方孔夫琅禾费衍射的数值模拟

根据惠更斯-菲涅耳原理,利用数值计算的方法对方孔夫琅禾费衍射实验进行了模拟,在验证衍射理论的同时,还得到了非傍轴区域和微方孔的衍射图,拓展了衍射的概念,为深入理解光的衍射提供了参考.     

高斯光束照射下的圆盘夫琅禾费衍射

推导了高斯光束照射圆孔或圆盘的衍射场普遍表达式，计算了半波带数接近于零的情况下上述衍射场的数据，进而分析了圆盘衍射场在艾里斑中增加一个暗环的原因。     

菲涅耳衍射与夫琅禾费衍射公式对自由传播问题的自洽性

考察了菲涅耳衍射积分公式和夫琅禾费衍射积分公式在处理相继自由传播问题中的行为，证明了只要注意近似条件的正确运用，这些公式对自由传播问题可以给出自洽的结果；同时讨论了菲涅耳公式中当λz→0时的极限情况及其物理意义。这些分析对于加深对两个公式的物理意义、运用条件及有效性的理解是有益的。     

模拟分析光的衍射与干涉

基于物理光学的惠更斯-菲涅耳原理及基尔霍夫积分公式,应用Matlab软件编程模拟了光的单缝衍射和双缝衍射(干涉),从而形象地给出了衍射和干涉的内在区别和联系,也为相关的光学教学设计提供了新思路.     

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。     

用月牙形波带求圆孔夫琅禾费一级衍射环的角半径

用类似菲涅耳半波带的简单几何分析方法，近似导得了圆孔夫琅禾费衍射的中央明斑和一级明环的角半径。     

对称分布的相位型互补衍射屏的夫琅禾费衍射

为了验证巴比涅原理在相位型互补衍射屏的应用,建立了相位型互补衍射屏的数学模型,由理论分析得出了二者复振幅透过率的表达式,与用傅里叶光学方法得出其在频谱面上光强分布的表达式相同.由计算机模拟得到抛物柱面相位型互补衍射屏的夫琅禾费衍射光强的分布规律,与理论分析一致,得出分布规律为偶函数的相位型互补衍射屏的衍射符合巴比涅原理.     

倾斜因子对夫琅禾费衍射强度的影响

利用傅里叶光学详细讨论了斜入射情况下的夫琅禾费衍射,导出了大角度斜入射和衍射下的光强理论分布,分析了倾斜因子对衍射花样的影响.利用该理论对平行光斜入射光栅衍射实验的衍射花样进行了理论模拟,理论与实验基本相符.     

采用衍射掩模产生白光横向平顶光束

白光横向平顶光束在定向背光式自由立体显示器中有重要应用.本文提出一种采用带蝶形小孔阵列的衍射掩模片获得白光横向平顶光束的方法.根据广义惠更斯-菲涅耳衍射积分和多波长叠加原理,推导出光强分布计算式.设计一套实验装置,数值模拟并实验验证出射光束在不同距离的横向光强分布以及小孔蝶形凹度(蝶形中心高度与边长的比值)对横向光强分布的影响.结果表明:当选择小孔蝶形凹度为0.50—0.66时,可以得到平顶因子F 0.89的白光横向平顶光束,横向平顶光束的宽度随着传输距离的增大而增大,而平顶因子基本不变.实验还发现柱面透镜的折射色散和衍射色散可以互相抵消,使白光横向平顶光束基本无色散.     

字母屏的夫琅禾费衍射分析及计算机模拟

利用电寻址液晶光阀实验系统,通过将计算机绘制的英文字母A至Z输出到液晶屏上形成物屏,拍摄了其夫琅禾费衍射图样.在理论上进行了计算比较和分析,同时结合计算机Matlab等对光强分布进行了模拟,揭示了夫琅禾费衍射中物与像的内在联系.     

The rigorous electromagnetic theory of the diffraction of vector beams by a circular aperture

The rigorous electromagnetic theory of the diffraction of vector beams by an aperture is proposed and numerically evaluated by the diffraction of vector Gaussian beams by a circular aperture. The results are compared with those, by using the vector Rayleigh–Sommerfeld diffraction integrals and angular-spectrum expression theory, showing a good consistency. The numerical calculation shows that the result calculated by the rigorous theory is much more precise than those calculated by the integral method in diffraction near field, and a highly consistency reaches by the three methods in diffraction far field. A further extension of the theory is discussed.     

A different method for calculation of the deflection angle of light passing close to a massive object by Fermat’s principle

We introduce a method for calculating the amount of deflection angle of light passing close to a massive object. It is based on Fermat’s principle. The varying refractive index of medium around the massive object is obtained from the Buckingham pi-theorem.     

