ABSTRACT
The studies described in this chapter convince the reader that time-resolved polarimetry is an extremely sensitive way to study many body effects. The vectorial dynamics contain useful information about many-body effects, quantum interference and optical anisotropies that would be difficult to obtain in any other way. The chapter begins with a brief review of some of the four-wave-mixing (FWM) techniques that have been most commonly used to measure the coherent emission from multiple quantum wells (MQWs). The ellipticity and the fraction of unpolarised light are both significantly smaller for the negative delay. These features provide additional tests for any proposed model that purports to describe coherent excitonic dynamics in MQWs. The chapter discusses the treatment of excitons in semiconductors as two-level systems, and follows with a detailed review of the solutions to the density matrix equations for two independent two-level systems, with an emphasis on the vectorial nature of the FWM emission from such systems.
