Spatially Structured Carrier Density in Photoexcited Van der Waals Semiconductors

ABSTRACT Photoexcitation of non‐equilibrium carriers in semiconductors provides a promising route for ultrafast nanophotonic control. While temporal modulation of carrier excitation has been widely explored, spatially reconfigurable photocarrier distributions offer an additional degree of freedom for manipulating light–matter interactions at the nanoscale. Here, we demonstrate an all‐optical approach that engineers the interference field formed by the superposition of incident pump light and edge‐scattered surface waves near the apex of a scanning tip, thereby imprinting spatially structured carrier patterns in van der Waals semiconductors. Ultrafast infrared near‐field microscopy serves as a sensitive proxy for these patterns in tin selenide nanosheets, revealing periodically modulated infrared signals with up to twenty‐fold wavelength compression relative to the incident light. Fourier and time‐resolved analyses show that the fringe periodicity is governed by the optically imprinted carrier modulation rather than by propagating plasmons, while finite‐dipole modeling quantifies the carrier dynamics. This work establishes a general framework for all‐optical, subwavelength control of infrared responses through near‐field interference, offering new opportunities for reconfigurable nanophotonic and plasmonic functionalities in low‐dimensional semiconductors.