多光子过程和自发辐射对激光诱导自电离的影响

利用反作用算符的方法,研究了一个单模激光场将原子从束缚能级激发到自电离能级的过程中,双光子过程和自发辐射过程的影响。研究结果表明:自发辐射对这种光电离过程的影响一般情况下是很小的,但光子能谱特性十分明确地表明,辐射主要来源于由态共振加强的喇曼过程;并显示了激光诱导自电离过程中的缀饰(Dressed)原子图像;双光子过程将使光电子能谱和光诱导自电离过程变得非常复杂,单光子和双光子过程所产生的光电子能谱,都具有多极大值结构。     

双分子链中非线性多激子态的动力学研究

在超快激光激发下分子聚集体内有多个激子产生.针对具有链间耦合的双分子链系统,应用密度矩阵理论,在偶极-偶极近似和算符算术平均值近似下通过求解量子主方程计算了不同双链构型下的多激子动力学过程.研究发现在光激发作用下的多激子离域在双链分子系统中,在能量表象下形成激子态能带.激子态能带的宽度和激子占据能级随双分子链构型的不同而不同.对于链间和链内均为H型排列的分子链,激子态能带变宽,激子态优先占据在高阶能级上.在不同能级下的激子具有不同的动力学演变特点.若链间耦合较强,激子态通过链间耦合传递,与分子是否直接受到激发没有直接关系,激发态在两个链内的转移周期与最近邻的链间耦合有直接关系.     

含自旋轨道耦合的三维各向同性谐振子的四类升降算符

推导出了含自旋 轨道耦合的三维各向同性谐振子的升、降算符，给出了谐振子能级的分裂情况. 关键词： 自旋-轨道耦合 谐振子 升、降算符     

V-E传能中原子荧光辐射束缚的理论处理

用Holstein型微分积分方程组描述一个含有辐射束缚的分子原子V-E传能体系的动力学过程.给出了只用一个有限项就能描述体系中原子荧光完整时间行为的约化解.进一步导出了荧光衰减速率作为传能速率常数和方程组中积分算符最大本征值的函数的解析表达.这可十分方便地用于V-E传能实验中各种常数的确定.文中的结果通过数值计算并进行了比较. 关键词：     

利用不变量本征算符求解二维耦合量子谐振子的能级间隔

目前不变量本征算符方法已成功地解决了某些量子系统哈密顿量能级问题.对于二维耦合量子谐振子,利用这一方法可以非常简捷有效地给出其能级信息,而不需要使其哈密顿量对角化.计算结果表明,不同耦合形式的二维耦合量子谐振子的能级间隔是不同的.     

非对易空间的三模谐振子能谱

在非对易空间中,用不变本征算符方法(IEO),对非耦合、坐标耦合、动量耦合三种三模谐振子系统能谱进行求解,并将求解结果与一般对易空间的能谱进行比较分析.通过比较发现,当非对易参数为零时,所求能级差还原到了与普通空间相对应的一般量子系统哈密顿量能级差,验证了推导结果的正确性;同时讨论了耦合系数对非对易空间能谱的影响. 关键词： 不变本征算符 非对易空间 三模谐振子能谱 能级差     

磁绝缘模型晶体的超荧光

Dicke命名合作自发发射为超辐射,来自非相干光激发的状态的合作自发发射叫做超荧光。我们从相互作用的双能级原子系统来研究荧光,辐射场对该系统的耦合较之原     

能谷间相互作用对量子阱Ge_(0.3)Si_(0.7)/Si/Ge_(0.3)Si_(0.7)的电子能带结构的影响

采用建立在经验赝势理论基础上的推广ｋ·ｐ方法及电流密度算符技术，计算了生长在Ｇｅ０３Ｓｉ０７（００１）衬底上的量子阱Ｇｅ０３Ｓｉ０７／Ｓｉ／Ｇｅ０３Ｓｉ０７的导带电子束缚能级．详细地研究了因能谷间相互作用而引起的能级分裂情况，同时也讨论了电子束缚能级在阱平面方向上的色散关系     

