微波单缝衍射实验中的畸变现象研究

介绍了微波单缝衍射实验中出现的畸变现象,研究了单缝宽度、挡板面积、单缝结构、发射喇叭与载物台间距对畸变现象的影响. 结合实验对畸变现象进行分析,通过增加单缝宽度和挡板面积、改变单缝结构及发射喇叭与载物台间距可以很好地消除畸变现象,得到与理论图样吻合很好的实验图样.     

简单实用的学生双缝干涉、单缝衍射观察筒

针对高二物理学生实验"观察双缝干涉现象"所用仪器--J2515型双缝干涉实验仪零部件多,组装调整麻烦,教师准备费时、费力,学生实验时很难掌握操作要领,不易观察到清晰的干涉图像等缺点,我们设计制作了简单实用的学生双缝干涉、单缝衍射观察筒,供分组实验用.多年实践证明,效果非常好,在2000年7月北京召开的首届全国教育工作者发明与科教制作的展评中被评为三等奖,现介绍如下.     

关于单缝衍射的疑点辨析

由惠更斯-菲涅尔原理可知衍射就是子波的干涉.虽然双缝干涉与单缝衍射同为干涉,但是它们的明暗条纹条件却存在很大差异.下面从物理角度对这一疑点给出清晰的定性解释,并且从数学角度给出单缝衍射明暗条纹产生条件的严格证明.     

微波单缝衍射的实验研究及数值模拟

对微波单缝衍射实验仪器和实验数据进行了分析,建立了微波分光计衍射理论模型,并对其进行了数值模拟计算,发现衍射曲线是单缝和发射源前的矩形喇叭口2次衍射叠加的结果,且与数值模拟计算结果吻合相当好.     

微波脉冲窄缝耦合的数值并行计算

采用时域有限差分方法（FDTD）对微波脉冲与窄缝耦合过程进行了数值模拟计算,分析了数值模拟计算过程中的并行性,给出了相应的并行算法,算法中采用消息合并和计算与通信重叠技术来减少通信阳,分析了算法的通信复杂性,给出了在Alpha工作站上的测试结果。     

从双缝实验看干涉和衍射的本质

以双缝为例,从装置图、实验照片和光强度分布入手,讨论了双缝干涉与双缝衍射的区别和联系,从而较深入地探讨了光波干涉与衍射的本质.     

易于数字化处理等离子体密度的微波干涉仪

一、引言 用微波干涉仪测量等离子体电子密度是一种常用的诊断手段,但通常不易于数字化,并且精度也不高。本文描述了用阶梯波调制的微波干涉仪原理,提出了用计算机直接处理干涉信号的方法,并实际测得了密度曲线。实验结果表明:这种干涉仪的原理及处理方法对于稳态长脉冲等离子体实验装置的密度测量是可行的。测量的相移量容易达到π/10。并且不需增加任何电子线路和微波器件。     

相位正态分布条件下的微波合成效率

针对多台高功率微波源组阵进行功率合成时相位离散分布的问题,基于数理统计方法对合成阵元相位误差呈正态分布情况下阵列合成效率进行了理论分析,提出了相位误差有界分布下其概率密度函数的表达式,修正了相位分布标准差较大时微波功率合成效率的理论计算公式。为验证修正后的理论公式正确性,使用数值模拟方法计算了合成阵列天线阵元激励信号相位误差呈正态分布下的空间功率合成效率,计算结果表明,数值模拟结果与理论分析给出的计算结果吻合得较好,修正后空间功率合成效率公式的预估精度得到有效提高。     

相位正态分布条件下的微波合成效率

针对多台高功率微波源组阵进行功率合成时相位离散分布的问题,基于数理统计方法对合成阵元相位误差呈正态分布情况下阵列合成效率进行了理论分析,提出了相位误差有界分布下其概率密度函数的表达式,修正了相位分布标准差较大时微波功率合成效率的理论计算公式。为验证修正后的理论公式正确性,使用数值模拟方法计算了合成阵列天线阵元激励信号相位误差呈正态分布下的空间功率合成效率,计算结果表明,数值模拟结果与理论分析给出的计算结果吻合得较好,修正后空间功率合成效率公式的预估精度得到有效提高。     

不同形状孔缝微波耦合的实验研究

探讨了椭圆、圆环、方环、十字交叉形、圆形、正方形、正三角形及双矩形孔缝在2～18GHz频率范围内的耦合系数，并与矩形孔缝的耦合特性进行了比较。结果表明: 各种不同形状孔缝微波耦合的共振特性与其纵横比有关, 纵横比较大的孔缝耦合共振现象比较明显，纵横比较小的孔缝耦合特性趋于高通；各种孔缝的共振频率与孔缝长度有密切关系。     

On factors affecting diffraction efficiency in thermoplastic hologram recording

Experimental results are presented concerning the dependence of diffraction efficiency in thermo-plastic recording on (a) development temperature and (b) thickness of the plastic layer. The data relate to the technique of simultaneous recording and development. The “factor of two” rule linking centre ferquency and thickness is shown to have little practical relevance.     

