Polariton-based devices require materials where light-matter coupling under ambient conditions exceeds losses, but our current selection of such materials is limited. Here we measured the dispersion of polaritons formed by the A and B excitons in thin MoS2 slabs by imaging their optical near fields. We combined fully tunable laser excitation in the visible with a scattering near-field optical microscope to excite polaritons and image their optical near fields. We obtained the properties of bulk MoS2 from fits to the slab dispersion. The in-plane excitons are in the strong regime of light-matter coupling with a coupling strength (40−100meV) that exceeds their losses by at least a factor of two. The coupling becomes comparable to the exciton binding energy, which is known as very strong coupling. MoS2 and other transition metal dichalcogenides are excellent materials for future polariton devices.
