球形ZnS/CdSe/ZnS核壳壳量子点的三阶极化率参量相关特征

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导出了三层球型量子点的三阶非线性光学极化率(自聚焦)的解析表达式.通过数值计算,分析了ZnS/CdSe/ZnS球型核壳结构量子点的三阶极化率(自聚焦)与量子点尺寸和入射光频率之间的关系.结果显示,量子点尺寸增大时,自聚焦效应三阶极化率(自聚焦)的峰值高度增大,峰值位置红移.本文的讨论为实验研究和实际应用提供了理论依据,对于光电器件的研究和改进有参考价值.     

球形ZnS/CdSe/ZnS核壳壳量子点的三阶极化率参量相关特征

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导出了三层球型量子点的三阶非线性光学极化率(自聚焦)的解析表达式.通过数值计算,分析了ZnS/CdSe/ZnS球型核壳结构量子点的三阶极化率(自聚焦)与量子点尺寸和入射光频率之间的关系.结果显示,量子点尺寸增大时,自聚焦效应三阶极化率(自聚焦)的峰值高度增大,峰值位置红移.本文的讨论为实验研究和实际应用提供了理论依据,对于光电器件的研究和改进有参考价值.     

球形CdSe/ZnS核壳量子点的三阶极化率参量相关特征

在有效质量近似下,利用密度矩阵理论,采用无限深势阱模型,推导出了CdSe/ZnS核壳结构球形量子点的非线性光学中自聚焦效应的三阶极化率表达式。通过数值计算,分析了球形CdSe/ZnS核壳结构量子点的三阶极化率与量子点尺寸和入射光频率之间的关系。并对结果作出了必要的理论解释。     

非对称耦合量子阱的吸收非线性增强

基于V 形三能级模型运用密度矩阵方程推导了非对称耦合量子阱三阶光学非线性极化率. 具体分析了三阶吸收非线性效率（三阶光学非线性极化率与线性吸收系数之比）随阱间电子相干振荡频率的变化规律. 理论结果表明：三阶吸收非线性效率对阱间电子相干振荡频率相当敏感，当阱间电子相干振荡频率增大时三阶吸收非线性效率显著增强，而当阱间电子相干振荡频率为零时，这种非线性效率类似于单量子阱情况. 与单量子阱相比，对于已设计好的非对称耦合量子阱结构其突出特征表现在，其非线性吸收与色散特性可经由沿材料生长方向偏压进行控制. 据此，我们预期利用这种非对称耦合量子阱结构能设计成光通信中的光限幅器和可控克尔光开关.     

AlGaN/GaN抛物量子点的尺寸相关三阶非线性极化率研究

在有效质量近似框架下,通过求解AlxGa1－xN/GaN自组织圆柱形量子点的薛定谔方程,计算了量子点中导带电子在两个正交方向：Z‖和Z⊥方向上产生的三阶非线性极化率.计算中,电子的运动受到自组织量子点的抛物型束缚势和内建压电场的影响.计算表明,量子点的三阶非线性极化率的数量级达到了10－14m2/V2.进一步在Z‖和Z⊥方向上,考察了三阶非线性极化率与两个方向上的抛物束缚势的频率ωp、ωz,量子点的高度L,半径R,Al的含量x之间的关系.     

CdSe量子点的线性和非线性光学特性

主要从实验和理论两个方面,探讨了强受限尺寸区域内不同尺寸对CdSe量子点线性和非线性光学性质的影响.用吸收光谱研究了量子点尺寸与吸收峰之间的关系,用皮秒Z扫描技术研究了共振和非共振情况下(激发光波长分别为532和1064nm),尺寸与三阶非线性极化率之间的关系.基于电子能量状态理论和局域场增强理论对量子点进行分析,得到了CdSe不同尺寸的三阶非线性效应,研究了尺寸对量子点非线性光学性质的影响.结果表明,由激发态粒子数布局改变和纳米颗粒增大引起的非线性共振增强效应相当,二者共同作用使得三阶极化率增强20倍左右,且用532nm的共振频率激发4.3nm CdSe量子点时,χ⁽³⁾具有最大值2.0×10^-11esu. 关键词： CdSe量子点 三阶非线性 Z扫描')" href="#">Z扫描 量子限域效应     

