Resonantly enhanced reflection of quadrupole polaritons in Cu2O

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