THz spectroscopy of semiconducting plasmonic resonators

We investigate the photo-excitation of localized surface plasmon polaritons (LSPPs) in semiconductor structures at THz frequencies by the optical pumping of electrons across the semiconductor energy bandgap. This excitation can be actuated in picosecond time scales, enabling ultrafast THz plasmonics. The concept of active plasmonics can be extended to a full spatial and temporal optical control of plasmonic resonances using the structured illumination of flat semiconductors. This control has lead to the observation of strong capacitive coupling and charge transfer plasmons in dimers with very small gaps. Furthermore, we show that LSPPs can enhance THz local fields in subwavelength volumes by several orders of magnitude. This field enhancement is used to probe very thin organic layers.