Kangxian Guo

Second-order nonlinear optical susceptibilities in asymmetric coupled quantum wells

The second harmonic generation (SHG) in the asymmetric coupled quantum wells (ACQWs) is studied theoretically for different widths of the right-well and the barrier. The analytical expression of the SHG susceptibility is deduced by using the compact density matrix approach and the iterative method. Numerical calculations are presented for typical GaAs/AlxGa1−xAs ACQWs. The results show that the calculated SHG susceptibility in this coupled system can reach a magnitude of 10−5 m V−1, 1–2 orders higher than that in single quantum systems. Moreover, the SHG susceptibilities are not monotonic functions of the widths of the right-well and the barrier, but have complex relationships with them. The calculated results also reveal that by adjusting the widths of the right-well and the barrier respectively, a set of optimal structural parameters can be found for obtaining a strong SHG susceptibility.

Polaron effects on the third-order nonlinear optical susceptibility in a quantum disk

Theoretical investigation of polaron effects on the third-harmonic generation due to intersubband transition in a quantum disk are presented. Contributions from the bulk longitudinal optical and the surface optical phonon modes are considered separately. The analytic expression for the third-harmonic generation is derived by using the density matrix method. The numerical calculations are performed on a typical GaAs quantum disk with different incident photon energy and under various disk thicknesses. The results demonstrate that the polaron effects are quite important especially around the peak value of the third-order nonlinear optical susceptibility. The maximum χ3ω(3) under the parameters we choose is 7.8×10−16(m/V)2, which is around two order higher than that in the bulk GaAs.

Exciton effects on nonlinear electro-optic effects in semi-parabolic quantum wires

Abstract The nonlinear electro-optic effects in quasi-one-dimensional semi-parabolic quantum wires are studied, in which the exciton effects are taken into account. The analytical expression of the electro-optic co-efficient is derived by compact density-matrix approach. Finally, the numerical results are presented for GaAs/AlGaAs semi-parabolic quantum wires. The results show that the electro-optic coefficient is over two times bigger than that obtained by without considering exciton effects. Furthermore, the electro-optic coefficient is related to the relaxation time.

Dot Pattern Designing on Light Guide Plate of Backlight Module by the Method of Molecular Potential Energy

An approach for dot pattern designing on the light guide plate of backlight module is proposed in this paper. The proposed approach employs molecular potential energy model to generate random-dot patterns for light guide designed for backlight systems. The methods of developing dot patterns are various. We chose AutoCAD-VBA programme method for its visible interface. The algorithm can be divided into two steps: Firstly, an AutoCAD-VBA programme is compiled to generate random initial dot patterns, which contains 69 091 points. Secondly, a variable equilibrium distances system are found by the Mathematica software to fine tune distances among those points. At last, we have derived dot patterns which can satisfy the uniformity luminance requirement demanded by liquid-crystal displays, testing results show that the optical uniformity can reach 89.3%.

INTERSUBBAND OPTICAL ABSORPTION IN CYLINDRICAL QUANTUM DOT QUANTUM WELL

The intersubband optical absorption in cylindrical quantum dot quantum well (QDQW) for different sizes of QDQW is theoretically studied. The analytical expression of the absorption coefficient is derived by using the compact density-matrix approach and the iterative method. And the numerical calculations are presented for a typical GaAs/AlGaAs QDQW. The results obtained show that the optical absorption coefficient in the QDQW can be importantly modified by size of shell well. Moreover, they also show that the optical absorption is strongly dependent on the incident optical intensity.

Effect of hydrogenic impurity on linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot

The analytical expressions of linear and nonlinear optical absorption coefficients and refractive index changes in a quantum dot with a hydrogenic impurity are obtained by using the compact-density-matrix approach and iterative method. The wave functions and the energy levels are obtained by using the variational method. Numerical results show that the optical absorption coefficients and refractive index changes are strongly affected by the hydrogenic impurity.

Polaron effects on the third-harmonic generation in asymmetrical semi-exponential quantum wells

The polaron effects on the third-harmonic generation (THG) are investigated theoretically for electrons confined in asymmetrical semi-exponential quantum wells (ASEQWs). The analytic expression for the THG in ASEQWs is derived by using the compact-density-matrix approach and the iterative method. The numerical results are presented for GaAs/AlGaAs ASEQWs. The results demonstrate that polaron effects have an important influence on the THG. It is found that the THG is obviously increased when considering the electron-LO-interaction.

The effect of position-dependent mass on nonlinear optical absorption coefficients and refractive index changes in a quantum well

The influence of position-dependent mass (PDM) on nonlinear optical absorption (OA) coefficients and refractive index changes (RICs) is theoretically studied, within the framework of the iterative method and the compact-density-matrix approach. Through solving Schrodinger equation, the eigenfunctions and energy eigenvalues are obtained. The analytic expressions of the optical absorption coefficients and the refraction index changes are derived theoretically. The results reveal that the OA coefficients and the RICs are strongly affected by PDM, and both the peaks of them increase when considering PDM.

The Combined Influence of Hydrostatic Pressure and Temperature on Nonlinear Optical Properties of GaAs/Ga0.7Al0.3As Morse Quantum Well in the Presence of an Applied Magnetic Field

Studies aimed at understanding the nonlinear optical (NLO) properties of GaAs/Ga0.7Al0.3As morse quantum well (QW) have focused on the intersubband optical absorption coefficients (OACs) and refractive index changes (RICs). These studies have taken two complimentary approaches: (1) The compact-density-matrix approach and iterative method have been used to obtain the expressions of OACs and RICs in morse QW. (2) Finite difference techniques have been used to obtain energy eigenvalues and their corresponding eigenfunctions of GaAs/Ga0.7Al0.3As morse QW under an applied magnetic field, hydrostatic pressure, and temperature. Our results show that the hydrostatic pressure and magnetic field have a significant influence on the position and the magnitude of the resonant peaks of the nonlinear OACs and RICs. Simultaneously, a saturation case is observed on the total absorption spectrum, which is modulated by the hydrostatic pressure and magnetic field. Physical reasons have been analyzed in depth.

Polaron effects on the second-harmonic generation in asymmetrical semiexponential quantum wells

Polaron effects on the second-harmonic generation (SHG) in asymmetrical semiexponential quantum wells (ASEQWs) are investigated theoretically. By using the framework of the compact-density-matrix approach and iterative method, the analytical expression of the SHG coefficients in ASEQWs is presented. Numerical results are illustrated for a typical GaAs/AlGaAs. By considering the electron--LO--phonon interaction (ELOPI), the energy levels and the wave functions of an electron confined in ASEQWs are obtained. It is found that whether we consider the ELOPI or not, the incident photon frequency