materials requires imaging the elementary excitations on their natural time and length scales. To achieve this goal, we have developed scanning probe microscopy with ultrafast and shaped laser pulse excitation for multiscale spatio-temporal optical nano-imaging. However, mostly limited to short-lived transient states, the contrast obtained has remained insufficient to probe important weak and long-lived excitations such as low-conductivity carriers, molecular vibrations, lattice phonons, and their couplings. Here, we demonstrate ultrafast heterodyne pump-probe (HPP) nano-imaging to simultaneously resolve quantum dynamics in space, time, and frequency. In ultrafast infrared nano-imaging based on excitation modulation and sideband detection we isolate and selectively characterize excited-state electron and vibration dynamics from femto- do micro-second times scales. In exemplary applications I will show ultrafast movies to resolve the fundamental quantum dynamics from the few-femtosecond coherent to the thermal transport regime. Specifically, in quantum materials, in ultrafast nano-imaging of photoinduced carrier and phase behavior we identify distinct transient nano-domain behavior revealing competing electronic and lattice degrees of freedom. Further in lead halide perovskites from transient vibrational nano-FTIR imaging we resolve excited state polaron dynamics and polaron-cation coupling underlying their photovoltaic response. Lastly, by simultaneous probing of carrier dynamics and interfacial phonon softening we establish nano-thermometry to imagine interfacial thermal transport dynamics in 2D semiconductor/insulator heterostructures. These examples show how HPP nano-imaging opens the door to elementary processes and interactions in functional materials with full spatio-temporal-spectral resolution.
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