极化子效应对ZnS/CdSe柱型核壳量子点简并四波混频过程的影响

理论计算了带有极化子效应的ZnS/CdSe柱型核壳结构量子点简并四波混频的三阶极化率.在有效质量近似下,采用无限深势阱模型,导出了带有极化子效应的柱型量子点的三阶非线性光学极化率的解析表达式,解三维薛定谔方程得到电子的本征能量和波函数.分析了电子-LO声子和电子-IO声子相互作用对ZnS/CdSe核壳结构量子点简并四波混频的三阶极化率的影响.结果表明,当量子点尺寸一定时,带有极化子效应的χ(3)DFWM比没有极化子时的三阶极化率提高了近3个数量级,并且电子-LO声子的影响比电子-IO声子的影响大得多;当固定核壳量子点的阱宽而内外半径发生变化时,χ(3)DFWM的峰值随之变化,而且极化子效应影响的大小也随之发生变化.     

用近简并三波混频研究半导体掺杂玻璃的非谐振三阶非线性

用近简并三波混频实验方法对半导体CdS_0.4Se_0.6掺杂玻璃在非谐振透明区的三阶光学非线性进行了研究.该实验消除了由于双光子吸收光生载流子的非线性折射产生的五阶非线性效应,仅获得速度快的三阶光学非线性响应.研究结果表明,在非谐振透明区,CdS_0.4Se_0.6掺杂玻璃的三阶非线性极化率并不比它的基底玻璃大很多.量子尺寸效应没有有意义地提高掺杂玻璃中CdS_0.4Se_0.6微晶的三阶非线性极化率,即使较小激子吸收峰的出现也没有发现明显的变化.     

水溶性CdTe量子点的三阶光学非线性极化特性

利用超短脉冲Z扫描技术和光学Kerr效应研究了以巯基丙酸为稳定剂的CdTe量子点水溶液的三阶光学非线性极化特性. 在532nm,30ps和800nm,130fs脉冲激光激发下, 发现分别具有正负相反取值的三阶光学非线性折射率,自由载流子吸收和双光子吸收分别是这两种脉冲激光激发下三阶光学非线性吸收的起因. 测量得到CdTe量子点的三阶光学非线性极化率约为CS₂的32倍, 在520—700nm光谱区的CdTe量子点的光学响应时间小于400fs. 关键词： CdTe量子点(QDs) Z扫描 三阶光学非线性极化特性 双光子吸收     

量子盘中的三阶非线性光学极化率

利用密度矩阵方法讨论了量子盘中的三阶非线性光学极化率,导出了近共振条件下的三次揩波的解析表达式,并以GaAs量子盘为例进行了具体的计算。结果表明,GaAs量子盘中的三阶非线性光学极化率要比GaAs量子阱的大几十倍。而且,选取适当的参量,可在吸收系数相对较小的情况下获得较大的折射率。     

Polaron effects on third-harmonic generation in cylindrical quantum-well wires

Polaron effects on third-harmonic generation (THG) in cylindrical quantum wires with a finite confining potential are investigated. The THG coefficient is obtained by using the compact-density-matrix approach and an iterative method, and the numerical results are presented for GaAs/AlAs cylindrical quantum wires. The results show that the THG coefficient is greatly enhanced and the peak shift to the aspect of high energy when considering the influence of electron-phonon interaction.     

Effects temperature,pressure and spin–orbit interaction simultaneously on third harmonic generation of wedge-shaped quantum dots

In the present paper, we have studied the effects of temperature and pressure simultaneously on the third harmonic generation (THG) of a GaAs wedge-shaped quantum dot under the influence of spin–orbit interaction (SOI). For this purpose, we have used analytical expression for THG obtained by the compact-density matrix formalism. THG has been calculated for different temperatures and pressures under SOI. According to the obtained results, it is found that (i) THG shows a red shift of peak position in the presence of SOI. (ii) THG shifts toward higher energies with increasing temperature and considering the SOI. (iii) THG moves to lower energies with increasing pressure and considering the SOI.     

