Spectral shifts and spectral switches of a pulsed Gaussian beam from a rectangular aperture in the far field

The far-field anomalous spectral behaviours of a space–time-dependent Gaussian pulsed beam passing through a rectangular aperture are studied. By expanding a hard aperture function into a finite sum of complex Gaussian functions and starting from the Fresnel diffraction integral, the approximate analytical expression for the spectral intensity of a space–time-dependent Gaussian pulsed beam passing through a rectangular aperture is derived. Meanwhile, the corresponding closed-forms for the slit and the unapertured cases are also given as special cases of the general results. The red and blue shifts and the spectral intensity distribution are studied and illustrated with numerical calculations. Specifically, it is shown that the spectral switch takes place when the truncation parameter is equal to particular values or the observation position is at the critical diffraction angle. The possibility of tunable spectral switching in the far field with an apertured pulsed beam by varying the size of the rectangular aperture is highlighted.     

The effect of central obstruction on singularities and spectral anomalies of polychromatic,spatially coherent light diffracted by an annular aperture

The singularity changes and spectral behavior of polychromatic spatially fully coherent light diffracted by an annular aperture are studied. Detailed numerical calculation results are presented and illustrated. It is shown that the spectral anomalies take place in the vicinity of singularities in the diffraction field, namely the spectrum is red shifted at some points, blue shifted at others, and is split into two lines with equal height elsewhere, and this kind of spectral change depends on the central obstruction ratio ε and axial distance z. It is found that, with the increasing of the central obstruction ratio ε, axial singularities will shift to the aperture and at the off-axial positions new singularities will appear and split. With the further increasing of ε, the near field finally changes to the far field.     

Light intensity distributions of the Gaussian laser beam through an aperture team

Based on the propagating theory of the laser beam, the propagating characteristics of the Gaussian beam through an aperture team that comprises two apertures and a convergent lens, are studied. The approximate expressions for the field distribution are derived by the diffracted integral equation in detail under the condition of approximations. In comparison with the approximate expression and the precise expression, we know that there are the approximate same results for the two expressions if the radius of the second aperture is not too large. The numerical examples are given to confirm the correctness of our calculated results.     

Transformation of the V-dipole by an astigmatic lens

The transformation of the V-dipole by an astigmatic lens is studied analytically and numerically. It is found that after passing through the lens, the V-dipole splits into four C-points which make up two C-dipoles with same singularity index and opposite handedness. By a suitable choice of the astigmatic coefficient, off-axis distance, or propagation distance, the creation and annihilation of more than two C-dipoles may take place, as well as C-points may occur at the focal plane of the astigmatic lens. As a special case, only two C-dipoles annihilate or recreate and no polarization singularities appear at the focal plane in the presence of an ideal lens.     

Propagation of the Lissajous singularity dipole through an astigmatic lens

The propagation was investigated of a pair of Lissajous singularities of opposite singularity index called the Lissajous singularity dipole (LSD) through an astigmatic lens. It is shown that after passing through the lens the positions of the singularities are inverted and more than two LSDs occur. Changes in the degree of polarization of the LSDs as well as in the shape of the Lissajous figures also occur. In addition, Lissajous singularities may take place at the focal plane, and a single Lissajous singularity may appear and vanish under certain conditions. The results are compared with those of previous work.     

Observation of self-diffraction effect in acid blue 7 dye soaked gelatin films

Abstract

Permanent self-diffraction gratings are formed in red sensitive Acid blue 7 dye soaked gelatin films under illumination of an interference pattern by two linearly polarized beams from a He-Ne laser at 632.8 nm. Growth of the self-diffraction grating is monitored by measuring intensities of various diffraction orders. Systematic studies are carried out to investigate the influence of various parameters involved in diffraction efficiency of the grating such as time of exposure, concentration of dye in the gelatin-coated plate, intensity of interfering beams and intensity ratio of interfering beams. Efficient gratings with ten diffracted orders are formed. Several interesting observations are made by blocking one of the writing beams and an attempt is made to analyse these results.     

