3. In the case that the frequency of the pump field is on resonance with the equilibrium quasiparticle gap, the observed shift of energies resulting from hybridization of Floquet-bands are known as the ac-Stark effect. We discuss how this follows from Floqeut theory and explain the limits in which the well known formula for the shift as a function of energy holds. Among others, this gives a systematic explanation of the mechanism behind recently observerd optical Stark effects in TMDs\cite{sie_valley-selective_2014}.

Fig. 3. ”beyond ac-Stark” scaling and dependence of shift on pump parameters