THz-electromagnetic wave radiation from semiconductor microcavities in strong- and weak-coupling regime

Light-matter interactions in semiconductor microcavities (SMCs) are drastically modified from those in free space. In particular, a single state of excitons would coherently couple with a single cavity mode, if the damping rates of the coherent excitations in their states are sufficiently low, resulting in the formation of exciton-photon coupled states called cavity-polariton modes. Such a strongly-coupled system provides an interesting system from both the viewpoints of fundamental physics and applications, and has been a subject recent intensive research. One of the unique phenomena in the cavity-polariton system is the nutation of exciton or photon populations called normal mode oscillation (NMO) triggered by short laser pulses. The NMO can be observed as the oscillation in the resonant light emissions, or in the pump-probe or four-wave mixing signals. In the present work, focusing on the SMCs under static electric field, we have investigated the NMO from another aspect, i.e, the THz-electromagnetic wave radiation. Since the excitons under static electric field are spatially polarized and carry static dipoles, the change in exciton population leads to the radiation of electromagnetic waves. We have already reported the first observation of THz-waves from cavity-polaritons. In the paper, we present the results of a more systematic experiment