Third-harmonic generation in cylindrical quantum dots in a static magnetic field

The third-harmonic generation (THG) coefficient for cylindrical quantum dots in a static magnetic field is investigated theoretically. By using the compact density-matrix approach and the iterative method, we obtain an analytical expression for the THG coefficient, and numerical calculations for typical GaAs/AlAs cylindrical quantum dots are presented. The results show that the THG coefficient can reach a magnitude of 10⁻¹⁰ m²/V ². In addition to the radius R of the cylindrical quantum dots, both the parabolic confining potential and the static magnetic field have an influence on the THG coefficient.     

Electronic and Optical Properties of a Lens Shaped Quantum Dot under Magnetic Field：Second and Third-Harmonic Generation

In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method (FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation (SHG) and third-harmonic generation (THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot.     

Electronic and Optical Properties of a Lens Shaped Quantum Dot under Magnetic Field: Second and Third-Harmonic Generation

In the present work, we have studied electronic and optical properties of a lens-shaped quantum dot under an external magnetic field. For this goal, we have calculated the energy levels and wave functions using the finite element method(FEM) for different values of magnetic field. We have also studied effect of magnetic field on second harmonic generation(SHG) and third-harmonic generation(THG) in the lens-shaped quantum dot. In this regard, we have obtained an analytic expression for the SHG and THG by a compact density matrix approach and an iterative procedure. According to the obtained results, it is found that the presence of the magnetic field affects the symmetry of the system. The SHG and THG are decreased with increasing the magnetic field. The magnetic field has a great influence on the energy levels, wave functions, the SHG and THG in a lens shaped quantum dot.     

Studies on the third-harmonic generations in cylindrical quantum dots with an applied electric field

The third-harmonic generation (THG) coefficient for cylinder quantum dots with an applied electric field is theoretically investigated. Using the compact density-matrix approach and the iterative method, we get the analytical expression of the THG coefficient, and the numerical calculations of the typical GaAs/AlAs cylinder quantum dots are presented. The results show that the THG coefficient can reach the magnitude of 10⁻⁹ m²/V ². Apart from the length L$L$ and radius R$R$ of cylindrical quantum dots, both the parabolic confining potential and an applied electric field can also influence the THG coefficient.     

Theoretical study of the optical absorption and refraction index change in a cylindrical quantum dot

Analytical expressions of the optical absorption coefficient and the change in refractive index associated with intraband relaxation in a cylindrical quantum dot are obtained by using the density matrix formalism. Energy levels in conduction band were calculated with finite confining potential in the framework of the effective-mass envelope-function theory. Numerical calculations on a typical GaAs/AlβGa1−βAs QD are performed. It is found that the absorption and refraction index change sensitively depend not only on the incident optical wave but also on the dot size and the Al mole fraction β in the AlβGa1−βAs material.     

Third-harmonic generation in two-dimensional pseudo-dot system with an applied magnetic field

Third-harmonic generation (THG) in a two-dimensional quantum pseudo-dot system with an applied magnetic field is theoretically investigated. THG coefficient is obtained by using the compact-density matrix approach and an iterative method. Numerical results are presented for typical GaAs/AlGaAs pseudo-parabolic quantum dots. The results show that the external magnetic field and the geometrical size of the pseudo-dot system have evidently influences on the THG, whereas their influences are different.     

Exciton-phonon interaction in cylindrical semiconductor quantum dots

The exciton-longitudinal optical phonon interaction is theoretically investigated for the case of polar semiconductor cylindrical quantum dots embedded in semiconductor matrix. The theory is developed within the dielectric continuum model considering the Fröhlich interaction between electrons and confined bulk longitudinal optical phonons for a configurational interaction model of quantum dot. Representative longitudinal optical phonon mode for the exciton-phonon interaction is predicted for cylindrical InAs/GaAs quantum dots.     

Polaron effects on the third-harmonic generations in cylindrical quantum dots

The effect of the electron–LO-phonon interaction on the third-harmonic generation (THG) coefficient for cylinder quantum dots with an applied electric field is theoretically investigated, the THG coefficient is obtained by using compact-density-matrix approach and iterative method, and the numerical results are presented for a GaAs cylinder quantum dots. The results show that the THG coefficient is greatly enhanced and the peak shift to the aspect of high energy when considering the influence of electron–LO-phonon interaction.