Resolution trade‐off analysis for aperture size and signaling bandwidth of diffraction tomography based on spatial‐frequency spectral coverage

The objective of this article is to present the trade‐off analysis of resolving capability of diffraction tomography between aperture size and illumination signal bandwidth based on the span of spatial spectral coverage. The analysis is conducted on both the transmission and reflection modes, and can be generalized into various data acquisition configurations. In addition, the analysis provides an important link to other tomographic imaging modalities such as the classical X‐ray tomography and synthetic aperture radar systems. © 2009 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 19, 1–4, 2009     

掺锶羟磷灰石固溶体陶瓷不同孔径对成骨能力的影响

通过控制发泡剂粒径的方法制得两组孔隙率相同孔径尺寸不同的掺锶羟磷灰石多孔体陶瓷:S组平均孔径200μm;L组平均孔径750μm.植入兔桡骨缺损部位,植入后3、6和12周取材,行X线观察、大体标本观察、组织学图像观察和四环素荧光染色观察,来对比不同孔径的锶磷灰石陶瓷多孔体的骨融合能力.结果表明锶磷灰石陶瓷多孔体具有良好的生物相容性及骨传导性;两种孔径材料都有良好的成骨性能,大孔径组锶磷灰石陶瓷多孔体材料比小孔径组材料有更佳的骨修复效果;且大孔径组在12周就能观察到陶瓷材料的降解以及新生骨包绕降解陶瓷颗粒生长的现象.     

泰伯-莫尔法测量长焦距系统的焦距

焦距是透镜最重要的光学参数，应用泰伯-莫尔法测量长焦距透镜焦距具有重要的实践价值。本文介绍了泰伯-莫尔法的原理，详细分析了各种实验方法，进行分类比较，并提出了改进措施。     

带凹槽平板型声透镜聚焦性能的理论分析与数值模拟

基于相位补偿和惠更斯-菲涅尔原理,利用理论分析和数值模拟的方法,研究了一种带凹槽的平板型声透镜,讨论了凹槽个数、声透镜材料等参数对声透镜聚焦性能的影响。结果表明:优化后的菲涅尔声透镜聚声效率理论上可达40%,放大倍数约为7倍,是一种较为高效、成本低廉的新型声透镜。     

大口径反射镜侧支撑结构力学分析

从理论上论述了在真空望远镜主反射镜的几种侧支撑结构,并运用有限元法对之分别进行了分析计算,得到使用了不同侧支撑结构的真空望远镜主镜在不同观测角度时的表面变形结果,通过比较变形结果,得到使用新配方粘接剂的粘接侧支撑机构支撑效果更好.在已确定使用Grubb十八点底支撑结构后,分析了使用粘接剂的侧支撑结构主反射镜变形与应力情况.通过有限元分析结果,得出变形结果符合整个光学系统的公差要求,同时证明了使用改性粘接剂的侧支撑系统可有效减少光学件表面变形量.     

Motion estimation in wide band synthetic aperture sonar based on the raw echo data using the method of displaced phase center antenna

Phase errors in synthetic aperture sonar (SAS) imaging must be reduced to less than one eighth of a wavelength so as to avoid image destruction. Most of the phase errors occur as a result of platform motion errors, for example, sway yaw and surge that are the most important error sources. The phase error of a wide band synthetic aperture sonar is modeled and solutions to sway yaw and surge motion estimation based on the raw sonar echo data with a Displaced Phase Center Antenna (DPCA) method are proposed and their implementations are detailed in this paper. It is shown that the sway estimates can be obtained from the correlation lag and phase difference between the returns at coincident phase centers. An estimate of yaw is also possible if such a technique is applied to more than one overlapping phase center positions. Surge estimates can be obtained by identifying pairs of phase centers with a maximum correlation coefficient. The method works only if the platform velocity is low enough such that a number of phase centers from adjacent pings overlap.     

蛋白质在水凝胶角膜接触镜上的吸附及对膜渗透性能的影响

以牛血清白蛋白(BSA)为模型蛋白,通过紫外分光光度法测定了BSA在共聚物水凝胶膜材料上的吸附量．研究了泪液中蛋白质在甲基丙烯酸-β-羟乙酯和N-乙烯基吡咯烷酮(HEMA—NVP)亲水性共聚物水凝胶的吸附情况．结果表明,蛋白质的吸附量随着吸附时间的增长而增大,4天基本达到吸附平衡．蛋白质在水凝胶上的吸附量随着水凝胶的平衡含水量增大而增大,吸附的蛋白质降低了水凝胶的离子通透性和透氧性．     

