Stability of a light beam in a beam waveguide

Long-distance, high-capacity transmission using a light beam in a beam waveguide is an attractive project for optical communications. However, the transmission of energy in the form of a beam gives rise to a new problem, that is, the stability of a sharp beam. In this paper, the stability problems of a Gaussian beam in a beam waveguide are presented. The deflection and the spot-size variation of a beam in the waveguide with known imperfections, such as transverse displacements of lenses, variation in focal length, and so on, are studied. If the transverse displacements of the lenses are periodic in space, instability of the beam path may occur. The unstable condition is derived. The variation of the spot size at the lenses is obtained in terms of small perturbations of the ideal waveguide. If the incident beam from a laser is not matched to the mode of the waveguide, the spot size at the lenses varies periodically. Statistical results for the models of a waveguide with random lenses, having random transverse position, random spacing, and random focal length, are also given.     

Further Investigations with an Optical Beam Waveguide for Long Distance Transmission

Measurements made with an optical beam waveguide employing quartz lenses for the beam iteration demonstrate that a transmission loss of 0.5 dB/km is readily obtainable, and that this loss is solely determined by the absorption, scatter, and reflection losses of the lenses. The transmission loss and its variation depends on the air pressure along the light path. Photometric measurements of the energy distribution of the transmitted beam illustrate that distortions in the mode pattern of the laser are the major cause of the launching loss which for the available laser was measured to be approximately 0.4 dB.     

Near-field probe measurements of microwave scattering from discontinuities in planar surfaces

In microwave scattering, nonradiating fields may contribute to radiating fields by local perturbations such as geometric discontinuities or variations in impedance or electromagnetic properties. Near-field measurements of scattering bodies provide insight into these scattering mechanisms by measuring both radiated and nonradiated fields. In this research, an H-field probe measured scattering from simple discontinuities in planar bodies at frequencies between 2 and 10 GHz. Illumination of the test-body was furnished by a focused lens system with a Gaussian-like tapered beam that locally illuminated inhomogeneities on the body. Measured data and model calculations are presented for scattered H-fields near canonical discontinuities (e.g. gaps and edges in conducting planes). Calculations of the plane wave spectrum of the measured and modeled data were used to distinguish specular reflected components from surface modes. A focused beam was simulated in a finite-difference time-domain (FDTD) model with a weighted sum of plane waves. FDTD results agreed with the measured near-field data.     

强激光的时间整形和空间整形——利用双折射透镜组实现激光束的空间整形

本文使用琼斯矩阵方法对双折射透镜组空间整形系统的光强透射率分布和工作特性进行了分析,并讨论了工程设计中参数的选择以及加工误差带来的影响等有关问题.     

Comparison between different imaging modes in focussed ion beam instruments

In a two-lens focussed ion beam instrument, one can choose to either have a crossover in between the lenses or not. For a representative instrument, it is shown that the optimized probe size of the non-crossover mode is smaller than that of the crossover mode. Both the lens aberrations and the statistical Coulomb effects are responsible for this effect. We analyzed the differences for a large range of beam currents and found that in the absence of statistical Coulomb interactions, the difference can be as much as a factor 1.6. In the presence of Coulomb interactions, the difference increases to a factor 1.8.     

电子束聚焦偏转系统中透镜和偏转器不对中装配误差效应的数值计算

本文讨论了透镜和偏转器在电子束系统中不对中装配造成的电子光学性质影响的数值计算问题,包括推导出不对中的透镜和偏转器在系统中的电磁场表示式,电子轨迹方程及象差积分式等。根据这些公式所编制的计算机程序已用来计算了若干个实例,从中可见不对中误差效应的数值计算对于设计和装配电子束聚焦偏转系统起到指导性的作用。     

