利用虚光子理论对轴沟道辐射的分析

 考虑电子的反冲的影响，利用虚光子与相对论电子的康普顿散射理论对轴沟道辐射进行了研究。在与电子纵向运动静止的坐标系中，把晶格场等效为虚光子。当虚光子与作沟道运动的电子发生康普顿散射时，虚光子就会转化为实光子辐射出去。根据该理论，得到了含有康普顿波长项的轴沟道辐射的精确波长表达式，其近似式就是经典理论推导的公式；同时得到了单电子轴沟道辐射的光子产额和辐射功率的公式，结果也与经典理论公式一致。     

利用虚光子散射对回旋脉塞自发辐射的分析

利用电磁场变换分析了带电粒子在磁场中的螺旋运动,基于康普顿散射理论和多普勒公式分析了虚光子与带电粒子的康普顿散射,并推导了在磁场中做螺旋运动的带电粒子的自发辐射波长公式.结果表明,当带电粒子在回旋脉塞的磁场中作螺旋运动时,在粒子静止系中可以观察到运动的周期性变化电场和磁场,即运动的虚光子.通过与带电粒子发生康普顿散射,虚光子能够转化为实光子辐射出去.     

SASE自由电子激光起振问题及统计特性的数值模拟

 介绍一种自放大自发辐射自由电子激光（SASE FEL）的自发辐射和电子束噪声的数学描述，运用修正的一维非定态程序，对SASE FEL 起振问题及光场统计特性进行了数值模拟，分析了自发辐射谱的发展过程及一定频带宽度内光场随机特性的统计规律，数值模拟结果与理论结果符合较好。     

CAEP远红外100 μm FEL自发辐射谱的实验研究

在FEL实验中,电子束通过摇摆器,一方面由于周期性磁场作用,电子束轨迹要周期性的摆动,另一方面还要辐射同FEL辐射波长一致的自发辐射,该辐射谱反映电子束、摇摆器集成后的参数。在CAEP(Institute of China Academic Engineering Physics)远红外100 μm FEL实验中,自发辐射谱通过Ge∶Ga低温探头和远红外100 μm光栅谱仪测量。文章侧重从实际摇摆器磁场分析了远红外100 μm FEL的自发辐射谱。     

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。     

Born近似散射幅的分波法推导

本文给出一种不同于通常教科书的推导散射振幅的Ｂｏｒｎ近似公式的方法．通过求解径向运动方程，我们得到了微扰的辏力场Ｕ（ｒ）产生的相移δｌ，再根据计算散射幅的分波法一般公式，并利用Ｇｅｇｅｎｂａｕｅｒ加法公式，推出了 Ｂｏｒｎ近似下的散射幅．     

无角度限制的修正的Glauber公式

本文重新推导了Glauber理论中弹性散射振幅公式。如果取直角光学位势作为零级近似,取Woods-Saxon光学位势作为正确的光学位势,发现在原来的散射振幅中,分部积分能够进一步进行下去。最后,得到了修正后的散射振幅公式,而无角度限制。 关键词：     

水下掩埋目标的散射声场计算与实验

水下掩埋目标声散射问题是识别和探测掩埋目标的理论基础, 是声散射研究领域的热点问题. 本文基于射线声学推导了掩埋情况下目标声散射计算的格林函数近似式, 并在此基础上进一步给出了相应的远场积分公式. 在有限元方法的基础上, 将推导得到的公式写入有限元仿真软件, 对软件功能进行拓展, 构建二维轴对称目标的声散射模型, 并计算掩埋情况下弹性实心球在不同条件下的目标强度, 获得了其散射声场随频率、掩埋深度、沙层吸收系数等参数的变化规律. 开展实心球的自由空间和浅掩埋条件下水池声散射实验, 利用共振隔离技术处理实验数据, 提取目标声散射的纯弹性共振特征进行分析, 结果表明可将其用于掩埋目标识别和探测. 最后利用总散射声场与理论计算结果进行对比, 验证了理论仿真的正确性.     

二维粗糙海面散射回波多普勒谱频移及展宽特征

基于二维线性海面模型及粗糙面电磁散射的一阶小斜率近似公式,研究了海面回波各阶多普勒谱的频移特性,得到了多普勒谱频移所对应的理论公式,与经典多普勒频移公式相比考虑到了风速、大尺度波浪轨道运动等因素对多普勒谱频移的影响;同时根据粗糙面的双尺度模型,基于多普勒谱频移的物理机理,给出了求解散射场多普勒谱展宽的理论公式.最后将理论公式计算所得结果与模拟结果及实测数据进行了比较,讨论了风速、入射波频率及入射角等因素对多普勒频移及多普勒谱展宽的影响.通过比较可以发现,给出的理论公式可以对多普勒谱频移和展宽进行一定程度的预测. 关键词： 粗糙海面 电磁散射 多普勒谱     

