Anomalous Fresnel Coefficients for Orthoexciton–polaritons in Cu2O

Using resonant two-photon excitation, we create a coherently propagating orthoexciton–polariton wave packet and measure its reflectance (R) and transmittance (T) at the boundary opposite the incoming surface. We find an enhanced reflection of orthoexciton–polaritons from sample surfaces such that the ratio T/R deviates significantly from the present theory based on the additional boundary condition. This anomalous boundary effect most likely arises from the quadrupole excitonic component of orthoexciton–polaritons, resulting in an enhanced reflection at boundaries.