非对称量子阱中的二阶非线性光学极化率

本文主要研究了一个特殊非对称量子阱中的二阶非线性光学极化率,并且利用量子力学中的密度矩阵算符理论和迭代方法导出了二次谐波极化率的解析表达式.最后,以典型的GaAs/AlGaAs非对称量子阱为例作了数值计算.数值结果表明,较大的二次谐波极化率与系统的非对称性有关,系统的非对称性越大,二次谐波极化率越大.     

基于二次谐波产生技术的BaTiO3薄膜对称性研究

光学二次谐波产生技术是研究材料极化特性和对称性的重要工具,利用搭建的显微二次谐波产生光路,对生长在SrTiO_3衬底上的BaTiO_3薄膜样品进行了二次谐波产生测试。结果表明,BaTiO_3薄膜在面内方向具有二重旋转对称性。在四种偏振模式下测量了样品的二次谐波信号,结果表明,随着基频光入射功率的变化,二次谐波强度的图样也发生了变化。当入射光功率为7.5～7.7 mW时,信号发生突变;当入射光功率大于7.5 mW时,水平偏振出射光的二次谐波信号图样主峰减弱,次峰增强。     

非对称量子阱中非线性光学吸收系数的计算

非对称量子阱中的非线性光学效应因其潜在的实用价值而引起人们的广泛关注,而量子阱内带间的光学吸收问题对研究远红外光学探测器件具有重要的理论指导意义.以Pschl-Teller势阱为例研究了影响非对称量子阱中的非线性光学吸收系数的因素.考虑到带间的电子弛豫,用量子力学中的密度矩阵算符理论导出了Pschl-Teller势阱中的线性与三阶非线性光学吸收系数的表达式.因该势阱中有两个可调参数,通过调节系统的参数,发现该系统的非线性光学吸收系数呈规律性的变化.以典型的GaAs/AlGaAs非对称量子阱为例作了数值计算,通过调节系统的参数,数值计算结果表明,入射光强以及系统的非对称性对量子阱的非线性光学吸收系数有较大的影响,从而为实验上研究非对称量子阱的非线性光学效应提供了必要的理论依据.     

LB膜的变入射角透射光学二次谐波产生研究

给出了不同基频光和倍频光偏振态组合情况下，淀积在固体基板上的Ｌａｎｇｍｕｉｒ－Ｂｌｏｄｇｅｔｔ单分子层膜在面对入射光方向和背对入射光方向时，反射及透射光学二次谐波产生随入射角变化关系的理论公式。在此基础上，对一种芪盐ＬＢ膜样品进行变入射角的透射二次谐波产生研究。     

量子点量子阱中的三阶非线性光学特性的研究

利用紧致密度矩阵近似方法，研究了一个特殊量子点量子阱中的三阶非线性光学特性(三次谐波产生)，得到了量子点量子阱系统的三次谐波产生系数的解析表达式，而且考虑了量子点量子阱系统中的两种电子束缚态-壳层阱内与阱外两种束缚态。对CdS/HgS构成的典型的量子点量子阱进行了数值计算，得到了10^-15(m／v)^2量级的三次谐波产生系数，并且绘出了三次谐波产生系数作为量子点量子阱的尺寸和泵浦光子能量的函数曲线，最后对曲线的特征及其形成的原因进行了解析。     

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.     

GaN基薄膜半导体材料不同非线性效应的竞争关系

采用金属有机化合物化学气相沉积方法生长了未掺杂GaN,p型Mg掺杂GaN,InGaN/GaN多量子阱等薄膜半导体材料,研究了其在800 nm飞秒激光激发下的非线性光学性质.实验结果表明,在800 nm飞秒激光激发下,多光子荧光、二次谐波等非线性光学信号之间存在着竞争关系,反映出不同非线性光学信号对激发光的能量分配存在着竞争,并通过其非线性光学信号强度与激发强度之间的依赖关系进行了验证.同时,本文对其竞争机理进行了初步探究.     

