由宽波段多光子作用产生的锂分子高位态受激辐射

本文报道了以６２０．６￣６６５．０ｎｍ范围内任意波长激光作用下产生的锂分子高位态紫外扩散带受激辐射的实验结果,在锂分子－原子系统中,由激光双光子激发、并通过碰撞能量转移过程以及多光子电离复合过程使锂分子高位态获得布居,从而得到紫外区扩散受激辐射,该辐射来自较高的某个三重态向低排斥态ａ＾３Σｕ＾＋的跃迁的结果。文中对有关的辐射特性及激发机制进行了详细的分析和讨论。     

钾原子中多种受激辐射参与的混频过程

当双原子共振激发钾原子于６Ｓ能级时,由光泵受激辐射和电离复合受激辐射参与的六波或四波混频,产生了位于紫外和紫区的诸多相干辐射、文中对多种混频机制进行了分析和讨论,并对所测得的相干辐射线进行了标识．     

受激布里渊散射对纳秒激光脉冲光限幅规律

 研究了受激布里渊散射对纳秒激光脉冲的光限幅效应。针对四氯化碳介质研究了受激布里渊散射对2ns激光脉冲的光限幅和稳定输出能量的特性,给出了光限幅特性及输出能量与光限幅介质的结构参数之间的关系。对于输入能量波动范围在 13%的激光脉冲,实验获得输出能量波动范围为 7%,与理论分析的结果基本符合。     

受激布里渊散射对纳秒激光脉冲光限幅规律

研究了受激布里渊散射对纳秒激光脉冲的光限幅效应。针对四氯化碳介质研究了受激布里渊散射对2ns激光脉冲的光限幅和稳定输出能量的特性,给出了光限幅特性及输出能量与光限幅介质的结构参数之间的关系。对于输入能量波动范围在 13%的激光脉冲,实验获得输出能量波动范围为 7%,与理论分析的结果基本符合。     

100 μm FEL受激辐射光学诊断

 给出了基于L波段射频直线加速器运行的100 μm FEL自发辐射与受激辐射实验的光学诊断结果,简要介绍了100 μm FEL的光腔准直系统。针对100 μm FEL实验研究的基本要求,对辐射信号的波长光谱、功率能量和脉冲结构等主要参数进行了测量诊断。利用远红外光栅谱仪和锗掺镓光电探测器组成的测量系统,对辐射光的宏脉冲信号进行分光,测量得到了辐射光信号的波长光谱和宏脉冲波形,测得受激辐射中心波长约为115 μm;利用标定过的锗掺镓探测器对辐射信号的功率能量进行了测量,测得单个宏脉冲的功率约为mW量级,能量为nJ量级。     

光腔中两组分玻色-爱因斯坦凝聚体的受激辐射特性和量子相变

研究了单模光腔中两组分玻色-爱因斯坦凝聚的基态性质和相关的量子相变.通过利用自旋相干态变换将等效赝自旋哈密顿算符对角化并求得基态能量泛函.基态能量泛函对其经典场变量进行变分并取极小值,得到光子数解和相边界曲线.通过稳定性讨论发现系统除了出现正常相和超辐射相之外,还得到了多稳的宏观量子态;受激辐射来自于原子数反转的集体态,单组分的Dicke系统中并没有此现象;受激辐射只能从一组分的原子中产生,而另外的仍保持在普通超辐射状态.通过调整相关的原子-场耦合强度和频率失谐,超辐射和受激辐射态的顺序可以在原子的两个组分之间互换.     

水的低频受激拉曼散射

利用532 nm的脉冲激光进行了水的受激拉曼散射研究. 水的低激发光能量下主要表现为受激Stocks和反Stocks 3426 cm^-1谱线; 在能量大于140 mJ时出现低频率313 cm^-1受激Stocks谱线, 同时出现后向3389和3268 cm^-1 的受激Stocks谱线. 实验结果表明, 在较强的激光作用下, 水的结构表现为冰的Ⅷ相.     

水的低频受激拉曼散射

利用532 nm的脉冲激光进行了水的受激拉曼散射研究. 水的低激发光能量下主要表现为受激Stocks和反Stocks 3426 cm^-1谱线; 在能量大于140 mJ时出现低频率313 cm^-1受激Stocks谱线, 同时出现后向3389和3268 cm^-1 的受激Stocks谱线. 实验结果表明, 在较强的激光作用下, 水的结构表现为冰的Ⅷ相.     

