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AIP conference proceedings

Dephasing of Excitons in ZnSe Quantum Wells Using Ultrashort Excitation Pulses

S. Tripathy, Pradeep Bajracharya, A. Kabir, Hans Peter Wagner

Published Jan 1, 2007• 0 citations
Publisher

Abstract

We report on the decoherence of excitons in ZnSe single quantum wells by intensity dependent four‐wave‐mixing (FWM) experiments using 30 fs pulses. The FWM traces at the 11h exciton transition reveal marked quantum beats and a fast decay at pulse overlap that is attributed to a destructive interference of the polarization wavepacket and to an effective diffraction of the exciton polarization at an electron‐hole‐pair density grating. Three‐pulse FWM experiments are performed to study the formation of excitons from this electron‐hole‐pair grating.

DOI
10.1063/1.2729944

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We report on the decoherence of excitons in ZnSe single quantum wells by intensity dependent four‐wave‐mixing (FWM) experiments using 30 fs pulses. The FWM traces at the 11h exciton transition reveal marked quantum beats and a fast decay at pulse overlap that is attributed to a destructive interference of the polarization wavepacket and to an effective diffraction of the exciton polarization at an electron‐hole‐pair density grating. Three‐pulse FWM experiments are performed to study the formation of excitons from this electron‐hole‐pair grating.
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Abstract We investigate coherences between σ+ and σ− exciton states in a 10 nm thick ZnSe/ZnMgSe single quantum well by spectrally resolved three‐pulse degenerate four‐wave mixing using circularly polarized 100 fs pulses. Intensity dependent measurements are performed to study the influence of exciton–exciton scattering on their dephasing rates. The experiments reveal nearly equal zero‐density dephasing rates for coherences between σ+ and σ− heavy‐ and/or light‐hole exciton states as compared to the dephasing rate of the interband coherence between these states and the ground state. The measurements also demonstrate that exciton‐exciton scattering destroys the coherence between heavy‐ and light‐hole excitons about three times more effectively than the coherence between σ+ and σ− heavy‐hole excitons. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
The coherent control of excitonic and biexcitonic polarization in pulse-transmission and four-wave-mixing (FWM) experiments is analysed with real time resolution. As a model system a ZnSe single quantum well is exclusively excited at the heavy-hole exciton and exciton–biexciton resonance. In pulse-transmission experiments the coherent control of excitonic polarization is shown for low excitation intensities. At elevated excitation intensities the dephasing time of the polarization is found to be strongly dependent on the relative phase of two phase-locked laser pulses which perform the coherent manipulation of the polarization. In FWM experiments the separate coherent control of the excitonic and biexcitonic FWM polarization is demonstrated which enables a coherent manipulation of the amplitude and phase of exciton–biexciton beats which are observed on the FWM polarization transients.