Doubly resonant terahertz sideband generation in quantum wells: Optical signatures of terahertz-dressed subbands

The propagation of light through quantum wells in the vicinity of a pair of excitonic resonances dressed by a far-infrared (THz) electric field is considered. The THz frequency is tuned near resonance with (half) the splitting between the exciton levels (for an inversion symmetric system). It is found that even if excitation from the crystal ground state to one of the pair of levels is optically forbidden, it may nevertheless have a strong influence on the optical spectra due to the THz-induced hybridization of the levels (Autler-Townes splitting). If the optical transition from the crystal ground state to each of the two levels is allowed, the optical spectra of the pair of dressed levels exhibit multiple peaks.