Study on the coherent excitonic nonlinearity in semiconductor quantum wells by four-wave mixing spectroscopy

Hoang Ngoc Cam

Hoang Ngoc Cam

The paper presents a description of two-pair correlations in an electron-hole system in laser-excited direct-gap semiconductors in terms of the exciton-boson formalism. The dependence of the states of quasi-particles on their angular momentum orientation is properly taken into account following group theory rules. It is shown for the example of heavy hole excitons in GaAs quantum wells that Coulomb two-exciton correlations include effective repulsion between excitons with nonzero total momenta and effective attraction between excitons with zero total momenta. They generate exciton and biexciton nonlinearities, respectively, in the exciton-biexciton system. The Heisenberg equations of motion derived are applied to four-wave mixing in the coherent mode. Two components of Coulomb two-exciton correlations were found to generate coherent four-wave mixing either separately, one at the cocircular and the other at the perpendicular-linear polarization of applied pulses, or jointly at parallel-linear polarization. General equations are obtained for the amplitude of four-wave mixing signals with time resolution in these polarization configurations, which, in the limit of ultranarrow pulses, reduce to analytic functions of time and excitation and sample parameters. These equations are used to analyze signal characteristics in every polarization configuration. The results give a correct picture of biexciton effects and the polarization dependence of coherent four-wave mixing in GaAs quantum wells.

D. S. Chemla

John Erland, K.‐H. Pantke, Vygantas Mizeikis +2 more

Current issues in the study of light-matter interactions are coherence and quantum interference. With ultrafast nonlinear spectroscopy such as transient four-wave mixing (TFWM) the imposed coherence on the optical excitations in e.g. GaAs multiple quantum wells has been studied. In this contribution, we study the influence of inhomogeneous broadening on quantum beats observed by spectrally resolved TFWM. In artificially grown semiconductor structures as e.g. quantum wells, inhomogeneities due to interface-disorder has, up till now, been inevitable. In the experiments, the light-hole exciton (lhx) and the heavy-hole exciton (hhx) in a 100 Å GaAs multiple quantum well are excited simultaneously with 150 fs pulses from a self mode-locked Ti:sapphire laser. The spectral profile is shown in the inset of Fig. 1.

Duncan G. Steel, Steven T. Cundiff, H. Wang

Duncan G. Steel, Hailin Wang, Michael D. Webb +2 more