First-order coherent THz optical sideband generation from asymmetric QW intersubband transitions

We have generated terahertz (THz) optical sidebands on a near-infrared probe beam by driving an excitonic intersubband resonance with THz electric fields. We use THz radiation polarized along the non-centro-symmetric axis of a quantum well system to generate a comb of sidebands ωsideband=ωNIR+nωTHz. In exploring the rich polarization of the processʹs power, and NIR frequency dependences we encounter both an efficient perturbative regime modeled by a X(2) non-linear susceptibility, and a non-perturbative regime which has not been previously explored in driven quantum systems.