Four-wave mixing and terahertz emission from three-level systems in quantum wells: effects of inhomogeneous broadening

摘要

Using a perturbation theory based on the density-matrix formulation, we studythe nonlinear optical responses of a noninteracting three-level model system toconsecutive coherent pulsed excitations, as realized in several recentexperiments involving excitonic transitions in quantum wells. The terahertzemission, which is a second order response, and the four-wave mixing signal, athird order response, are calculated within the rotating-wave approximation, inthe presence of detuning, dephasing, and inhomogeneous broadening. We study thequantum beats in the photon echo from transient four-wave mixing experiments ofa three-level system. We find that the temporal profile of the photon echosignal in the four-wave mixing experiments depends very strongly on the amountof inhomogeneous broadening of the energy levels involed. Both the position andthe intensity of the peaks exhibit a smooth evolution from strong quantum beatsto a conventional photon echo as the inhomogeneous broadening increases. Thesefeatures from our noninteracting model system are compared with a recentexperiment, and found to account for a number of experimental observations.