The influence of some geometrical and physical factors on the diffraction patterns of polycrystals

A method of grain size determination in polycrystals from the number of spots on Debye-Scherrer rings serves here as experimental basis for the study of the influence of a) parameters of the experimental arrangement (e.g., divergence of primary beam, choice of the standard blackening and ratio of exposures), and b) properties of the specimen (e.g., preferred orientation of grains and their local distribution of sizes), on the results of measurement. Sufficiently numerous statistical sets of experimental data show that the counting of spots may be quite exact, but the usually applied relation between the number of spots and grain size is likely appreciably oversimplified. As the assumptions, from which the mentioned relation was deduced, are closely connected with problems of X-ray diffraction, the results presented in this paper may be interesting from a more general point of view. The X-ray results are also compared to the metallographic ones.The possibility of grain size determination from counting spots on one diffraction photograph even in back reflexion region is pointed out in Appendix.Cukrovarnická 10, Praha 6, Czechoslovakia.The author is indebted to Dr. J. ermák C.Sc. for encouraging discussions and for steady interest during the work.     

Direct observation of double diffraction patterns

The double diffraction light intensity of two identical gratings placed parallel in the Fresnel region is sensitive to the lateral displacement ΔX, and is also affected by the air gap R between the gratings. In this note, the dependence of the double diffraction light intensity on ΔX and R for each order beam has been obtained directly by observing the intensity pattern on a screen.     

PAA-assisted synthesis of CaCO3 microcrystals and affecting factors under microwave irradiation

In the present paper, we described a polyacrylic acid (PAA)-assisted microwave irradiation route for synthesis of Calcium carbonate (CaCO₃) microcrystals. CaCl₂·2H₂O and NaHCO₃ were used as the starting reactants. Researches showed that the presence of PAA could strongly affect the phase and morphology of CaCO₃ crystals. X-ray powder diffraction (XRD) analyses showed that the product prepared from the system with/without PAA corresponded to Vaterite/Calcite, respectively. Scanning electron microscopy (SEM) observations showed that the hierarchical CaCO₃ microcrystals were obtained in the presence of PAA. Some factors influencing the morphology of the as-synthesized CaCO₃ crystals were systematically investigated.     

Anomalous diffraction effects observed on the x-ray diffraction patterns of decomposing supersaturated solid solutions

The basic purpose of an x-ray study of the initial stage of the decomposition of a supersaturated solid solution is to determine the shape, size, and relative orientation of the anomalous-scattering regions in the reciprocal lattice (in reciprocal space) from the anomalous diffraction effects observed on the diffraction patterns. From the size, shape, and relative orientation of the various anomalous-scattering regions in reciprocal space one can draw quite reliable conclusions regarding the nature of the same distortions in the matrix lattice, due to the observed anomalous diffraction effects. An analytic method is proposed for calculating the anomalous-scattering regions in reciprocal space for the most general case of an unknown crystal orientation.     

Experimental evidence of the phase reversal in diffraction patterns

In a diffracted wavefield occurs in patterns phase variations. The most familiar example is the Fraunhofer diffraction pattern through a single slit: the theory predicts that the side bands of the diffraction pattern alternate in phase. This paper deals with phase reversal phenomenon in diffraction patterns. Two interesting systems are recognized: the diffraction through a half plane and the diffraction through a single slit.     

Fractal analysis of powder X-ray diffraction patterns

X-ray diffraction (XRD) patterns with broad background are commonly found in the characterization of materials with a certain degree of amorphicity, so the sharp intensity peaks associated with material phases are not well defined. This work used rescaled range (denoted by R/S) analysis, a method intended for fractal analysis of noisy signals, to characterize XRD patterns with broad background. It is found that XRD patterns with broad background are not random at all, but contain information on regularities expressed as autocorrelations of the intensity signal. Sol-gel alumina fired at different temperatures was used as an example to illustrate the applicability of the method. It is shown that fractal R/S analysis is able to locate angular regions that can be associated to ideal International Centre for Diffraction Data Powder Diffraction File (ICDD PDF) lines of diverse alumina phases.     

The single crystal diffraction patterns of silicon

A triple-crystal diffractometer is used to study the single crystal diffraction patterns of Si (111), (220), (333) and good agreement with the dynamical theory of X-ray diffraction on perfect single crystals is found. This proves the possibility of using Si single crystals as in X-ray spectroscopy for a double-crystal spectrometer with a high resolving power as well as for studying very narrow diffraction patterns by means of a triple-crystal diffractometer.

---

Si

Si (111), (220), (333); . Si , .

---

---

The authors thank R. ida and F. Hájek for designing and making the automatic equipment for measuring the curves and V. Smutná and A. Irra for carefully performing the auxiliary work.     

Aberrated diffraction patterns of off-axis Gaussian beams

Fraunhofer diffraction patterns of off-axis Gaussian beams passing through an optical system having primary spherical aberration are investigated. The resultant diffraction patterns show a nearly elliptical form with a transverse focal shift which depends on the incident position of the Gaussian beams on the pupil and on their radius.