Nanoimaging and Nanospectroscopy of Polaritons with Time Resolved s-SNOM

The development of electronics and photonics is entering a new era of ultrahigh speed sensing, data processing, and telecommunication. The carrier frequencies of the next-generation electronic devices inevitably extend beyond radio frequencies, marching toward the nominally photonics-dominated territories, e.g., terahertz and beyond. As a result, electronic and photonic techniques naturally merge and seek common ground. At the forefront of this technical trend is the field of polaritonics, where polaritons are half-light, half-matter quasiparticles that carry the properties of both "bare" photons and "bare" dipole-carrying excitations. The Janus-faced nature of polaritons renders the unique capability of operando control using photoexcitation or applied electric field. Here, state-of-the-art ultrafast polaritonic phenomena probed by scattering-type scanning near-field optical microscope (s-SNOM) techniques is reviewed. The ultrafast dynamical control and loss-reduction of the polariton propagation are discussed with special emphasis on the creation and probing of the tip or edge induced plasmon- and phonon-polaritons in low-dimensional systems. The detailed technical aspects of s-SNOM and its possible future development are also presented.