A line-focus electron beam lens

A lens system has been developed to transform the circular beam from a conventional electron gun into a line-focus beam. The line-focus beam is uniform throughout its projected length on a phosphor screen.     

非对称磁透镜物镜的数字计算

采用数字化电子光学设计软件计算了扫描电子显微镜(SEM)物镜的光学特性并能在满足给定的条件下优化物镜设计。本文通过采用已发表的通用数据和用软件计算实际透镜得到的数据来计算电子束斑直径，研究非对称透镜物镜的光学特性。德国Tuebingen大学应用物理研究所的一个扫描电子显微镜电子光学系统采用了本文的计算结果。     

Aperture lens formula corrected for space charge in the electron stream

The aperture lens formula of Davisson and Calbick is rederived to include the effect of space charge forces. The correction is applied to a parallel flow Pierce gun, leading to the focal length reduction as a function of perveance, e.g., 30 per cent reduction at perveance 3 × 10^-6.     

电离层斜向传播模式的智能识别

采用数值统计与数字图像处理中形态学算子相结合的方法获得了高质量斜向探测电离图.结合观测描迹统计特性,利用改进的初始局部最大值和约束条件外推方法,实现了斜向探测电离层传播模式的智能识别,利用该方法可以自动提取常规电离图各传播模式对应的频率、群时延及信号能量等信息.     

The dispersion characteristics of oblique coordinate beampropagation algorithms

The use of an oblique coordinate system with the finite difference beam propagation method has previously been demonstrated to offer significant computational advantages over using rectangular coordinates for a wide range of practical optical structures. The effects of finite mesh resolution, step size, and order of the algorithm in terms of numerical dispersion and dissipation are here investigated and quantified for the first time     

AMRAY-1000B扫描电镜透镜系统

AMRAY-1000B扫描电镜透镜系统的工作参数已由厂家存储在编程ROM中.透镜电流的变化由计算机控制,计算机接受面板操作指令.具体是:面板操作→计算机响应→调数据→数据缓冲器→数模转换(D/A)→激励功放与反馈→透镜线圈.下面对该系统的电路、故障检测方法与步骤进行分析和讨论.     

The integral lens coupled LED

A new technique is described which enables increased coupling efficiencies to be obtained between N-side emitting, high radiance, double heterostructure (GaAs/GaAlAs) LED’s and multimode glass fibers. The technique consists of creating by means of photolithographically defined etching and epitaxial regrowth, a large number of converging micro lens structures in the emitting surface of the semiconductor. Lensed LED’s have been fabricated which exhibit an effective brightness of 75 W/sr-cm² at a current density of 3.4 KA/cm² . The new devices represent an improvement in certain applications of 40 to 100% over similar non-lensed structures.     

斜测电离图描迹的自动提取

提出了一种能同时获取斜测电离图描迹和参数的方法,该方法采用准抛物模型描述电离层 F2层电子浓度分布。利用正割定理、Martyn 等效虚高定理、图像处理技术和电离图的回波特征确定部分电离层状态参数的最终值和部分参数的初始值及搜索空间。然后,利用最小群时延和残差分析提取 Es 层描迹。最后,使用混合遗传算法从搜索空间范围内找出一组最优参数,使合成的斜测电离图 F2层描迹与真实描迹吻合得最好。为了验证自动提取方法的有效性,对240张斜测电离图进行了自动提取,将得到的结果与斜测电离图的人工提取结果进行比较,结果显示该方法能够较准确地提取斜测电离图描迹和参数。     

The scanning electron microscope

The scanning electron microscope combines the techniques of the cathode-ray tube and the conventional electron microscope?both considered indispensable to modern technology. The SEM, which presents a picture having a distinct three-dimensional appearance, is finding application in the examination of wood fibers in connection with paper manufacture, of surfaces undergoing ionic bombardment, and of corrosion. At the present time, one of the most pressing problems is to reduce its total cost.     

The multipactor electron gun

An electron source based on the multipactoring principle and preliminary experimental results are described. Several uses of such a gun are suggested.     

折衍混合在长焦物镜中的应用研究

为了突破长焦物镜传统设计中的局限性,从衍射面的相位多项式出发,结合一般透镜的相位变换式,对折衍混合消像差理论进行了探讨。给出了仅使用1种材料FK1、2片型的长焦物镜系统设计结构,并将此设计结果与传统的5片型、5种材料的纯折射长焦物镜的光学性能进行了比较。结果表明,利用折衍混合能有效地校正长焦物镜的像差,极大地降低系统的重量和复杂程度,不失为长焦物镜设计的一条有效途径。     

The scattering and absorption characteristics of material-coatedperiodic gratings under oblique incidence

A boundary integral formulation is presented for calculating the scattering from material-coated periodic gratings under oblique incidence. Periodic boundary conditions and expansion of the fields in terms of Floquet harmonics allow the boundary integral formulation to treat just a single period of the infinite grating. Numerical results for an etched conducting grating designed for use at infrared wavelengths are presented and shown to be in good agreement with a series of measurements. Results for a number of dielectric gratings for both normal and oblique incidence also agree well with other published data. The conductor-backed coated grating is studied, and it is shown that the groove profile can be used to significantly alter the absorbing characteristics for lossy material coatings     

