Fig. 3
Quantitative interpretation of the experiment via the 3rd order nonlinear polarization model. Comparison of the 3rd order nonlinear polarization model describing phonon driven optical band gap modulation (red solid curve) with the experimental data (black circles) in the frequency domain at the probe frequency of a 1.61 and b 1.62 eV, respectively. Resonant excitation of 1 THz mode describes the oscillatory behavior very well, whereas the other possibility, non-resonant excitation of 1.9 THz mode shows a 90° phase shift (blue dashed curve) for both energies. Inset: Same comparison in the time domain. See SI for detailed explanation of the modeling
