An analytical investigation of excitonic absorption in terahertz-driven quantum wells

Abstract

An analytical solution of the optical susceptibility of quantum wells driven by a terahertz (THz) field is achieved based on the density-matrix formalism. A simplified three-level model is adopted for the quantum well structures, with the levels coupled by a near-infrared (NIR) and a THz field. The equation of motion for the polarization is derived from Liouville's equation for the density matrix. Using Floquet's theorem, and under the rotating-wave approximation with respect to the NIR probe field, analytical expression for the optical susceptibility of the driven quantum wells is obtained. Different features rising induced by the driving THz field in the absorption spectrum of the NIR probe are discussed for the THz field near resonance and out of resonance of the intraexcitonic transition. This analytical investigation of the susceptibility of the THz-field-driven quantum wells is much useful for clearly identifying the physical principles obscured in the full numerical calculations.