能谷间相互作用对量子阱Ge0.3Si0.7/Si/Ge0.3Si0.7的电子能带结构的影响

采用建立在经验赝势理论基础上的推广k·p方法及电流密度算符技术，计算了生长在Ge_0.3Si_0.7（001）衬底上的量子阱Ge_0.3Si_0.7/Si/Ge_0.3Si_0.7的导带电子束缚能级．详细地研究了因能谷间相互作用而引起的能级分裂情况，同时也讨论了电子束缚能级在阱平面方向上的色散关系 关键词：     

相对运动、集体振动、单粒子激发相互耦合系统输运过程的理论描述

考虑一个具有相对运动、内禀激发(包括集体振动、单粒子激发)相互耦合系统,在对相对运动做经典近似的条件下,并对内禀自由度采用与时间有关的投影算符方法,可以得到相对运动、集体振动及单粒子激发的耦合方程的一般理论形式。在一级玻恩近似和声子单粒子相互作用矩阵元的无规位相近似下,并忽略相对运动与声子单粒子之间相互作用高次项(只考虑到一次项),我们得到比较简单便于进行数值计算的耦合方程。这个理论适用于描述重离子深度非弹性散射,核裂变等核反应输运过程。     

Quantum theory of open systems based on stochastic differential equations of generalized Langevin (non-Wiener) type

It is shown that the effective Hamiltonian representation, as it is formulated in author??s papers, serves as a basis for distinguishing, in a broadband environment of an open quantum system, independent noise sources that determine, in terms of the stationary quantum Wiener and Poisson processes in the Markov approximation, the effective Hamiltonian and the equation for the evolution operator of the open system and its environment. General stochastic differential equations of generalized Langevin (non-Wiener) type for the evolution operator and the kinetic equation for the density matrix of an open system are obtained, which allow one to analyze the dynamics of a wide class of localized open systems in the Markov approximation. The main distinctive features of the dynamics of open quantum systems described in this way are the stabilization of excited states with respect to collective processes and an additional frequency shift of the spectrum of the open system. As an illustration of the general approach developed, the photon dynamics in a single-mode cavity without losses on the mirrors is considered, which contains identical intracavity atoms coupled to the external vacuum electromagnetic field. For some atomic densities, the photons of the cavity mode are ??locked?? inside the cavity, thus exhibiting a new phenomenon of radiation trapping and non-Wiener dynamics.     

Asymptotic behavior of the solutions of the Kadomtsev-Pyatviashvili equation (two-dimensional Korteweg-De Vries equation)

The asymptotic form of the solutions of the Kadomtsev-Pyatviashvili equation for t → ± ∞ is presented. The reverse problem of reconstructing the solution from its asymptotic form is also solved.     

Absorption saturation studies of Landau levels in quasi-two-dimensional systems

We report the first far-infrared linear and non-linear (saturation) magneto absorption experiments of coupled subband-Landau level excitations in a series of modulation-doped double-coupled multiple quantum-well (MQW) structures. Non-linear spectroscopy is carried out with a free electron laser. A plot of energy versus magnetic field for 4 laser lines at low intensity and high intensity is compared with linear (Fourier transform) spectroscopy at low and high temperatures. An exact numerical solution of the Schrödinger equation for this coupled system is also obtained and compared with experiments. Results show that the feature observed at high laser intensity and high temperature is due to transitions from the 1st-excited state of the coupled system to the higher excited states. Based on this, a simple 2-level model is developed, and with a layer-by-layer analysis for MQW systems, the electron lifetime of the first-excited state is obtained.     

