THz electromagnetic wave radiation from DC-biased high-Q semiconductor microcavities

High-Q semiconductor microcavities (SMCs), where light-matter interactions can enter nonperturbative regime, provide a interesting system from both the viewpoints of fundamental physics and application. To date, the optical responses of such systems in frequency or time domain have been investigated intensively, and the basic characteristics such as the appearance of the polariton doublets and the corresponding normal mode oscillation (NMO) have been observed. However, the experiments done so far mostly dealt with the photonic part of the polaritons, and there has been a limited number of experiments proving the coherent dynamics of the excitons directly. Recently, it has been pointed out that the oscillation observed in four wave mixing (FWM) signals does not correspond directly to the NMO, because of the interference effect. Hence, to detect the NMO as an oscillation in the exciton population, a basic coherent exciton dynamics in a strongly coupled exciton-photon system, a more direct method is required. We present our experimental results on the detection of THz electromagnetic waves (EMWs) radiated from a DC-biased high-Q SMC. Since the EMWs are radiated, through optical rectification from the polarized excitons whose population oscillates as a result of the NMO, the observation of the EMW can be a more direct manifestation of the NMO and, in turn, of the coherent energy exchange between the excitons and photons.