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Proceedings Paper

Mechanism of THz emission from asymmetric double quantum wells
Author(s): S. R. Andrews; Peter G. Huggard; C. J. Shaw; J. A. Cluff; R. Grey
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Paper Abstract

Impulsive optical excitation of the lowest two conduction or valence subbands of a GaAs/AlGaAs double quantum well can lead to coherent THz emission associated with quantum beating of subband states. We find that in the conduction band the emission arises from a time varying intersubband polarization generally dominated by the beating of continuum rather than bound exciton states. This is apparent in the electric field and excitation energy dependence of the frequency and amplitude of the THz radiation. Wavepackets made up of these continuum excitons have dephasing times of several picoseconds even for excitation an otpical phonon energy above the lowest subband edge. The long lived coherence in partly attributed to the small energy difference between the eigenstates, which substantially reduces the number of relevant scattering events, and partly to the very similar dispersion of the subbands which restricts dephasing by interference. The effect of interference is revealed in systems with significant dispersion of the intersubband gap. Two examples are presented: the valence band of a double well and the conduction band in the presence of an in-plane magnetic field.

Paper Details

Date Published: 9 September 1999
PDF: 9 pages
Proc. SPIE 3828, Terahertz Spectroscopy and Applications II, (9 September 1999); doi: 10.1117/12.361041
Show Author Affiliations
S. R. Andrews, Univ. of Bath (United Kingdom)
Peter G. Huggard, Univ. of Bath (United Kingdom)
C. J. Shaw, Univ. of Bath (United Kingdom)
J. A. Cluff, Univ. of Bath (United Kingdom)
R. Grey, Univ. of Sheffield (United Kingdom)

Published in SPIE Proceedings Vol. 3828:
Terahertz Spectroscopy and Applications II
J. Martyn Chamberlain, Editor(s)

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