Faraday-rotation spectrum of electron spins in microcavity-embedded GaAs quantum wells

Using the time-resolved magneto-optical Faraday effect, the dynamics of electron spins is measured in a GaAs quantum well embedded in a vertical one-dimensional optical cavity. The cavity leads to an enhancement of the Faraday-rotation amplitude that varies with the detuning between the QW absorption peak and the cavity resonance. We find a transition in the Faraday rotation spectrum that is triggered by the cavity detuning. This is attributed to a modification of the phase of the cavity reflectivity at the impedance-matching condition of the cavity. If the QW absorption is too small to compensate the asymmetry of the cavity mirrors, the Faraday-rotation signal is dominated by spin-induced circular birefringence, whereas contributions from circular dichroism predominate for higher quantum-well absorption. A numerical calculation of the Faraday-rotation spectrum is in good agreement with the experimental results. © 2005 The American Physical Society.