电子束泵浦ZnO/ZnMgO量子阱的最佳激发电压

对不同加速电压电子束泵浦下的ZnO/Zn0.85Mg0.15O量子阱的荧光光谱进行了研究。样品利用分子束外延技术在蓝宝石衬底上生长。激子隧穿使非对称双量子阱的激发效率相对于对称阱有了明显提高。非对称阱的结构设计使最佳激发电压从对称阱的7 kV降低到了更适合器件小型化的5 kV。     

锗薄膜透射光学二次谐波研究

本文采用固定入射角，改变入射光偏振方位角的方法从实验上了研究了锗薄膜的透射光学二次谐波产生及其变化规律，并从理论上推导了产生透射二次谐波的表达式，最后拟合求得描述面谐波电流的唯象参数ａ。     

基于旋光-双反射结构的星载量子密钥分发精跟踪系统控制算法研究

研究了旋光-双反射结构作为星载量子密钥分发终端的精跟踪系统时的反射光偏振态保持情况,分析了反射光面(由入射光和反射光适量确定)不一致导致的反射光子偏振态变化情况,并计算了此时可能引入的量子误码率。根据双反射结构的特点,给出了两个反射镜法线方向与入射光、出射光矢量之间的关系,并据此提出了旋光-双反射结构的卫星精跟踪系统控制算法。     

Theoretical Study on Absorption of Magnetically Tunable Terahertz Quantum-Well Photodetectors

Because of the Zeeman splitting effect in diluted semiconductor (Zn,Cd,Mn)Se, the absorption spectrum of ZnSe/(Zn,Cd,Mn)Se quantum wells can be adjusted by magnetic field effectively. Within the effective-mass approximation, the conduction electronic structure and the absorption spectrum of ZnSe/(Zn,Cd,Mn)Se quantum wells subjected to in-plane magnetic fields are investigated. Our theoretical results show that it is possible to use the ZnSe/(Zn,Cd,Mn)Se quantum well as magnetically tunable terahertz photodetectors.     

非对称耦合量子阱ZnCdSe/ZnSe的荧光光谱与拉曼散射谱

本文研究了非对称Ⅱ -Ⅳ族耦合多量子阱Zn1-xCdxSe/ZnSe的荧光光谱和拉曼散射谱特性。实验中观察到了比较明显的量子阱荧光峰 ;在拉曼散射谱中观察到了分别对应于与ZnCdSe窄阱和宽阱的一级限制光学模LOL 和LOW 及对应于ZnSe/GaAs界面的声子和等离子体的耦合模 ,并对它们进行了简单分析。     

Growth and optical characteristics of ZnCdSe/ZnSe QWs on Si substrate with ZnO buffer

In this paper, the growth and characteristics of ZnCdSe/ZnSe quantum wells (QWs) prepared on ZnO-Si (111) templates are reported. An oriented ZnO thin film with a smooth surface was employed to be the buffer layer for the ZnCdSe/ZnSe QWs growth. Scanning electron microscopy (SEM) patterns showed that the ZnO buffer layer improved the smoothness of the ZnCdSe/ZnSe sample. Up to the 3rd longitudinal optical phonon of Zn0.56Cd0.44Se observed in Raman spectra suggests that the crystal quality of ZnCdSe/ZnSe QWs is reasonably good. The influence of quantum confinement effect on exciton characters of the QWs was also demonstrated.     

Relaxation of hot excitons in CdZnSe/ZnSe quantum wells and quantum dots

The relaxation dynamics of hot excitons was studied in (Zn,Cd)Se/ZnSe quantum wells and quantum dots. A fast population of the radiative excitonic ground state occurs for an excitation excess energy corresponding to an integer number of optical phonon energies. This is indicated by a spectrally narrow photoluminescence peak observed immediately after the exciting laser pulse. Spatial diffusion of excitons, controlled by the interaction between excitons and acoustic phonons, causes a distinct linewidth broadening with increasing delay time in quantum wells. In contrast, this process is found to be strongly suppressed in quantum dots.     

