Numerical Study of Carrier Dynamics in Pump-Probe Near-Field Nanoscopy

The continuing miniaturization of semiconductor devices necessitates advanced techniques to probe carrier distribution and dynamics with high resolutions on both length and time scales. Pump-probe scattering-type scanning near-field optical microscopy (s-SNOM) combines the advantages of tip-based high spatial resolution and ultrafast optics to enable the measurement of carrier dynamics on the nanoscale. However, the interpretation of pump-probe s-SNOM usually relies on analytical models that necessarily carry simplifications. Here, we numerically model pump-probe s-SNOM with a finite-difference time-domain (FDTD) approach. By simulating the nanoscale tip-sample interactions, we reveal the transient near-field responses of silicon nanowires and resolve their carrier dynamics from experimental pump-probe s-SNOM results. Our work provides a validated framework for ultrafast near-field characterization of thermodynamic phenomena in a broad range of functional materials to advance the design of next-generation semiconductor devices.