Observation of population transfer to dark exciton states by using spin-diffracted four-wave mixing

We observed the exciton spin dynamical processes in GaAs quantum wells at low temperatures by three-pulse spin-diffracted four-wave mixing measurements. After investigating the merits and demerits of this method as compared with the pump–probe method, we discuss the excitation power dependence of exciton spin relaxation and the population transfer to the dark states.