强激光大气传输中拉曼散射的数值计算

用经典理论推导了强激光大气传输中由于氮的转动受激Ｒａｎｍａｎ散射所造成的对传输功率的限制方程，并计算了光强的阈值，得到了阈光强与激光波长和脉宽的关系；此外，还研究了二维效应和激光脉冲系列通过大气时声子激发的累加效应。     

Classification of dark pion multiplets as dark matter candidates and collider phenomenology

In this work we propose to use leading singularities to obtain the classical pieces of amplitudes of two massive particles whose only interaction is gravitational. Leading singularities are generalizations of unitarity cuts. At one-loop we find that leading singularities obtained by multiple discontinuities in the t-channel contain all the classical information. As the main example, we show how to obtain a compact formula for the fully relativistic classical one-loop contribution to the scattering of two particles with different masses. The non-relativistic limit of the leading singularity agrees with known results in the post-Newtonian expansion. We also compute a variety of higher loop leading singularities including some all-loop families and study some of their properties.     

Improved Analytical Approximations to the Scattering Solutions of the Schrdinger Equation with a Hyperbolical Potential

Using an improved approximate formula to the centrifugal term, we present arbitrary l-state scattering solutions of the hyperbolic potential. The approximate analytical formula of scattering phase shifts and normalized wavefunctions are presented. All data calculated by the above approximate analytical formula are compared with those obtained by using the numerical integration method in the scattering state cases. We find that this improved approximate formula is better than previous one since the calculated results are in good agreement with those exact ones.     

Improved Analytical Approximations to the Scattering Solutions of the Schrödinger Equation with a Hyperbolical Potential

Using an improved approximate formula to the centrifugal term, we present arbitrary l-state scattering solutions of the hyperbolic potential. The approximate analytical formula of scattering phase shifts and normalized wavefunctions are presented. All data calculated by the above approximate analytical formula are compared with those obtained by using the numerical integration method in the scattering state cases. We find that this improved approximate formula is better than previous one since the calculated results are in good agreement with those exact ones.     

A quantum version of the inverse scattering transformation

We derive a formula that expresses the local spin and field operators of fundamental graded models in terms of the elements of the monodromy matrix. This formula may be understood as a quantum version of the classical inverse scattering transformation.     

Spectral properties of dissipative chaotic quantum maps

I examine spectral properties of a dissipative chaotic quantum map with the help of a recently discovered semiclassical trace formula. I show that in the presence of a small amount of dissipation the traces of any finite power of the propagator of the reduced density matrix, and traces of its classical counterpart, the Frobenius-Perron operator, are identical in the limit of variant Planck's over 2pi -->0. Numerically I find that even for finite variant Planck's over 2pi the agreement can be very good. This holds in particular if the classical phase space contains a strange attractor, as long as one stays clear of bifurcations. Traces of the quantum propagator for iterations of the map agree well with the corresponding traces of the Frobenius-Perron operator if the classical dynamics is dominated by a strong point attractor. (c) 1999 American Institute of Physics.     

Effect of finite terms on the truncation error of Mie series

The finite sum of the squares of the Mie coefficients is very useful for addressing problems of classical light scattering. An approximate formula available in the literature, and still in use today, has been developed to determine a priori the number of the most significant terms needed to evaluate the scattering cross section. Here, we obtain an improved formula, which includes the number of terms needed for determining the scattering cross section within a prescribed relative error. This is accomplished using extended precision computation for a wide range of commonly used size parameters and indices of refraction. The revised formula for the finite number of terms can be a promising and valuable approach for efficient modeling light scattering phenomena.     

Quantum chaotic scattering in atomic physics: Ericson fluctuations in photoionization

We report the first experimental investigation of quantum chaotic scattering in an atomic system: in strong crossed magnetic and electric fields in an energy regime beyond the ionization threshold, where the classical dynamics is an example of chaotic scattering. We find Ericson fluctuations in the spectra for photo excitation into this regime. This result constitutes the first observation of Ericson fluctuations in atomic and molecular physics. Furthermore, we confirm the prediction that chaotic scattering in the underlying classical dynamics implies Ericson fluctuations.     

Cascades of Fano resonances in Mie scattering

The interference nature of resonant Mie scattering, which is described within the Fano model, has been demonstrated. The interference is caused by interaction of an incident electromagnetic wave with reemitted waves that correspond to eigenmodes of a scattering particle. Mie scattering due to the interference can be represented in the form of cascades of resonance lines of different shapes, each of which is described by the classical Fano formula. The effect is observed in resonant light scattering by an arbitrary body of revolution and discussed in detail using the example of scattering by an infinite homogeneous dielectric cylinder.