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physica status solidi (a)

Nonlinear Effects in the Resonant Rayleigh Scattering from Quantum Well Structures

Massimo Gurioli, Franco Bogani, Daniele Capanni, A. Chiarugi, Matteo Taccola, A. Vinattieri, M. Colocci

Published Mar 1, 2000• 4 citations
Publisher

Abstract

The coherent and incoherent components of the resonant secondary emission from GaAs quantum well structures after ultrashort excitation have been studied as a function of the excitation density and inhomogeneous broadening. We find that the coherent emission saturates with the excitation power in good agreement with a simple model taking into account the exciton inhomogeneous broadening and the excitation induced dephasing.

DOI
10.1002/1521-396x(200003)178:1<453::aid-pssa453>3.0.co;2-q

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The coherent and incoherent components of the resonant secondary emission from GaAs quantum well structures after ultrashort excitation have been studied as a function of the excitation density and inhomogeneous broadening. We find that the coherent emission saturates with the excitation power in good agreement with a simple model taking into account the exciton inhomogeneous broadening and the excitation induced dephasing.
The coherent and incoherent components of the resonant secondary emission from GaAs quantum well structures after ultrashort excitation have been studied as a function of the excitation density, lattice temperature, and inhomogeneous broadening by means of interferometric correlation techniques. We find that the coherent emission is thermally quenched and saturates with the excitation power. A good agreement is found within a simple classical model based on the inhomogeneous broadening of the excitonic band, including the experimental exciton-exciton and exciton-phonon induced dephasing.
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We present a bosonic description of excitons created by means of resonant optical pumping in a quantum well in the presence of a weak disorder potential. The excitonic collective state is a Glauber coherent state, closely related to that of photons but substantially different from that of few-level models. The theory, applying to the low-density regime, is used to explain various transient linear optical experiments involving resonantly excited excitons in GaAs quantum wells. In particular, we consider coherent control of the exciton density and spin, resonant Rayleigh scattering and scattering coherent control. Our quantum mechanical approach for light emission shows that excitonic secondary emission has a coherent component, in agreement with experiments.
Phase-locked pulse pairs are used for resonant excitation of excitons confined within GaAs/AlGaAs quantum wells. The time-resolved secondary emission displays strong dependence on the relative phases of the two pulses for inter-pulse delays of the order of 1ps or less. Constructive interference is combined with an increase in the rise time of the emission following the second pulse. For longer inter-pulse delays the different phases of inhomogeneous excitons complicate the effect of the second pulse, with the apparent effect changing with time after the second pulse. To model this, the optical Bloch equations for a line of three-level systems are integrated over time and the resulting polarisations summed over a range of angles. The importance of the inhomogeneity in descriptions of coherent control of secondary emission is shown.
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Summary form only given.The coherent response of excitons in semiconductor nanostructures, as measured in four wave mixing (FWM) experiments, depends strongly on the inhomogeneous broadening of the exciton transition. We investigate GaAs-AlGaAs single quantum wells (SQW) of 4 nm to 25 nm well width. Two main mechanisms are found to be important. First, the excitation-induced dephasing FWM signal (EID), which leads to a strong dependence of the signal on the angle between the linear input polarizations. The presence of the EID in the mainly homogeneously broadened sample (25 nm) is shown by the beating between EID and two-photon coherence (TPC) at the exciton for negative delay and co-linear polarized excitation. It vanishes for cross-polarized excitation, thus excluding the importance of local-field effects.