We demonstrate that the optical orientation of excitons can be coherently controlled and directly observed in a resonant time resolved photoluminescence experiment. The optical dephasing time of excitons, their longitudinal and transverse spin relaxation times, and their radiative lifetime, are measured with strictly the same experimental conditions. The measurements rely on the linear response of the crystal.

• Received 5 June 1997

DOI:https://doi.org/10.1103/PhysRevLett.79.3222