Contrast enhancement in the phase plate transmission electron microscopy using an objective lens with a long focal length

A new optical condition using an objective lens (OL) of a long focal length (objective mini lens: OM) was tested to enhance image contrast in phase plate transmission electron microscopy (P-TEM). A phase plate was set on the selected area aperture plane where diffraction patterns were formed under the optical condition using the OM. A phase shift by the phase plate was added to the electron waves to visualize phase objects. The application of the OM to the P-TEM should provide higher phase contrast than that obtained by the OL for the phase objects. One of the reasons for the contrast enhancement is that high-angle scattering electron waves which would give the background intensity were not used for image formation due to the large spherical aberration. Another reason is that the cut-on frequency above which the phase shift was added by the phase plate could be smaller using the OL with a long focal length. Experimental results and model calculations showed the contrast enhancement of the biological specimens using the OM.     

The HgCdTe electron avalanche photodiode

Electron injection avalanche photodiodes in short-wave infrared (SWIR) to long-wave infrared (LWIR) HgCdTe show gain and excess noise properties indicative of a single ionizing carrier gain process. The result is an electron avalanche photodiode (EAPD) with “ideal” APD characteristics including near noiseless gain. This paper reports results obtained on long-, mid-, and short-wave cutoff infrared Hg_1−xCd_xTe EAPDs (10 μm, 5 μm, and 2.2 μm) that use a cylindrical “p-around-n” front side illuminated n+/n-/p geometry that favors electron injection into the gain region. These devices are characterized by a uniform, exponential, gain voltage characteristic that is consistent with a hole-to-electron ionization coefficient ratio, k=α_h/α_e, of zero. Gains of greater than 1,000 have been measured in MWIR EAPDS without any sign of avalanche breakdown. Excess noise measurements on midwave infrared (MWIR) and SWIR EAPDs show a gain independent excess noise factor at high gains that has a limiting value less than 2. At 77 K, 4.3-μm cutoff devices show excess noise factors of close to unity out to gains of 1,000. A noise equivalent input of 7.5 photons at a 10-ns pulsed signal gain of 964 measured on an MWIR APD at 77 K provides an indication of the capability of this new device. The excess noise factor at room temperature on SWIR EAPDs, while still consistent with the k=0 operation, approaches a gain independent limiting value of just under 2 because of electron-phonon interactions expected at room temperature. The k=0 operation is explained by the band structure of the HgCdTe. Monte Carlo modeling based on the band structure and scattering models for HgCdTe predict the measured gain and excess noise behavior.     

The grid lens effect in convergent Pierce guns

In a conventional Pierce-type gun, the anode aperture causes a potential reduction in the cathode-anode region from the ideal Langmuir potential distribution. For low-voltage gating of the electron beam, a mesh grid of spherical shape (conforming to an equipotential surface) is used in front of the cathode. When this grid is operated at the Langmuir potential depicted by its relative position, there is a difference in the potential gradients on its two sides. This difference causes a lens action at each mesh element which results in a displacement of the actual electron trajectory from the ideal laminar trajectory in the region beyond the anode. A means for calculating these displacements as a function of distance along the axis is developed. As the grid lenses are divergent, the images of the mesh elements in any plane beyond the anode are larger than those for ideal laminar flow, resulting in a current density distribution which differs from that of the ideal beam. A means of calculating the current density profile by summing the effects of the grid lenses is devised, and the method is applied to a sample gun design to illustrate the effect on the current density distribution.     

The geometric-optics theory of a plane chiral-metamaterial lens

The focusing properties of a double-layer plate (plane lens) made of isotropic chiral electromagnetic media with negative permittivity and permeability are considered.     

The hyperboloidal lens with laterally displaced dipole feed

The hyperboloidal lens antenna with an electric dipole feed located at its focal point radiates no cross-polarized fields. The cross-polarization levels generated by the lateral displacement of the dipole feed are computed, as well as the beam deviation factor, coma lobe level, gain degradation, and radiation pattern. Results are presented as a function of lens parameters.     

Observations on oblique projectors and pseudoinverses

Oblique projectors (which were examined by Behrens and Scharf (see ibid., vol.42, no.6, p.1413-24, 1994)) are related to earlier work on oblique pseudoinverses and constrained least-squares methods and are reconsidered from the standpoint of orthogonal basis vectors and QR factorizations. Construction algorithms are presented that are numerically more stable than the normal-equations constructions previously used     

斜入射消色差相位延迟器的优化设计

探讨了斜入射型的消色差相位延迟器的全内反射角随折射率的变化规律,从而得出斜入射型的消色差相位延迟器的延迟量受折射率及全内反射角变化的复合影响,为设计斜入射时的高精度消色差相位延迟器提供了新理论依据.     

Image recognition using iterative oblique projection

A new robust method for image recognition based on iterative oblique projection is presented. By oblique projection, both the unstructured and structured noises can be suppressed. To improve recognition accuracy, an iterative process is adopted to reduce interference further. Experiments show that the proposed approach offers better performance than the conventional template matching method.