The importance of disorder in very high quality semiconductor microcavities

We investigate a semiconductor microcavity containing a quantum well, a sam ple of exceptional quality. We observe a four-wave mixing response which re sembles that of an inhomogeneously broadened exciton system, while the line ar transmission measurements are affected by the homogeneous part of the br oadening and have a completely different decay time. We show that the four- wave mixing response cannot be calculated using the excitonic parameters (l inewidth and relaxation time) extracted from the linear transmission measur ements, as the coupling of exciton and photon states deeply modifies the sc attering channels.