VPE ZnSxSe1-x外延膜中的自发和受激辐射

本文首次报道了VPE ZnSxSe1-x外延膜在77K时起因于激子和激子(Ex-Ex)散射的自发辐射和受激辐射,研究了Ex-Ex散射发光的位置和强度与激发密度的关系,分析了受激辐射的光子能量比自发辐射稍低的原因.     

水中受激拉曼散射的能量增强及受激布里渊散射的光学抑制

为提高液体介质中受激拉曼散射的输出能量,提出了通过温度调控来抑制受激布里渊散射的方法,设计了532 nm多纵模宽带脉冲激光泵浦的受激拉曼散射发生系统,测量了不同温度下水中前向受激拉曼散射及后向受激布里渊散射的输出能量,分析了水温、泵浦激光线宽及热散焦效应对受激拉曼散射输出能量影响的物理机制.实验结果表明:通过降低水温可实现对受激布里渊散射过程的有效抑制,同时减小热散焦效应带来的光束畸变,从而有效提高受激拉曼散射的输出能量.研究结果对液体介质中的受激拉曼散射多波长转换具有重要意义.     

Dynamical study on the stimulated processes of an exciton and a biexciton in a polymer

By applying a femtosecond stimulating pulse, we theoretically study the stimulated processes of an exciton and a biexciton in a polymer within the framework of an extended Su–Schrieffer–Heeger tight-binding model. For an exciton, it is obtained that the stimulated emission and absorption between the intragap levels take place with the same probability, by which we will not get the light amplification. However, the light amplification can be realized by the stimulated emission between the intragap levels in a biexciton, which is found to have two different modes. Finally, effect of the stimulating energy and intensity on the stimulated processes is separately analyzed. These results might be of great importance for further improving the optical applications of polymers, especially for optimizing the polymer laser properties.     

Electromagnetically induced transparency in quantum dot biexciton–exciton cascaded scheme

We numerically investigated the electromagnetically induced transparency in the quantum dot biexciton–exciton scheme. Through calculating the density matrix equation in the steady state, we obtain the electromagnetically induced transparency absorption dip with different pump intensity and biexciton decay rate. The refractive index is also calculated. We analyze the biexciton energy renormalization and pump pulse intensity influencing on the EIT dip and the slow factor. The slow factor decreases from about 3000 to 2000 due to the renormalization. It shows better temperature stability for stronger confinement energy and smaller decay rate compared with quantum well.     

Correlated photons from multi-carrier complexes in GaAs quantum dots

We have studied micro-photoluminescence spectra of a self-assembled single GaAs quantum dot under 8 K. With strong pulsed excitation, the micro-photoluminescence spectrum shows bright emission lines originated from an exciton, a positively charged exciton, and a biexciton, together with weak lower energy emissions reflecting multi-excitonic structures with more carriers. We have identified the origins of these weak emission lines, and showed the existence of charged biexciton states, through single photon correlation measurements and excitation power dependence of the photoluminescence intensity. In addition, investigating the radiative recombination process of the charged biexciton, we have determined the electron–hole exchange energy in the GaAs quantum dot.     

Vector classification, doublet splitting of exciton and biexciton subbands in crystals, and selection rules for transitions between them

The analysis of experimental data on absorption, reflection, luminescence in the region of exciton and biexciton phototransitions in CdS, including P-band structure, shows that there is doubled, contrary to known theory, number of free exciton and biexciton states. This discreapancy is removed in the vector model of these states presented in this paper. The selection rules for transitions between exciton (biexciton) states in crystals taking into consideration their L-T splitting are obtained. The spectra of stimulated FIR radiation on excitonic transitions in CdS, previously obtained experimentally, well fit to these selection rules.     