The interplay between the lattice and magnetism in La（Fe11.4Al1.6）C0.02 studied by powder neutron diffraction

The crystallographic structure and magnetic properties of La（Fell.4Alz.6）C0.02 are studied by magnetic measurernent and powder neutron diffraction with temperature and applied magnetic field. Rietveld refinement shows that La（Fe11.4Al1.6）C0.02 crystallizes into the cubic NaZn13-type with two different Fe sites： FeI （8b） and FeII （96i）, and that A1 atoms preferentially occupy the FeII site. A ferromagnetic state can he induced at a medial temperature of 39 K-139 K by an external magnetic field of 0.7 T, and a large lattice is correspondingly found at 100 K and 0.7 T. In all other conditions, La（Fe11.4Al1.6）C0.02 has no net magnetization in the paramagnetic （T 〉 TN = 182 K） or antifer- romagnetic states, and thus keeps its small lattice. Analysis of the Fe Fe bond length indicates that the ferromagnetic state prefers longer Fe-Fe distances.     

Simulation and experiments for the Q_(ext) of a cavity beam position monitor

The external Q (Q_(ext)) of the dipole mode is a key parameter of the Cavity Beam Position Monitor (CBPM).It determines the amplitude and length of the dipole mode signal.In this paper,Q_(ext) of a CBPM whose waveguides were open to the air was simulated and measured,and the results agreed with each other.Then four waveguide-to-coaxial cable adpaters were adjusted and assembled to the CBPM,and Q_(ext) remained unchanged.This progress provides a reliable method to evaluate Q_(ext) in the physics design without simulating the structurally complex adapters.     

The 2 × 1 reconstruction of the rutile TiO2(0 1 1) surface: A combined density functional theory, X-ray diffraction, and scanning tunneling microscopy study

An extensive search for possible structural models of the (2 × 1)-reconstructed rutile TiO₂(0 1 1) surface was carried out by means of density functional theory (DFT) calculations. A number of models were identified that have much lower surface energies than the previously-proposed ‘titanyl’ and ‘microfaceting’ models. These new structures were tested with surface X-ray diffraction (SXRD) and voltage-dependent STM measurements. The model that is (by far) energetically most stable shows also the best agreement with SXRD data. Calculated STM images agree with the experimental ones for appropriate tunneling conditions. In contrast to previously-proposed models, this structure is not of missing-row type; because of its similarity to the fully optimized brookite TiO₂(0 0 1) surface, we call it the ‘brookite (0 0 1)-like’ model. The new surface structure exhibits two different types of undercoordinated oxygen and titanium atoms, and is, in its stoichiometric form, predicted to be rather inert towards the adsorption of probe molecules.     

Studies on the ZrO/W(100) surface by means of low-energy electron diffraction and X-ray photoelectron spectroscopy

The low work-function ZrO/W(100) surface was examined with the aim of understanding the reducing mechanism of the work function. Low-energy electron diffraction (LEED) was employed to analyze the surface atomic arrangement, and X-ray photoelectron spectroscopy (XPS) was used to identify the surface chemical condition. The ZrO/W(100) surface was made as follows: (i) around three monolayers of Zr were deposited on a clean W(100) surface, (ii) the sample was heat treated in an oxygen ambience of 1.3x10⁻⁵ Pa for several tens of minutes at 1500 K, and (iii) the sample was flash heated at 2000 K in ultrahigh vacuum (UHV). During heat treatment in O₂, the deposited Zr was oxidized to ZrO₂, and the LEED pattern formed was p(2×1). The work function increased to 5.3 eV. Subsequent flash heating in UHV changed the p(2×1) LEED pattern into a c(4×2) pattern, and transformed ZrO₂ into the so-called Zr–O complex, the oxidized level of which is between ZrO₂ and metallic Zr. A drastic decrease in the work function to 2.7 eV ensued. The angular dependence of XPS showed that the Zr–O complex segregated within a few monolayers at the surface.     

The atomic geometries of the ordered (2 × 2) and (√3 × √3)R30° phases of K, Rb, and Cs on Rh(111) in comparison with Ru(0001)

The local adsorption geometries of K, Rb and Cs in the (√3 × √3)R30° and (2 × 2) phases on a Rh(111) surface at coverages of 0.33 and 0.25 ML, respectively, are determined by analyzing LEED intensity data. For all (√3 × √3)R30° phases investigated, the three-fold hcp site is found. For the (2 × 2) overlayer, K remains in the hcp position, while Cs favors the on-top position. For the case of Rb-(2 × 2), LEED analysis suggests occupation of the unusual two-fold bridge site. Since LEED analysis of the Rb-(2 × 2) phase is not completely conclusive, additional experimental evidence is necessary to firmly establish this adsorption geometry.     

Bi，Sb及稀土元素对AZ91镁合金高温性能影响机理研究

利用大角重位点阵概念建立了AZ91镁合金基体(α相)和镁［0001］对称倾斜晶界原子结构模型,应用实空间的连分数方法计算了体系的结构能,环境敏感镶嵌能以及相互作用能.结果发现,在镁合金基体中,Al和稀土形成团簇时比较稳定,Al,Bi或Sb与稀土形成团簇时不稳定.Bi或Sb和稀土元素同时存在于AZ91镁合金中时,一方面Bi或Sb将可与RE结合形成RE₂Bi(RE₂Sb)或RE-Bi(RE-Sb)化合物弥散分布于晶界,另一方面镁合金基体中会形成Al_{11关键词： 电子理论 晶界偏聚 合金元素 高温性能}