Direct observation of picosecond spin relaxation of excitons in GaAs/AlGaAs quantum wells using spin-dependent optical nonlinearity

We have directly observed spin relaxation of excitons in the picosecond region using time-resolved polarization absorption measurements. With the help of spin-dependent optical nonlinearity of excitonic absorption, we obtained a fast decay of spin-up carriers and a fast accumulation of spin-down carriers with a spin relaxation time of 32 ps for a GaAs/Al0.51Ga0.49As multiple quantum well at room temperature with a time resolution of 1 ps.