ZnCdSe/ZnSe多量子阱的生长和激子光学性质的研究

用分子束外延在GaAs衬底上生长了ZnCdSe/ZnSe多量子阱结构.利用X射线衍射(XRD)、变温度PL光谱和ps发光衰减等研究了ZnCdSe/ZnSe多量子阱结构和激子复合特性.由变温PL光谱讨论了随温度升高辐射线宽展宽和辐射复合效率降低的机理.     

Intersubband resonant enhancement of the nonlinear optical properties in asymmetric (CdS/ZnSe) based quantum wells

In this work, the linear and nonlinear optical properties are studied theoretically in asymmetric (CdS/ZnSe/BeTe)/(ZnSe/BeTe) quantum wells. The electronic states are calculated using the envelope wave function approximation and the intersubband transition energies are studied as a function of CdS and ZnSe well thicknesses as well as doping concentration. The optimum parameters carrying out the transition energy 0.8 eV (1.55 μm wavelength) are given. Results are presented for the linear, the third order nonlinear optical absorption and the refractive index changes in the studied heterostructure. Results show that the changes in the linear and the third order nonlinear optical absorption as well as refractive index change are as important as the temperature is high, the nonlinear terms must be taken into consideration especially near the resonance.     

ZnCdSe量子阱/CdSe量子点耦合结构中的激子隧穿过程

用室温光致发光谱和飞秒脉冲抽运探测方法对不同垒宽的ZnCdSe量子阱/ZnSe/CdSe 量子点新型耦合结构中激子隧穿过程进行研究，观察到激子从量子阱到量子点的快速隧穿过 程.在ZnSe垒宽为10nm, 15nm, 20nm时，测得激子隧穿时间分别为1.8ps, 4.4ps, 39ps. 关键词： ZnCdSe量子阱 CdSe量子点 激子 隧穿     

LO-phonon assisted tunneling from spatially direct to indirect exciton in semimagnetic double quantum well structures

Relaxation from spatially direct to the spatially indirect exciton through ZnSe barriers of different thicknesses is investigated in (ZnCdMn)Se/ZnSe/(ZnCd)Se asymmetric double quantum wells by use of magneto-optical steady-state photoluminescence (PL) and PL excitation (PLE) experiments. The 1-LO-phonon scattering has been found to be the relevant mechanism for effective electron and hole tunneling.     

Photoinduced charge redistribution and its influence on excitonic states in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures

The photoinduced charge redistribution in Zn(Cd)Se/ZnMgSSe/GaAs quantum-well heterostructures under different conditions of optical excitation has been investigated using scanning probe microscopy and optical spectroscopy in the temperature range from 5 to 300 K. Excitation of the samples by radiation with a photon energy greater than the band gap of Zn(Cd)Se leads to the accumulation of electrons in quantum wells, which is detected using scanning spreading resistance microscopy. For moderate excitation densities (up to 25 W/cm²) and at temperatures ranging from 80 to 100 K, the density of a quasi-two-dimensional electron gas formed in quantum wells is several orders of magnitude higher than the density of electron-hole pairs generated by the excitation radiation. The excess electron concentration in the quantum well leads to a broadening of the exciton resonances and to an increase in the relative intensity of the donor-bound exciton emission line and also determines the increase in the luminescence quantum yield with increasing excitation intensity. An additional illumination with a photon energy less than the band gap of Zn(Cd)Se decreases the concentration of excess electrons in quantum wells. The influence of the additional illumination is observed at a temperature of approximately 100 K and almost completely suppressed at 5 K. The obtained results are explained in terms of the formation of a potential barrier for electrons at the ZnMgSSe/GaAs interface and by the specific features of recombination processes in the electron-hole system containing impurity centers with different charge states.     

Time-resolved photoluminescence and steady-state optical investigations of a Zn1−x Cd x Se/ZnSe quantum well

Il Nuovo Cimento D - We report on time-integrated and time-resolved optical experiments performed on a 26 Å thick Zn0.85Cd0.15Se/ZnSe quantum well, for temperatures in the 10–200 K...