Off-Resonance Time-Resolved Kerr Rotation Spectroscopy

We show that time-resolved Kerr rotation (TRKR) is a quantitatively accurate tool to measure spin dynamics, even when conducted highly off resonance. We find that TRKR measurements have essentially identical temporal profiles when the probe energy is tuned far below, far above, and on resonance with a semiconducting band gap. We also present energy dependent TRKR spectra, and show they have an odd Lorenztian profile around the semiconducting band gap, at odds with the simplest theoretical model which predicts an even Lorenztian form. We show that this discrepancy is resolved if one accounts for a decrease in the transition linewidth as the optical energy increases above the band-edge transition.