Self-Consistent Sources Extensions of Modified Differential-Difference KP Equation

In this paper, we investigate a modified differential-difference KP equation which is shown to have a continuum limit into the mKP equation. It is also shown that the solution of the modified differential-difference KP equation is related to the solution of the differential-difference KP equation through a Miura transformation. We first present the Grammian solution to the modified differential-difference KP equation, and then produce a coupled modified differential-difference KP system by applying the source generation procedure. The explicit N-soliton solution of the resulting coupled modified differential-difference system is expressed in compact forms by using the Grammian determinant and Casorati determinant. We also construct and solve another form of the self-consistent sources extension of the modified differential-difference KP equation, which constitutes a Bäcklund transformation for the differential-difference KP equation with self-consistent sources.     

ATOMIC COHERENT POPULATION TRAPPING AND ITS APPLICATION IN A RAMAN-TYPE PHOTOIONIZATION SYSTEM WITH THREE BOUND STATES

We have studied the atomic coherent population trapping in a Raman-type, photoionization system with three bound states. The conditions for the system having two or one stable eigenstate are given. The influences of Fano asymmetric factors on the coberent population transfer are also analyzed.It is found that the property of the system having on]y one population trapping state consisting of the ground state, and one excited state, can be utilized to transfer the atomic initial population into one excited state.     

Quantum theory of the raman effect

The system of coupled Stokes and Antistokes radiation interacting with two level molecules is analyzed for different degrees of molecular cooperation. The generation of Stokes radiation from three level molecules is also studied. In both examples the electromagnetic field and the molecular levels are quantized and an exact solution to the Schrödinger equation is presented. The results give an insight into the role molecular coherence effects play in both spontaneous and stimulated Raman scattering.     

Coherence of two-level systems and relaxation

The relaxation of a two-level system interacting with radiation is studied using the method of coherent states. A solution of the equation for the quasiprobability density function is presented in two extreme cases of high and low photon field temperatures. In the first case, the equation has the form of a purely diffusion equation, and from the point of view of a spin interpretation, defines Brownian motion of a magnetic moment on a spherical surface. The second case leads to an equation of the general Fokker-Planck type, in which both diffusion and a systematic term are present. The results of an investigation of spontaneous emission of a system containing a large number of particles, using the quasiclassical approximation, are presented. In this approximation, a Gaussian distribution with a variable variance, whose center moves along a classical trajectory, is obtained for the quasiprobability distribution.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 77–80, October, 1981.     

Quantum efficiency and signal bandwidth of thallium atomic line filters

We derive a new, simplified method for the computation of trapping effects in coupled three-level atomic systems. The linearity of the Holstein radiation trapping equation allows the reduction of the general rate equation to the solution of the basic two-level Holstein equation and to an algebraic eigenvalue problem. The method is applied to the numerical simulation of the quantum efficiency and the signal bandwidth of thallium atomic line filters. With a pumping scheme that achieves population inversion between the ground state and the metastable state, 90% quantum efficiency and 10 MHz signal bandwidth can be achieved, while in noninverting pumping schemes, even quite high pump intensities result in less than 60% quantum efficiency and 8 MHz signal bandwidth. A tradeoff between quantum efficiency, signal bandwidth and pump power is possible.     

Pfaffian Solutions and Resonant Interaction Properties of a Coupled BKP Lattice

In this paper, we give a coupled lattice equation with the help of Hirota operators, which comes from a special BKP lattice. Two-soliton and three-soliton solutions to the coupled system are constructed. Furthermore, resonant interaction of the two-soliton solution is analyzed in detail. Under some special resonant condition, it is shown that low soliton can propagate faster than high one. Finally, the N-soliton solution is presented in the Pfaffian form.     

Pfaffian Solutions and Resonant Interaction Properties of a Coupled BKP Lattice

In this paper, we give a coupled lattice equation with the help of Hirota operators, which comes from a special BKP lattice. Two-soliton and three-soliton solutions to the coupled system are constructed. Furthermore,resonant interaction of the two-soliton solution is analyzed in detail. Under some special resonant condition, it is shown that low soliton can propagate faster than high one. Finally, the N-soliton solution is presented in the Pfaffian form.