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Nonlinear optical rectification coefficient χ 0 ( 2 ) in laterally-coupled Al x Ga 1−x As/GaAs quantum well wires with an applied electric field is theoretically investigated using the effective mass approximation as well as the numerical energy levels and wavefunctions of electrons. We find that χ 0 ( 2 ) is greatly influenced by the electric field as well as both the distance and the radius of the coupled system. A blue shift of χ 0 ( 2 ) with increasing electric field is exhibited while a red shift followed by a blue shift with increasing distance or radius is exhibited. A nonmonotonic behavior can be found in the resonant peak values of χ 0 ( 2 ) along with the increase of the electric field, the distance or the radius. One or two of the following physical mechanisms: the increased localization of the ground and first-excited states, the reduced coupling and the reduced quantum confinement effect are applied to elucidate the results above. Our results play a potential role in infrared photodetectors based on the coupled system. [ABSTRACT FROM AUTHOR]

Abstract: Linear and nonlinear intersubband optical absorption and refractive index change in asymmetrical semi-exponential quantum wells are theoretically investigated within the framework of the compact–density–matrix approach and iterative method. The wave functions are obtained by using the effective mass approximation. The energy levels are obtained by numerical method. It is found that the optical absorption coefficients and refractive index changes are strongly affected not only by σ and , but also by the incident optical intensity. [Copyright &y& Elsevier]