Photoemission Electron Microscopy of Exciton–Polaritons in Thin WSe₂ Waveguides

Exciton–polaritons emerging from the interaction of photons and excitons in the strong coupling regime are intriguing quasiparticles for the potential exchange of energy during light–matter interaction processes, such as light harvesting. The coupling causes an energy anticrossing in the photon dispersion centered around the exciton resonance, i.e., a Rabi splitting between a lower and upper energetic branch. The size of this splitting correlates with the coupling strength between the exciton and photonic modes. In this work, we investigate this coupling between excitons and photonic waveguide modes excited simultaneously in thin-film flakes of the transition-metal dichalcogenide WSe2. Using a photoemission electron microscope, we are able to extract the dispersion of the transverse electric and magnetic modes propagating through these flakes as well as extract the energy splitting. Ultimately, our findings provide a basis for the investigation of the propagation of exciton–polaritons in the time-domain via time-resolved photoemission.