Floquet-Bloch shifts in two-band semiconductors interacting with light

We consider harmonic generation from a semiconductor described in the two-band approximation. In particular, the signatures of the Floquet-Bloch states in the low-order harmonic spectra are studied. We find field-strength-dependent shifts of the position of resonant peaks. The shifts are analogous to the ponderomotive shifts in strong-field physics of atoms and molecules. We illustrate this theory by analyzing low-order harmonics generated from hexagonal boron nitride.