It is demonstrated that during the first few picoseconds after resonant femtosecond excitation the secondary radiation from a strongly coupled semiconductor microcavity containing one quantum well is dominated by Rayleigh scattered light. At early times after excitation (<10 ps) the two polariton modes emit with almost equal intensity resulting in a strong beating of the emission. For longer times (>10 ps) the lower polariton branch provides the most intense emission which is due to incoherent luminescence. The results in the Ray leigh scattering regime are shown to be in excellent agreement with a theoretical model of coherence transfer due to interface roughness. [S0163-1829(98)52940-2].