Comparative analysis in the frequency domain of the resonant interaction between an ultrashort pulse train and a two-level system

We investigate the problem of two-level atoms driven by an ultrashort pulse train in the frequency domain. At low intensity regime, we obtain a perturbative analytical solution that allows us to discuss the role of the mode number of the frequency comb near or at resonance in the temporal evolution of the atomic coherence. At high intensities, the effect of the number of modes is analyzed on the steady-state regime through numerical calculations.