Electronic structure and absorption spectrum of biexciton obtained by using exciton basis

We approach the biexciton Schrödinger equation not through the free-carrier basis as usually done, but through the free-exciton basis, exciton–exciton interactions being treated according to the recently developed composite boson many-body formalism which allows an exact handling of carrier exchange between excitons, as induced by the Pauli exclusion principle. We numerically solve the resulting biexciton Schrödinger equation with the exciton levels restricted to the ground state and we derive the biexciton ground state as well as the bound and unbound excited states as a function of hole-to-electron mass ratio. The biexciton ground-state energy we find, agrees reasonably well with variational results. Next, we use the obtained biexciton wave functions to calculate optical absorption in the presence of a dilute exciton gas in quantum well. We find an asymmetric peak with a characteristic low-energy tail, identified with the biexciton ground state, and a set of Lorentzian-like peaks associated with biexciton unbound states, i.e., exciton–exciton scattering states. Last, we propose a pump–probe experiment to probe the momentum distribution of the exciton condensate.     

浅ZnCdSe/ZnSe量子阱的光泵受激发射

本文主要研究浅ZnCdSe/ZnSe单量子阱在77K温度下的光致发光。在不同激发密度下,讨论了该结构的发光机制,把77K温度下的受激发射归结为是激子-激子散射所引起的。文中还分析了在浅ZnCdSe/ZnSe量子阱中能够实现与激子相关的受激发射的原因。     

Coherent optical writing and reading of the exciton spin state in single quantum dots

We demonstrate a one-to-one correspondence between the polarization state of a light pulse tuned to neutral exciton resonances of single semiconductor quantum dots and the spin state of the exciton that it photogenerates. This is accomplished using two variably polarized and independently tuned picosecond laser pulses. The first "writes" the spin state of the resonantly excited exciton. The second is tuned to biexcitonic resonances, and its absorption is used to "read" the exciton spin state. The absorption of the second pulse depends on its polarization relative to the exciton spin direction. Changes in the exciton spin result in corresponding changes in the intensity of the photoluminescence from the biexciton lines which we monitor, obtaining thus a one-to-one mapping between any point on the Poincaré sphere of the light polarization to a point on the Bloch sphere of the exciton spin.     

Pressure-induced threshold optical pump intensity in a CdTe/ZnTe quantum dot

Pressure-induced binding energies of an exciton and a biexciton are studied taking into account the geometrical confinement effect in a CdTe/ZnTe quantum dot. Coulomb interaction energy is obtained using Hartree potential. The energy eigenvalue and wave functions of exciton and the biexciton are obtained using the self-consistent technique. The effective mass approximation and BenDaniel-Duke boundary conditions are used in the self-consistent calculations. The pressure-induced nonlinear optical absorption coefficients for the heavy hole exciton and the biexciton as a function of incident photon energy for CdTe/ZnTe quantum dot are investigated. The optical gain coefficient with the injection current density, in the presence of various hydrostatic pressure values, is studied in a CdTe/ZnTe spherical quantum dot. The pressure-induced threshold optical pump intensity with the dot radius is investigated. The results show that the pressure-induced electronic and optical properties strongly depend on the spatial confinement effect.     

ZnCdTe-ZnTe多量子阱的光泵受激发射

本文报导了ZnCdTe-ZnTe多量子阱的受激发射机理.阈值时(J_th)受激发射峰相对于激子吸收峰的能量差(19meV)与激子束缚能接近.激发光强度在3J_th～4.8J_th之间变化时,该能量差随激发光强度的变化规律与激子-激子散射过程的理论结果符合得很好,从而把该材料在上述激发光强内的受激发射机理归结为激子-激子散射过程.     

Biexcitonic absorption in a disk-shaped GaN quantum dot

The present work investigates the nonlinear optical properties of a GaN quantum dot in the disk limit via the exciton and biexciton states using the compact density matrix formalism. Based on this model, we calculate the ground state energy of the exciton and biexciton states by the variation method, within envelope function and effective mass approximations. Linear and nonlinear optical absorption (α ⁽¹⁾, α ⁽³⁾) and oscillator strengths attributed to the optical transitions are obtained. The details of the behaviour of α ⁽¹⁾ and α ⁽³⁾ around the resonance frequencies and for different quantum dot geometries are presented. It is found that the size of quantum dot and the optical intensity have a remarkable effect on the optical absorption, and the biexcitonic two-photon absorption coefficient(K ₂) has also been calculated in this system. The results show that this parameter is strongly affected by the size of the quantum dot.