极化子效应对非对称量子阱中光吸收系数的影响(英文)

从理论上研究子电子-声子相互作用对Morse量子阱中光吸收系数的影响,首先利用微扰论方法求出考虑极化子效应时的电子波函数和能级,然后利用密度矩阵和迭代法得到光吸收系数的解析表达式,最后以典型的GaAs/AlGaAs Morse量子阱为例进行数值计算。结果表明,极化子效应使光吸收系数比仅考虑电子的情况增大了,并且在相同光强的情况下吸收饱和现象更明显;极化子效应的影响随着阱的非对称性的增强而增大;电声相互作用对电子能级的修正导致光吸收系数峰值向高能方向偏移。     

磁场中耦合量子线的三阶非线性光学吸收率

本文研究了磁场中耦合量子线的三阶非线性光学吸收率,并且利用密度矩阵算符理论导出了三阶非线性光学吸收率的解析表达式.最后,以GaAs/Al_xGa_1-xAs耦合量子线为例作了数值计算,并绘出了三阶非线性光学吸收率与磁场B,光子能量h-ω以及间隔D之间的依赖关系.     

The correlation energies and nonlinear optical absorptions of an exciton in a disc-like quantum dot

Using exact diagonalization techniques, the low-lying states of an exciton, and the linear and nonlinear optical absorptions in a disc-like quantum dot are theoretically studied. The numerical results for the typical GaAs material show the so-called quantum size effect. Also, our study is restricted on the transition between the S state (L = 0) and the P state (L = 1). The optical absorption coefficients are greatly enhanced because of the induced size confinement. Meantime, we find that the total optical absorption coefficient is about two times bigger than that obtained by without considering exciton effects. Additionally, the optical absorption saturation intensity can be controlled by the incident optical intensity I.     

Optical absorptions of an exciton in a quantum ring: Effect of the repulsive core

We study the optical absorptions of an exciton in a quantum ring. The quantum ring is described as a circular quantum dot with a repulsive core. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The linear, third-order nonlinear and total optical absorption coefficients have been examined with the change of the confinement potential. The results show that the optical absorptions are strongly affected by the repulsive core. Moreover, the repulsive core can influence the oscillation in the resonant peak of the absorption coefficients.     

Absorption Spectra and Refractive Index Changes of an Exciton in a Core/Shell Quantum Dot

The absorption spectra and the refractive index changes are calculated theoretically for an exciton in a core/shell quantum dot. The advantage of our methodology is that one can investigate the influence of the repulsive core by varying two parameters in the confinement potential. The dimensionality effect of exciton quantum dots on the optical absorptions has been studied. It has been found that in the same regime, the optical absorption intensities of excitons are much smaller for the core/shell quantum dots than for the two-dimensional quantum rings. The linear and the nonlinear optical absorption coefficients and refractive index changes have been examined with the change of the confinement potential. The results show that the optical absorptions and the refractive index changes are strongly affected by the repulsive core of core/shell quantum dots. Moreover, the calculated results also reveal that as the inner radius increases, the peak values of the absorption coefficients and the refractive index changes of an exciton will show the optical Aharonov–Bohm oscillation in core/shell quantum dots.     

激子效应对双曲型量子线中非线性光学吸收率的影响

本文研究了双曲型量子线的三阶非线性光学吸收率,着重研究了激子对其影响,并且利用密度矩阵算符理论导出了三阶非线性光学吸收率的解析表达式。最后,以A1GaAs/GaAs双曲型量子线为例作了数值计算。数值结果表明,当线宽增加时,激子效应对三阶非线性光学吸收率的影响越来越弱,特别是,当线宽接近于扩散长度时,激子效应将显着减弱。     

加偏置电场的双曲线量子阱中线性与三阶非线性光学吸收系数的计算

利用紧致密度矩阵近似方法,研究了加偏置电场双曲线量子阱中的线性与三阶非线性光学吸收系数. 得到了该系统中的线性与三阶非线性光学吸收系数的解析表达式.分析了势阱的形状、外加电场的大小以及入射光场的强度对吸收系数的影响规律. 文章以典型的AlxGa1－xAs/ GaAs双曲线量子阱为例作了数值计算.结果表明：随着势阱宽度的增加,系统的吸收系数将减小;随着外加电场的增加,系统的非对称性增加,系统的吸收系数将增加;随着外加光场强度的增加,系统的吸收系数将减小,并且当光强增加到一定值时会出现明显的饱和吸收现象,这一结论为进一步的实验研究提供了相应的理论依据.     

