二元相位菲涅尔波带片近场俘获高低折射率粒子（英文）

采用双环形涡旋偏振光照射二元相位亚波长菲涅耳波带片的方法,实现了对高低折射率瑞利(Rayleigh)粒子的近场俘获.利用角谱理论计算了菲涅耳波带片的衍射场分布.改变入射光的截断参数(β)和涡旋角(δ),可以在菲涅耳波带片的近场区域产生亮斑和暗斑.计算发现,当β=1.09和δ=0时,在近场区域产生亚波长三维亮斑,能够稳定俘获19nm的金粒子,金粒子的折射率大于周围介质,轴向和横向俘获距离分别为0.4921λ和0.2844λ.当β=1.45和δ=0.414π时,在近场区域产生光墙包围着的三维暗斑,可以将30nm的空气泡稳定地俘获在暗斑中心,空气泡的折射率小于周围介质的折射率.两种情况计算所得的俘获距离均小于传统远场俘获系统中的距离.该系统可以用来精确俘获两类折射率不同的Rayleigh粒子.     

粒子场同轴全息图中对比度与再现像关系的讨论

本文以同轴全息中的比较典型的四种截面的粒子（－维线形、正方形、长方形圆形）为例,从理论上推导了这国种截面粒子的全息图对比度与远场数的关系,并做出对比度随远场数变化的曲线图。对照数值模拟得到的再现平面上的光强分布,分析照相系统对全息图的对比度的记录能力以及洗像过程对全息图信息的丢失程度的综合影响,以达到为优化照相条件和改善洗像工艺提供理论模型的目的。     

不同近远场外推方案对MRTD散射模型穆勒矩阵计算精度的影响分析

非球形气溶胶穆勒散射矩阵的不确定性是影响偏振遥感精度的重要因素。在自主研制的时域多分辨率(MRTD)气溶胶散射模型中,穆勒散射矩阵的计算需要以远场电场值为基础,因此近远场外推过程成为制约其模拟精度的重要环节。为确定适用于MRTD散射模型的最佳近远场外推方案,在球形和非球形粒子情形下,系统地对比分析了基于惠更斯原理的表面积分方案以及基于电介质亥姆霍兹方程的体积积分方案所对应的穆勒散射矩阵的模拟精度。结果表明,虽然两种近远场外推方案均可有效准确地实现近远场外推,但从穆勒矩阵的计算误差分布上看,基于体积积分原理的近远场外推方案性能更优。     

短波长激光在柱面条状虚共焦非稳腔中的传输

 用数值迭代方法求解了柱面条状虚共焦非稳腔的积分方程组。对相同及不同的菲涅耳数N-F和不同的放大率m等情况进行了数值计算。结果表明,在所取的N-F范围内近场光场强度的空间分布偏离均匀分布,但相位近似为均匀分布。其中小N-F和大m时不仅近场分布较为理想,而且远场强度的角分布接近衍射极限。     

圆形球面虚共焦非稳腔的三维数值研究

 通过对1/2共焦腔和稳定腔的计算,考查了同三维菲涅耳积分方程相应的C 8程序的可靠性。对激光在三维圆形球面虚共焦非稳腔中的传输作了计算和分析。取相同的远场传输距离且放大率由大变小时，强度分布由近场的投影分布逐渐趋于远场的高斯、超高斯分布。     

分形结构对随机取向烟尘团簇粒子光散射特性的影响

利用蒙特卡罗方法对不同分形维数和分形前向因子的随机取向烟尘团簇粒子的分形结构进行了仿真,采用离散偶极子近似（DDA）方法对随机取向烟尘团簇粒子的缪勒矩阵元进行了数值计算,并与球形粒子模型进行了比较,深入探讨了烟尘团簇粒子的分形维数和分形前因子对其散射特性的影响。研究表明,等效球形粒子的光散射特性与随机取向烟尘团簇粒子的光散射特性存在很大差别,并且此差别随着团簇粒子的分形维数以及分形前向因子的增大而减小;分形维数对表征团簇粒子散射特性的缪勒矩阵元的影响在一定散射角范围内均比较明显,分形前向因子对团簇粒子的缪勒矩阵元角分布的影响与分形维数的影响类似,不过其影响相对分形维数较弱。     

