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Physica Scripta

Ultrafast nonlinear optics in GaAs/AlGaAs quantum wells

J. M. Hvam, D. Birkedal, Vadim G. Lyssenko, John Erland, C. B. Sørensen

Published Jan 1, 1994• 9 citations
Publisher

Abstract

By degenerate four-wave mixing experiments in a two-beam geometry, we have investigated the initial coherence and dephasing of quasi two-dimensional excitions and biexcitons in GaAs multiple quantum wells. The dephasing has contributions from phonon scattering, interface-roughness scattering and exciton-exciton scattering. Inhomogeneous broadening and generation of coherent wavepackets play a significant role in the coherent exciton dynamics. The incoherent exciton dynamics, diffusion and recombination, is studied by three-beam transient grating experiments. A significant difference in the interface roughness scattering of coherent and incoherent (thermalized) excitons is observed.

DOI
10.1088/0031-8949/1994/t54/045

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The interface roughness on a nanometer scale plays a decisive role in dephasing of excitons in GaAs multiple quantum wells. The excitonic four-wave mixing signal shows a free polarization decay and a corresponding homogeneously broadened line from areas with interface roughness on a scale larger than the exciton diameter. A photon echo and a corresponding inhomogeneously broadened line are observed from areas of interface roughness on a scale less than the exciton diameter. In the present study we observe both mechanisms simultaneously, and are able to clearly distinguish between the two mechanisms by spectrally resolving the transient four-wave-mixing signal.
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