Nonlinear intersubband optical absorption in semiparabolic quantum wells

The linear and third-order nonlinear optical absorptions in semiparabolic quantum wells are studied in detail. Analytic formulas for the linear and third-order nonlinear optical absorption coefficients are obtained using the compact density matrix approach. Based on this model, numerical results are presented for typical GaAs/AlGaAs semiparabolic quantum wells. The results show that the factors of the incident optical intensity and the semiparabolic confinement frequency have great influences on the total optical absorption coefficients.     

Optical properties of an off-center hydrogenic impurity in a spherical quantum dot with Gaussian potential

Optical absorption coefficients and refractive index changes associated with intersubband transition of an off-center hydrogenic impurity in a spherical quantum dot (QD) with Gaussian confinement potential are theoretically investigated. Our results show that the optical absorption coefficients in a spherical QD are 2–3 orders of magnitude higher than those in quantum wells and are 2–3 orders smaller than those in a disk-like QD. It is found that the optical absorptions and the optical refractive index are strongly affected not only by the confinement barrier height, dot radius but also by the position of the impurity.     

Intersubband optical absorptions of a two-electron quantum ring

In this Letter, the optical properties of a quantum ring with two electrons are studied. Its effective-mass Hamiltonian matrix was diagonalized with numerical methods, followed by the calculations of a number of optical quantities. We have found that the intersubband optical absorptions strongly depends on the ring radius, electron-electron interaction, and the incident optical intensity. We also found that the spin-singlet states are more sensitive to ring radius than the spin-triplet states.     

Optical anisotropy of a donor in ellipsoidal quantum dots

A system of an electron with a hydrogenic impurity confined in anisotropic quantum dots with ellipsoidal shape has been investigated. The linear and nonlinear optical absorptions as well as refractive index changes associated with intersubband transitions has been calculated. The results are presented as a function of the incident photon energy. The results show that the optical properties of a donor in ellipsoidal quantum dots are strongly affected by the anisotropy degree and the dot size. The dot anisotropy is shown to play a fundamental role in determining the dot properties.     

A study of nonlinear optical properties of a negative donor quantum dot

In this paper, we studied the nonlinear optical properties of a negative donor center (D⁻) in a disk-like quantum dot (QD) with a Gaussian confining potential. Calculations are carried out by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. A detailed investigation of the linear, third-order nonlinear, total optical absorptions and refractive index changes has been carried out for the D⁻ QD and the D⁰ QD. The linear, third-order nonlinear, total optical absorptions and refractive indices have been examined for a double-electron QD with and without impurity. Our results show that the optical absorption coefficients and refractive indices in a disk-like QD are much larger than their values for quantum wells and spherical QDs and the nonlinear optical properties of QDs are strongly affected not only with the confinement barrier height, dot radius, the number of electrons but also the electron-impurity interaction.     

外电场对直接带隙Ge量子阱中的光学性质的影响

在有效质量近似下,考虑到外电场的影响,详细研究了直接带隙Ge/GeSi量子阱中带间光跃迁吸收系数和阈值能量随量子阱阱宽,外电场强度的变化情况。结果表明：随着外电场的增强,带间光跃迁吸收强度会逐渐减弱,阈值能量减小,吸收曲线向低能方向移动,出现了红移现象。此外,当量子阱比较大时,外电场对量子阱中带间光跃迁阈值能量的影响更加明显。     