基于循环谱的同信道多信号调制方式识别

为满足软件无线电、认知无线电的需要,对共信道多信号的调制方式识别技术进行了研究,提出了一种共信道多信号调制方式识别的数学模型.根据此模型,结合循环谱理论,给出了基于循环谱的同信道多信号调制方式识别算法,并以BPSK、QPSK、OQPSK三种调制方式为例,采用蒙特卡洛方法对提出的算法进行了仿真.仿真和试验结果表明,提出的算法能有效地识别共信道多信号的调制方式,取得了与理论分析相吻合的结果.     

The effect of magnetic quadrupole lens hysteresis on the focusing of an ion beam with variable energy in a nuclear scanning microprobe

The influence of the hysteresis of magnetic quadrupole lenses on the transverse size of a beam focused on the target in a probe-forming system with a separated Russian quadruplet configuration has been experimentally studied. The measurements were performed in a nuclear scanning microprobe using a proton beam with the ion energy varied within 0.8–1.6 MeV. The beam size was determined by processing the secondary electron emission profiles measured during scanning of a calibrated micrometric square mesh. A new approach is proposed that allows a beam with variable energy in the nuclear microprobe to be focused so as to keep the probe size within preset limits.     

Experimental study of the effect of external signal on microwave oscillations in a nonrelativistic electron beam with virtual cathode

The effect of an external harmonic signal on the characteristics of microwave generation in a non-relativistic electron beam with virtual cathode (VC) formed in a static retarding electric field (low-voltage vircator system) has been experimentally studied. A significant increase in the vircator generation power is observed when the frequency of the external signal is close to the frequency of VC oscillations. At large detunings, a broadband chaotic generation is observed.     

海底与陆地地震动反应谱比定量分析

为了研究海底地震动与陆地地震动反应谱统计特性的差异,选取日本相模湾地区K-net的922组海底地震动记录和KiK-net的4 599组陆地地震动记录,通过对海底与陆地地震动标准化弹性加速度反应谱以及弹塑性反应谱的对比分析表明:弹性反应谱的海陆谱比变异较小,平均值可作为定量对比关系;当周期小于0.5 s时海域与陆地地震动...     

结温对高显指低色温白光LED光谱特性的影响

将MEH-PPV混合入YAG荧光粉中,并利用实验室自主研发的一种集成封装LED散热支架替代传统支架,该支架可利用热电偶直接测量出结温。研究了结温对混合MEH-PPV的白光LED光谱特性的影响。实验表明,随着结温的不断升高,蓝光光谱峰值随着结温的升高而不断下降,发生红移;荧光粉的吸收增强,黄光波段和红光波段的光谱峰值先增后减,并且红光波段的光谱发生蓝移;器件的显色指数从90.3下降至78.6,色温从3265K先快速升高至3672K,随后又缓慢下降至3612K,而光通量和发光效率则表现为先上升后下降,且它们的下降趋势基本吻合。     

Theoretical study on the spectral shifts of partially coherent array beams passing through ABCD optical systems

According to the extended Huygens–Fresnel integral, the expressions for the on-axis spectrum of partially coherent Gaussian Schell-model (GSM) rectangular array beams passing through ABCD optical systems have been derived. The generalized Fresnel number of the system, the spatial coherent parameter of array beamlets and the array beam parameters including the number of beamlets and the separation distance between beamlets have been taken as the characteristic parameters to compare the spectral shifts of GSM array beams for the two types of the superposition, i.e. the correlated superposition and the uncorrelated superposition. In particular, the effect of characteristic parameters on the on-axis relative spectral shifts has been discussed in detail. The results show that the spectral intensity of GSM array beams for the two types of the superposition passing through ABCD systems depends on the source spectral density S ⁰(ω), the spatial coherent parameter of array beamlets β, the generalized Fresnel number of the system F and the array beam parameters. Furthermore, for the uncorrelated superposition, the spectrum of GSM array beams only exhibit the blue-shift, whereas for the correlated superposition, GSM array beams exhibit the spectral switch and the number of spectral switches increases with the increase of array beam parameters in the near field due to the interference between beamlets. In particular, the effect of the array beam parameters on the on-axis relative spectral shift is more obvious.