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Physica Scripta

Nonlinear optical refractive index changes of GaAs/AlGaAs quantum dot under tangent-square potential

Ceng Chang

Published Mar 15, 2023• 4 citations
Publisher

Abstract

Abstract We investigate in detail the effects of some factors on the optical refractive index change (RICs) in GaAs/AlGaAs parabolic quantum dot (QD) with tangent-square potential (TSP) in our paper, such as the radius of quantum dot, the depth and width limit potential. In the first place, we increase the limit of tangent square potential in the z-direction of the system, which is based on the original parabolic QD, then the Schrödinger equation corresponding to the modified system is solved, and the expressions of different splitting energy levels and wave functions are obtained. At last, the numerical simulations indicate that these physical factors have a significant effect on the nonlinear optical performances of the tunable system.

DOI
10.1088/1402-4896/acc48c

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Abstract We investigate in detail the effects of some factors on the optical refractive index change (RICs) in GaAs/AlGaAs parabolic quantum dot (QD) with tangent-square potential (TSP) in our paper, such as the radius of quantum dot, the depth and width limit potential. In the first place, we increase the limit of tangent square potential in the z-direction of the system, which is based on the original parabolic QD, then the Schrödinger equation corresponding to the modified system is solved, and the expressions of different splitting energy levels and wave functions are obtained. At last, the numerical simulations indicate that these physical factors have a significant effect on the nonlinear optical performances of the tunable system.
The optical properties of quantum dots (QDs) in modified Möbius squared (MMS) potential are studied. To obtain the energy expressions and the wave functions, we solved the Schrödinger equation by using Nikiforov-Uvarov (NU) method. We investigated the linear, third-order nonlinear and total absorption coefficients (AC) and refractive index changes (RIC) using the density matrix. The numerical results show that the structure parameters and optical intensity have a strong influence on AC and RIC.
In this present study, we have theoretically investigated the effect of applied external electric field and non-resonant intense laser field, as well as the adjustable physical parameters (A, M, and η) of the system, on the linear and nonlinear of GaAs/GaAlAs cylindrical quantum dot. The confinement potential of the quantum dot is composed of the axial potential with a Razavy-type quantum well in the z-direction, and the cylindrical-type potential in the radial direction. To achieve this goal, the wave functions, and the corresponding eigenvalues of the electron are investigated by resolving the time-independent Schrödinger equation using the diagonalisation technique in terms of the effective mass approximation. The linear and nonlinear optical properties’ expressions have been calculated with the help of the compact density matrix method. Our numerical results show that by changing the A, M, and η parameters, we can see a blueshift or redshift in the total optical absorption coefficients (TOACs) and relative refractive index changes (RRICs). Additionally, they are redshifted, and their extrema increase as the radius increases. The increase in electric field or laser field intensities generates a strong displacement of the resonant peak position towards the higher energies, diminishes the TOACs magnitude, and shrinks RRICs extrema. The model potential used in the computation is important, and the study of it will be practical in the development and research of nanostructures systems.
The effect of geometrical anisotropy is numerically investigated on the linear and nonlinear optical refractive index changes of a GaAs quantum dot which is located at the center of a Ga1-xAlxAs cylindrical nano-wire. The finite difference approximation has been used for obtaining energy eigenvalues and corresponding wave functions. Also, the compact density matrix formalism is applied to investigate linear, third order nonlinear and total optical refractive index (RI) changes. The optical properties are calculated as a function of the incident photon energy for different ellipsoid aspect ratio and dot radius. The results clearly reveal that the dot anisotropy plays an important role in determining the magnitude of nonlinear RI changes which enable us to adjust saturation condition. We also found that the dot anisotropy shifts optical spectrum towards both lower and higher energies which depend on the shape of dot (spherical, prolate or oblate quantum dot) and dot radius.
In the frame of quantum mechanics,the equation to describe the particle motion in Tan2x quantum well is reduced to the hypergeometric equation.The eigenvalue and the eigefunction are obtained by solving the Schrdinger equation.Analytical expressions of linear and the third-order nonlinear optical refractive index changes are obtained in Tan2x quantum well using the density matrix formalism taking into account the intrasubband relaxation.The linear and the third-order nonlinear refractive index changes are calculated.The results show that the refractive index changes depend on the shape of the well,the tunnel bandwith and the optical intensity.Numerical results are presented for a typical GaAs/AlGaAs Tan2x quantum well.
By using the compact density matrix approach and displacement harmonic variant and numerical calculation methods,the linear and nonlinear intersubband refractive index changes(RICs) in a semi-parabolic quantum well with applied electric field were investigated in detail.Numerical calculations on GaAs were performed for the dependence of RIC on the incident optical intensity,the frequency of confined potential of the semi-parabolic quantum well and the strength of applied electric field.Results reveal that the RICs in the semi-parabolic quantum well system sensitively depend on these factors.
Abstract In our investigation, we analyzed the variations in both linear and nonlinear optical properties of the GaAs/GaAlAs single quantum well heterostructure with modified Lennard-Jones potential under the conditions where external fields and the adjustable physical parameters of the structure are changed. We get the solution of the Schrödinger equation for identifying the subband energy levels with their wave functions taking advantage of the diagonalization method, effective mass approach, and parabolic band model. As a result, we find that the changes in the applied external fields and structure parameters have effects on the total optical absorption coefficients and total relative refractive index changes. While the optical response becomes red-shifted with the increment of applied electric, magnetic and intense laser fields and the well width, it becomes blue-shifted with the increment of the well depth.