Time-resolved THz-TDS Nanoscopy for Probing Carrier Dynamics with Femtosecond Temporal and Nanometer Spatial Resolution

By combining THz-TDS based scattering near-field optical microscopy (THz s-SNOM) with VIS/NIR ultrafast pump-probe spectroscopy we enable probing of dynamic material properties with femtosecond temporal and 20nm spatial resolution. We demonstrate s-SNOM based ultra-fast pump-probe THz-TDS imaging and spectroscopy as well as time-resolved THz near-field transient measurements at extreme sub-wavelength scale sample structures. As a representative material system, we study the spatial heterogeneity of photoexcited carriers in a silicon based semiconductor device and a micron-sized MoS₂ crystal. For the latter, near-field THz transients reveal thickness/layer dependent decay dynamics and lifetimes in the picosecond range.