Compton散射下等离子体球太赫兹散射特性

为了研究Compton散射对等离子体球太赫兹(THz)散射特性的影响,将多光子非线性Compton散射模型引入到该研究中,提出了将Compton散射作为影响等离子体球太赫兹散射的重要因素,给出了各向异性等离子体球散射场修正方程及介电常数张量、观测方位、极化状态等因素对THz波散射的影响,并进行了仿真实验。结果表明:微分散射截面随THz波频率变化近乎呈准谐振规律变化,较散射前增大了0.001;微分散射截面随观测方位和极化状态的变化较散射前增大了0.002。     

三能级钾原子气体三维傅里叶变换频谱的解析解

利用投影切片定理、傅里叶位移定理和误差函数给出三能级钾原子气体三维傅里叶变换频谱在T=0界面的解析解.固定均匀线宽,非均匀展宽和对角线相关系数可以定量地识别,通过在适当方向上拟合三维傅里叶变换频谱谱峰的切片来确定.结果表明,非均匀展宽增大,频谱图沿着对角线方向延伸,对角线相关系数增大,频谱图逐渐变圆,振幅也逐渐变小.     

一类非线性抛物型变分不等方程的全局吸引子及弱近似惯性流形

对由一类非线性抛物型变分不等方程所描述的无穷维动力系统，给出了存在全局吸引子及弱近似惯性流形的充分条件．     

部分相干电磁光束在湍流介质中传输的偏振变化

 从推广的惠更斯-菲涅尔原理出发，推导出了部分相干电磁光束的偏振态在湍流介质中传输的表达式。并以电磁高斯-谢尔模型(EGSM)光束为例，研究了湍流对电磁高斯-谢尔模型光束偏振态的影响。研究结果表明，对于轴上点，湍流介质的折射率结构常数越大，偏振度趋于最大值的速度越快，达到的最大值越小；光斑越大，偏振度达到最大值的位置离光源越远，在光斑增大的过程中，偏振度所达到的极大值会先增大后减小，最后保持与光源相同的偏振度不变。对于轴外点，一个固定的z，光的偏振度随着离轴距离的增大而逐渐下降，并最终等于零。折射率结构常数越大，偏振度随离轴距离的增大而下降得越缓慢；光斑越大，偏振度随离轴距离的增大下降得越快。     

匀速运动的电偶极子的电场和磁场分布

本文通过对电偶极子电磁势的分析和相对论下电磁场在不同惯性系中的协变分布，计算了作匀速直线运动的电偶极子的电场和磁场的空间分布．     

Second-order random wave solutions for interfacial internal waves in N-layer density-stratified fluid

This paper studies the random internal wave equations describing the density interface displacements and the velocity potentials of N-layer stratified fluid contained between two rigid walls at the top and bottom. The density interface displacements and the velocity potentials were solved to the second-order by an expansion approach used by Longuet-Higgins （1963） and Dean （1979） in the study of random surface waves and by Song （2004） in the study of second- order random wave solutions for internal waves in a two-layer fluid. The obtained results indicate that the first-order solutions are a linear superposition of many wave components with different amplitudes, wave numbers and frequencies, and that the amplitudes of first-order wave components with the same wave numbers and frequencies between the adjacent density interfaces are modulated by each other. They also show that the second-order solutions consist of two parts： the first one is the first-order solutions, and the second one is the solutions of the second-order asymptotic equations, which describe the second-order nonlinear modification and the second-order wave-wave interactions not only among the wave components on same density interfaces but also among the wave components between the adjacent density interfaces. Both the first-order and second-order solutions depend on the density and depth of each layer. It is also deduced that the results of the present work include those derived by Song （2004） for second-order random wave solutions for internal waves in a two-layer fluid as a particular case.     

High index of refraction via quantum interference in a three-level system of Er^3＋-doped yttrium aluminium garnet crystal

A simple three-level system is proposed to produce high index of refraction with zero absorption in an Er^3＋-doped yttrium aluminium garnet （YAG） crystal, which is achieved for a probe field between the excited state 4I13/2 and ground state 4I15/2 by adjusting a strong coherent driving field between the upper excited state 4I11/2 and 4I15/2. It is found that the changes of the frequency of the coherent driving field and the concentration of Er^3＋ ions in the YAG crystal can maximize the index of refraction accompanied by vanishing absorption. This result could be useful for the dispersion compensation in fibre communication, laser particle acceleration, high precision magnetometry and so on.     

Attractors for a Three-Dimensional Thermo-Mechanical Model of Shape Memory Alloys

Abstract In this note, we consider a Frémond model of shape memory alloys. Let us imagine a piece of a shape memory alloy which is fixed on one part of its boundary, and assume that forcing terms, e.g., heat sources and external stress on the remaining part of its boundary, converge to some time-independent functions, in appropriate senses, as time goes to infinity. Under the above assumption, we shall discuss the asymptotic stability for the dynamical system from the viewpoint of the global attractor. More precisely, we generalize the paper [12] dealing with the one-dimensional case. First, we show the existence of the global attractor for the limiting autonomous dynamical system; then we characterize the asymptotic stability for the non-autonomous case by the limiting global attractor. * Project supported by the MIUR-COFIN 2004 research program on “Mathematical Modelling and Analysis of Free Boundary Problems”.     

355nm Nd∶YAG激光在H_2中的高效一级斯托克斯转换

对脉冲Nd∶YAG激光(355 nm)在H2和H2∶He-Ar混合气体中的受激拉曼散射(SRS)进行了研究。在0.5 MPa的氢气中,同时测量到从二级反斯托克斯到三级斯托克斯的多波长输出,其总转化效率达88%;而高压下只剩下一级和二级斯托克斯输出,其中二级斯托克斯最大能量转化效率达44%(对应量子效率为63%)。由于高级斯托克斯的竞争,纯氢气中一级斯托克斯的最大能量转换效率不超过43%。通过向3 MPa氢气中掺入2 MPaAr气后,很好地抑制了二级斯托克斯的产生,从而获得了能量转换效率高达71%(对应量子效率为83%)的一级斯托克斯输出。对四波混频和级联受激拉曼散射在氢气多级斯托克斯产生中的作用以及惰性气体对它们的影响进行了讨论。     

The Quantum Coherence Effects in Degenerate Two-level Atomic System

The quantum coherence effects of the transition Fe = 2←→Fg = 3 depending on the polarization of the coupling and probe beam are observed in a Cs vapor cell. The splitting of electromagnetically induced transparency （EIT） window is observed when the degeneracy of two-level system is broken using a magnetic field. It is also shown that the splitted transparency points of two of three windows are shifted with the intensity of magnetic field （ i. e. Zeeman splitting in the upper and lower levels ） increasing. On the contrary, when we fix the intensity of magnetic field, and increase the Rabi frequency of the coupling beam, the splitted transparency peaks become wider. A qualitative agreement between experiment and theory is found.