Summary form only given. The dynamics of polaritons in microcavity samples is presently under intense debate, in particular whether or not the so-called Boser action is possible. In this work, we investigate a /spl lambda/ cavity with a homogeneously broadened 25 nm GaAs quantum well at the antinode at a temperature of 10 K. We can thus inject well-defined polariton populations in k-space revealing how different initial and final state populations may influence the dynamics.