Subpicosecond pump-and-probe study on exciton-polaritons in semiconductor-embedded photonic crystal slab

We report the photo-induced transmission change of the photonic crystal slab in which an active semiconductor, (C6H5C2H4NH3)2PbI4, is introduced. In the transmission spectrum without irradiating the pump light, sharp dips are observed, which are attributed to the excitation of exciton-polaritons (mixed modes of excitons in the embedded semiconductor and quasi-guided optical modes) in the slab. It is found that, by pumping below the exciton resonance, the dips blue-shift transiently during the irradiation of the pump light (200 fs). By pumping at the exciton resonance, the dips blue-shift and are bleached with a decay time of about 10 ps. These phenomena are explained on the basis of the excitonic nonlinearity.