夫琅禾费衍射光强的反常分布和 Matlab模拟

讨论了夫琅禾费衍射实际实验中的反常现象,在一定条件下给出了计算机模拟的结果。实验表明,衍射图样的实验数据点分布结果与数值计算的模拟结果一致。由此可知,夫琅禾费衍射光强的反常分布是远场条件失效所致。     

数值法研究光的圆孔衍射实验现象

在平行平面波近似的情况下,数值法求解菲涅耳-基尔霍夫衍射积分公式,得到平行平面光波通过圆孔衍射后的光强分布图.通过对纵向及横向光强分布图的数值分析,验证了轴上点光强由菲涅耳数决定,菲涅耳数大于1时为菲涅耳衍射区,菲涅耳数小于1时为夫琅禾费衍射区.在近场,光强分布为明暗相间的环形条纹;在远场,光束演化成束腰位置在圆孔处的高斯光束,仿真结果与理论和实验结果基本一致.本仿真结果将光衍射的抽象理论直观化、可视化.     

涡旋洛伦兹-高斯光束的远场矢量结构特征

利用矢量角谱法和稳相法,研究了涡旋洛伦兹-高斯光束的远场矢量结构特征,导出了横电项(TE项)和横磁项(TM项)远场电磁场和相应能流的解析表达式。通过相应的数值计算,分析了拓扑电荷数对涡旋洛伦兹-高斯光束及其矢量结构项远场能流分布的影响。TE项由位于竖直方向的2瓣或3瓣组成,TM项可由TE项旋转90得到。涡旋洛伦兹-高斯光束在拓扑电荷数小时内部中空,外部亮环均匀分布。增大拓扑电荷数,涡旋洛伦兹-高斯光束外部亮环上的能流呈起伏分布,内部变化相对复杂。涡旋洛伦兹-高斯光束及其矢量结构项的光斑尺寸随拓扑电荷数的增大而增大,但会饱和。研究显示,涡旋洛伦兹-高斯光束在实际应用时拓扑电荷数不宜过大。     

菲涅尔区修正圆柱面天线的辐射特性

在圆柱面上进行一维菲涅尔区相位修正结构设计，可以构成一类新型的点源馈电透镜天线。本文利用矢量场绕射理论研究菲涅尔区修正圆柱面天线的辐射特性，并进一步分析馈源阵列作用下的辐射性能。文中天线远场方向图的计算结果与有关文献中的结果吻合。     

Quaternary fission

Quaternary fission is a nuclear reaction where the two customary fragments from fission are accompanied by two light charged particles. The process has been investigated at the ILL, Grenoble, for thermal neutron induced fission of ²³³U and ²³⁵U. The light particles were identified to be α particles and H isotopes (mostly tritons). Two different types of processes could be disentangled: in one of these processes all four charged particles are born in coincidence while the second process is in fact merely a special case of ternary fission where the ternary particle decays into two charged particles before reaching the detectors.     

Simulation of random mixed packing of different density particles

This paper presents the effects of density difference on the three-dimensional (3D) distribution of random mixed packing. The random mixed packing dynamics of particles of two different densities are simulated. The initial state is homogeneous, but the final packing state is inhomogeneous. The segregation phenomenon (inhomogeneous distribution) is also observed. In the final state, the top layers are composed of mostly light particles. The several layers beneath the top contain more heavy particles than light particles. At the bottom, they also contain more heavy particles than light particles. Furthermore, at both the top and the bottom, particle clustering is observed. The current study also analyses the cause of this inhomogeneity in detail. The main cause of this phenomenon is the velocity difference after collision of these two types of particles induced by the density difference. The present study reveals that even if particles were perfectly mixed, the packing process would lead to the final inhomogeneous mixture. It suggests that special treatment may be required to get the true homogeneous packing.     

New mechanism for the production of extremely fast light particles in heavy-ion collisions in the fermi energy domain

Employing a four-body classical model, various mechanisms responsible for the production of fast light particles in heavy-ion collisions at low and intermediate energies have been studied. It has been shown that, at energies lower than 50 A MeV, light particles of velocities of more than two times the projectile velocities are produced due to the acceleration of the target light particles by the mean field of the incident nucleus. It has also been shown that precision experimental reaction research in normal and inverse kinematics is likely to provide vital information about which mechanism is dominant in the production of fast light particles.     

