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

TL;DR

This paper models the nonlinear optical responses, including terahertz emission and four-wave mixing, of three-level quantum well systems, highlighting how inhomogeneous broadening influences photon echo signals and quantum beats.

Contribution

It provides a theoretical analysis of nonlinear optical effects in three-level quantum well systems, incorporating inhomogeneous broadening effects to explain experimental observations.

Findings

Photon echo profiles depend strongly on inhomogeneous broadening.

Quantum beats evolve smoothly into conventional photon echoes with increasing broadening.

The model explains several experimental results in quantum well systems.

Abstract

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