Microcavity systems with organic luminescent materials have a hot prospect for room-temperature cavity-polariton devices. The polariton dispersion relation of organic microcavities is significantly different from that of inorganic microcavities due to the strong localization of Frenkel excitons. Also photoexcited particles will undergo a different cooling mechanism until they reach the polariton ground state. In the characterization of efficient polariton condensates, therefore, the polariton cooling dynamics as well as the kinetics of the polariton eigenstate should be measured. Here we present experimental studies on ultrafast dynamics of cavity polaritons in an organic singlecrystal microcavity under nonresonant pumping. In time-resolved photoluminescence measurements we observed, for the first time, an ultrafast dynamics of stimulated cooling of the organic cavity polariton. Transient transmission measurement enabled us to investigate the detailed renormalization dynamics of the polariton eigenstate. The results clearly demonstrated the prospect of organic microcavities for room-temperature polaritonic devices.

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Investigation of physics on light-matter interaction and strong coupling formation in organic microcavities is important to characterize the device structure enabling efficient room-temperature polariton condensation. In this study, we evaluate quantitatively the light-matter interaction parameters for three types of organic single-crystal microcavities and discuss the effects of microcavity structures on the strong coupling formation. We found that improvement in cavity quality factor causes a reduction in the photon damping constant, which results in an increase in the Rabi splitting energy. Moreover, when we used a metal thin film as the cavity mirror, it was revealed that the exciton damping became 30 times stronger than that in a dielectric mirror cavity. These experimental findings are very intriguing to achieve low-threshold or electrically pumped organic polariton devices.

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