Effect of pump-probe detuning on the Faraday rotation and ellipticity signals of mode-locked spins in InGaAs quantum dots

摘要

We have studied the Faraday rotation and ellipticity signals in ensembles ofsingly-charged (In,Ga)As/GaAs quantum dots by pump-probe spectroscopy. Fordegenerate pump and probe we observe that the Faraday rotation signal amplitudefirst grows with increasing the time separation between pump and probe before adecay is observed for large temporal separations. The temporal behavior of theellipticity signal, on the other hand, is regular: its amplitude decays withthe separation. By contrast, for detuned pump and probe the Faraday rotationand ellipticty signals both exhibit similar and conventional behavior. Theexperimental results are well described in the frame of a recently developedmicroscopic theory [Phys. Rev. B 80, 104436 (2009)]. The comparison betweencalculations and experimental data allows us to provide insight into thespectral dependence of the electron spin precession frequencies and extract theelectron g-factor dependence on energy.