Photo-induced Faraday rotation in GaAs/AlGaAs multiple quantum wells

The polarization rotation induced by the light pulse excitation is investigated on GaAs heterostructures. The temporal profile of the rotation angle shows an exponential decay reflecting the spin relaxation of excitons. The spectrally resolved transients exhibit not only the magnitude but the direction of the polarization rotation varies with the detection energy. The spectral features are in quantitative agreement with a calculation, where the saturation, the energy shift and the damping of the spin-polarized exciton resonance are taken into account.