镶嵌在氢化氮化硅中纳米非晶硅粒子光吸收的模拟

采用量子限制效应模型对镶嵌有纳米非晶硅粒子的氢化氮化硅薄膜的光吸收进行了理论模拟,探讨了由吸收谱分析给出该结构薄膜光学参数的方法,并通过对不同氮含量样品的讨论给出了量子限制效应和纳米硅粒子表面的结构无序对薄膜光吸收特性的影响规律。分析结果表明,随氮含量的增加,薄膜有效光学带隙增大,该结果与薄膜中纳米硅粒子平均尺寸的减小引起的量子限制效应的增强相关,而小粒度纳米硅粒子比例增加所引入的较高微观结构无序度和较多缺陷将会导致薄膜低能吸收区吸收系数增加。     

Excited-state absorptions of an exciton confined in a quantum dot

The optical absorptions of an exciton with the higher excited states in a disc-like quantum dot are investigated. Calculations are made by using the method of numerical diagonalization of Hamiltonian matrix within the effective-mass approximation. With typical semiconducting GaAs based materials, the linear, third-order nonlinear, total optical absorption coefficients and refractive index changes have been calculated for the s–p, p–d, and d–f transitions. The results show that as the angular momentum quantum number of transitions increases, the absorption peaks shift towards lower energies and the absorption intensities increase.     

ZnS/CdSe量子点中线性和三阶非线性光吸收系数研究

在有效质量近似下,利用量子力学的密度矩阵理论,采用无限深势阱模型,从理论上研究了ZnS/CdSe柱型核壳结构量子点中线性和三阶非线性光吸收系数。导出了柱型量子点中线性和三阶非线性光学吸收系数的解析表达式,分析了该系统在不同条件下线性和三阶非线性光吸收系数与入射光频率之间的关系。改变系统的参数,该系统的光吸收系数呈规律性变化。计算结果表明:弛豫时间τ、入射光强I和壳半径R2对系统的吸收系数α有很大的影响,从而为实验上研究核壳结构量子点的非线性光学效应提供了必要的理论依据。     

Linear and Nonlinear Intersubband Optical Absorptions and Refractive Index Changes in InGaN Strained Single Quantum Wells： Strong Built-in Electric Field Effects

Considering the strong built-in electric field （BEF） effects due to the spontaneous and piezoelectric polarizations, the intersubband optical absorptions and refractive index changes for an InxGa1-xN/AlyGa1-yN strained single quantum well are studied theoretically within the framework of the density matrix method and effective-mass approximation. The linear, third-order nonlinear and total absorption coefficients and refractive index changes are calculated as a function of the incident optical intensity and photon energy. Our results show that both the incident optical intensity and the strong BEF have great influence on the total absorptions and refractive index cllanges. The results are significant for designing some important photodetectors and the photonic crystal devices with adjustable photonic band structures.     

基底对光学薄膜弱吸收测量的影响

 对表面热透镜技术测量光学薄膜弱吸收低频调制时不同基底对测量的影响进行了理论分析。用Lambda—900分光光度计测量了K9和石英基底的Ti₃O₅单层膜的吸收值,将该组样品作为定标片;用表面热透镜装置分别测量了BK7和石英空白基底及HfO₂,ZnO两组不同基底不同厚度单层膜样品的吸收。通过分析比较同一工艺条件下镀制的不同基底薄膜样品用与其同种和不同种基底定标片定标测量的结果,表明在低频测量时需要用与测量样品同种基底的定标片定标;不同厚度样品的测量结果表明,在不能严格满足热薄条件时,测量结果需引入修正值。     

Optical absorption coefficients in asymmetric quantum well

The optical absorption coefficients considering electron-phonon interaction in asymmetrical quantum wells are theoretically studied. The result shows that the optical absorption coefficients depend strongly on the parameters of quantum well. Interestingly, the theoretical values of the optical absorption coefficients obviously increase with considering the electron-phonon interaction.     

Polaron effects on the optical refractive index changes in asymmetrical quantum wells

The optical refractive index changes considering polaron effects in asymmetrical quantum wells are theoretically studied. It is shown that a pronounced optical refractive index changes dependence of the quantum well parameters can be obtained. Moreover, the theoretical values of the optical refractive index changes obviously increase when considering the electron-LO-phonon interaction.