The emission from a microcavity in the strong coupling regime excited resonantly by linearly polarized light has been measured with spatial, directional, and temporal resolution. We observe ballistic propagation of the excited polaritons as a ring spreading in real space. The linear polarization degree $P$ of the emission at the ring is found to oscillate as a function of the azimuthal angle $\theta$ and of time $t$ according to $P=\sin \left(2\theta \right)\sin ({\Omega }_{LT}t∕2)$, where ${\Omega }_{LT}$ is the longitudinal-transverse splitting of the exciton-polariton modes. This dependence holds for all investigated excitation energies corresponding to different values of ${\Omega }_{LT}$. The theoretical model assuming ballistic propagation of exciton polaritons in the specific cavity structure yields a detailed agreement with the experimental data. The observed polarization beats have the same nature as the recently predicted optical spin Hall effect.

• Received 8 November 2006

DOI:https://doi.org/10.1103/PhysRevB.75.075323