A simple variation of the Marzke-Wheeler clock

The Marzke-Wheeler clock is based on the back-and-forth passage of a light signal between two observers who remain at rest with respect to one another. It differs from earlier photon clocks by providing a specific method based on the properties of free particles and light signals for establishing the relative rest of the two observers. The present paper provides an alternative and more straightforward method also based on the properties of free particles and light signals for accomplishing this result.     

Enhanced broadband light absorption in silicon film by large-size lumpy silver particles

Broadband light absorption enhancement in crystalline silicon thin-film solar cells by rear-located 400 nm lumpy silver particles has been studied, based on the theoretical simulations of 3D finite-difference time-domain method. By simulations, we have investigated the light scattering properties of 400 nm lumpy Ag particles and put it to silicon thin-film solar cells. In addition, the varying rear-located Ag particles coverage and two surface situations of silicon films, which could influence on the light absorption of solar devices, have also been comprehensively considered. The results have shown that rear-located 400 nm lumpy Ag particles would enhance the absorption in silicon films in a broadband range. And it has been proved that 20 % coverage density of rear-located Ag particles is optimal for improving the light absorption of smooth silicon thin-film solar devices. When we create rough surface on one or both sides of silicon films, the absorbed light would further increase, and the theoretical maximum enhancement is 15.1 % compared with the smooth silicon thin-film solar cell without Ag particles.     

Unusually strong optical interactions between particles in quasi-one-dimensional geometries

A theoretical analysis of the optically induced interaction between small particles in a quasi-one-dimensional system is presented. The total reflection of light modes near a geometric resonance leads to strong radiation pressure on a single particle. The presence of the two particles splits the resonance leading to a nontrivial oscillating interaction. The existence of stable, optically bound dimers under two counterpropagating (noncorrelated) light modes is also discussed.     

Orbits in the field of a gravitating magnetic monopole

Orbits of test particles and light rays are an important tool to study the properties of space-time metrics. Here we systematically study the properties of the gravitational field of a globally regular magnetic monopole in terms of the geodesics of test particles and light. The gravitational field depends on two dimensionless parameters, defined as ratios of the characteristic mass scales present. For critical values of these parameters the resulting metric coefficients develop a singular behavior, which has profound influence on the properties of the resulting space-time and which is clearly reflected in the orbits of the test particles and light rays.     

The spectral profile of light scattered by particles in electrophoretic movement

The electrophoretic movements of polystyrene latex particles suspended in water and in electrolyte solutions have been investigated with an optical beating technique. When two kinds of particles in water move in the presence of an external electric field, it is observed that the laser light scattered by these particles exhibits a shifted spectrum with a single peak profile, even if the electrophoretic mobilities of the two kinds of particles are different to each other. However, when these particles are suspended in an electrolyte solution, two separate spectral lines are observed which correspond to the velocity of each kind of particles.     

超短激光照射下颗粒的散射效应

对两个纳米颗粒受超短激光照射时表面吸收光强的分布情况进行了研究。基于米散射理论和蒙特卡罗方法建立程序来模拟和追踪光子的运动轨迹,米散射理论主要用于确定光子的散射方向,运用兰贝特定律和解析解对模拟结果进行验证。通过对比材料为金和黑体时双颗粒的光强分布发现,颗粒的散射和激光照射宽度的增加会使颗粒相邻处的光强增大,颗粒底部的光强主要取决于颗粒的反照率大小以及散射光强的分布情况。     

Some formulations of light scattering in laser flowmeters employing differential Doppler heterodyning

The theory for the Doppler shifted light is developed by diffraction theory combined with galilean transformation. The theory developed is applied to a differential Doppler heterodyning technique in which two beams are brought simultaneously, but at different angles, into the same area, and the cross region made by the two beams becomes a probing volume. When the concentration of scattering particles is so low that only one particle is found in the probing volume, the theory can be classified into two cases of a single particle and many particles depending on the analysing time for the Fourier transform, i.e. whether the time, during which one particle passes through the probing volume, is longer than the observing time or not. When the concentration of particles in the probing volume becomes dense, the light scattered by the different particles interferes and the theory shows great complexity. The cases of two particles and many particles showing a very high density are studied. Comparisons are made for the difference between differential Doppler heterodyning and normal heterodyning techniques.