Terahertz Microscopy Down to the Atomic Scale

In this talk I will review terahertz scanning probe microscopy with a focus on recent developments that have made experiments with simultaneous ultrafast temporal resolution and atomic spatial resolution possible. Specifically, I will discuss the underlying principle of coupling terahertz radiation to sharp metallic tips, the connection between scattering-type scanning near-field optical microscopy (SNOM) and terahertz lightwave-driven scanning tunneling microscopy (THz-STM), and the key aspects of THz-STM that enable atomic spatial resolution. Finally, as an illustrative example, I will present ultrafast THz-STM snapshots and pump-probe measurements of electron densities in selected molecular orbitals of single molecules with sub-Angstrom spatial resolution [1].