摘要： Quantum interactions between transition metal dichalcogenides (TMDs) and optical cavities are rapidly becoming an appealing research topic since these interactions underly a broad spectrum of optical phenomena. Here, we fabricate a simple device in which coherent strong coupling interactions occur between a photonic crystal (PhC) slab and monolayer tungsten disulfide (WS2). Both steady-state angle-resolved spectroscopy and transient absorption microscopy (TAM) are employed to explore the coupling behavior of this device. Specifically, anticrossing dispersions are observed in the hybrid device, indicating a Rabi splitting of 40.2 meV. A newly formed spectral feature emerges in the transient absorption (TA) spectrum of this polariton device under near-resonant excitation, which is subsequently evidenced to be a signature of the upper hybrid exciton–polariton state. Moreover, by carefully analyzing the ultrafast responses of both bare WS2 and the WS2-PhC polariton device excited both off resonance and near resonance, it is found that nonequilibrium thermal decay induces Coulombic screening in the monolayer WS2, which has a major impact on the formation of exciton–polariton. The results of this work could not only improve the current understanding of photophysics in the strong light–matter coupling regime but also lay the foundation for tailoring the development of TMD-based coherent devices.