Annular resonant Rayleigh scattering in the picosecond dynamics of cavity polaritons

We study the angular dependence of the emission from cavity polaritons resonantly excited by a picosecond laser pulse. We observe that, in a first stage, the initial excitation is rapidly redistributed by elastic scattering along a well-defined ring in the wave-vector space which results in an angular-dependent emission. This initial transfer, which conserves the polarization, is attributed mainly to resonant Rayleigh scattering of polaritons. We also study the width of this ring and show that it is detuning dependent, reflecting the energy dispersion of the polaritons. At longer delay, the emission is found to be isotropic and depolarized, in agreement with previous studies.