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Nonlinear optical rectification in symmetric coupled Al x Ga 1−x As/GaAs quantum wells with external electric field is investigated using numerical method and compact density matrix approach. Our results reveal that for the resonant peaks of optical rectification, a blue shift is exhibited for increasing electric field, while a red shift followed by a blue shift is exhibited for increasing barrier or well widths. The resonant peak values of optical rectification can reach a maximum value by an appropriate choice for the electric field, the barrier or well widths. Our studies pave the way for the design, optimization and applications of quantum-sized nonlinear optoelectronic devices. [ABSTRACT FROM AUTHOR]

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: Nonlinear optical rectification and the second-harmonic generation (SHG) in semi-parabolic and semi-inverse squared quantum wells are theoretically investigated within the framework of the compact-density-matrix approach and iterative method. The wave functions and the energy levels are obtained by using the effective mass approximation. It is found that nonlinear optical rectification coefficients and the second-harmonic generation are strongly affected not only by the confinement frequency , but also by the parameter . [Copyright &y& Elsevier]

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]

Abstract: Polaron effects on nonlinear optical rectification in asymmetrical Gaussian potential quantum wells are studied by the effective mass approximation and the perturbation theory. The numerical results show that nonlinear optical rectification coefficients are strongly dependent on the barrier hight V 0 of the Gaussian potential quantum wells, the range L of the confinement potential and the electric field F. Besides, the numerical results show that no matter how V 0, L and F change, taking into consideration polaron effects, the optical rectification coefficients get greatly enhanced. [Copyright &y& Elsevier]

Abstract: Second-harmonic generation (SHG) coefficients in asymmetrical semi-exponential quantum wells (ASEQW) are studied theoretically. The eigenfunctions and the energy eigenvalues are obtained by solving Schrödinger equation within the framework of effective mass approximation. In addition, the analytic expression of SHG coefficients is acquired by using compact-density-matrix approach and iterative method. The results show that both σ and U 0, which are parameters of the bound potential in the growth direction of ASEQW, have great influences on the magnitude and the resonant frequencies of SHG coefficients. [Copyright &y& Elsevier]

We investigate linear and nonlinear optical absorption coefficients (OACs) and refractive index changes(RICs) of a Morse quantum well when a quantum-sized metal nanoparticle is placed nearby. The exciton–plasmon coupling induces the modification of the energy interval and the relaxation rate of the Morse quantum well. The spontaneous decay rate of the Morse quantum well is also modified due to Purcell effect. These modification above reduce the magnitudes of the linear and nonlinear OACs and RICs of the Morse quantum well. More colorful results are demonstrated by controlling the size of the metal nanoparticle and the distance between the Morse quantum well and the metal nanoparticle. Our findings provide a way for manipulating the linear and nonlinear optical properties of the Morse quantum well. [ABSTRACT FROM AUTHOR]

• Exciton enhances refractive index changes (RICs) of Morse quantum wells (MQWs). • Exciton effect enhances optical absorption coefficient (OACs) of MQWs. • Al density and width parameter-dependent OACs and RICs of MQWs are revealed. • Hole mass-dependent OACs and RICs of MQWs are revealed. • Electric field effect on OACs and RICs of MQWs is revealed. Previously, much work on nonlinear optical effects in Morse quantum wells (MQWs) was based on electronic state transitions. However, exciton effect in MQWs is neglected and needs to be considered due to its great significance in determining nonlinear optical effects. Here, the variational method and the diagonalization method are utilized to acquire excitonic states in Al x Ga 1 − x As / GaAs MQWs. The exciton effect in MQWs induces an obvious enhancement of the linear and nonlinear optical absorption coefficients (OACs) and refractive index changes (RICs). The linear and nonlinear OACs and RICs are dynamically manipulated through tuning the electric field, and even are suppressed under a strong electric field. In addition, the linear and nonlinear OACs and RICs in MQWs are strongly affected by the hole mass, the width parameter and the aluminum concentration, which provides direction for obtaining desired nonlinear optical effects. [ABSTRACT FROM AUTHOR]

Abstract: A theoretical study of third-harmonic generation is performed by using the compact-density-matrix method. An electron is confined in semi-parabolic potential plus semi-inverse squared potential quantum wells. Our calculations show that the absolute value, the imaginary part and the real part of third-harmonic generation coefficients are greatly influenced by the parabolic confinement frequency and the characteristic parameter of the inverse squared potential. The relationship between the absolute value and the imaginary part as well as the relationship between the absolute value and the real part is discussed. It is found that the resonant peaks of the absolute value originate from the imaginary part and are not related to the real part. [Copyright &y& Elsevier]