基于ZEMAX的半导体激光准直镜设计方法研究

针对目前采用单个球面镜压缩激光时存在发散角效果差或者球面镜片数过多的问题,通过ABCD矩阵法从理论上对高斯光束经过单透镜时的传输特性进行了分析,得出了单透镜无法实现半导体激光光束理想准直的结论。提出了一种基于ZEMAX的半导体光源准直镜的设计方案,并给出了设计与优化方法。结合工程中常用的808nm半导体激光器,设计了双片型808nm半导体激光准直镜,并在ZEMAX中使用合适的优化函数和权重对像差进行了校正。通过采用非球面镜获得了较好的准直效果,发散角达到了0．032mrad。该设计使用的镜片数较少,结构简单。     

Discontinuities Appear in the Repeller Current of a Reflex Klystron Detector

It is known that reflex klystrons are usable as microwave detectors. When the repeller current was plotted against acceleration grid (which is anode) voltage, Koctienko, Deviatkov, and Lebed found discontinuities. Whitford did not find these discontinuities for the 726A reflex klystron. Koctienko, et al., explained that the discontinuities were attributed to the appearance and disappearance of the virtual cathode when the klystron began or stopped oscillation. Whitford explained that the beam current density of the 726A reflex klystron was sufficiently high to maintain the virtual cathode at all times.     

Optimization of the quadrupole probe-forming system with individual power supplies for lenses

This study reviews a quadruplet of magnetic quadrupole lenses, where each lens is fed from an individual power supply. In this case the power supplies of two last lenses (along the course of the beam) are selected from the condition of ensuring the stigmatic focusing, while the power supply values of two first lenses are free parameters. These parameters form a two-parameter set, where the functional characterizing the acceptance of a probe-forming system is determined. It has been shown that the use of four individual power supplies for lenses in the quadruplet allows us to make the acceptance more than two times larger.     

Some Aspects of Beam Waveguides for Long Distance Transmission at Optical Frequencies

Two types of beam waveguides are discussed in this paper, the iris-type and the lens-type. Both appear applicable to guided long distance transmission of light with theoretical losses of less than 1 db/km. However, there are problems concerning their practicability which require experimental investigation. Such problems are the alignment of the irises or the lenses, the effects of turbulence and stratification of air along the light path, and the required tolerance in the construction of the lenses. Since the lens-type guide offers a simple possibility for compensating misalignments, an experimental waveguide of this type has been constructed, having a length of approximately 1 km and comprising 10 iterations. The light path is enclosed by a 4 inch aluminum pipe which is supported within a 6 inch aluminum pipe. The first series of experiments which is reported in this paper indicated that there are no serious alignment problems. However, it was found that the effects of turbulence and air stratification are usually very severe and it appears necessary to provide an evacuated light path to obtain constant transmission conditions. It was also found that the available lenses add considerably higher iteration loss than expected. This increased loss was primarily caused by inadequate surface coating. A theoretical study of beam propagation in a misaligned lens-type guide is included in the Appendix.     

Electron-beam microcolumn fabrication and testing

In this paper, we report the improvement of a process for full microfabrication of miniaturized electron lenses specially design for low-energy (100 eV) lithography tools. The main advantages of this technique are the following. It is batch processing oriented, meaning that lenses can be easily built in a full wafer fabrication. With this procedure it is possible to develop a completely integrated process for machining arrays of lenses. Lens bores are aligned using an electron lithography process, resulting in highly accurate positioning. Finally, the source lens chip has not only one but several sets of lenses with different aperture-sizes, each producing a different beam diameter. A scheme is proposed with which the appropriate lens can be selected by means of a deflection system.     

高斯光束经含失调透镜的猫眼系统反射特性研究

为了分析猫眼光学系统中透镜失调对高斯光束反射特性的影响,将分划板的光瞳函数展为有限项复高斯函数之和,并利用适用于失调光学系统的广义衍射公式,求解了高斯光束经含失调透镜的猫眼光学系统的反射光场近似解析式,针对给定猫眼光学系统定量分析了透镜失调量对反射光束场分布的影响.结果表明,透镜的角位移比横位移对反射光束传输特性的影响...     

On the Theory of Randomly Misaligned Beam Waveguides

A straightforward method for the determination of the expected attenuation in misaligned beam waveguides is presented. It applies to confocal guides and assumes that the misalignment consists of random displacements of the lenses in directions perpendicular to the beam axis. Reiterative fields, as they are present in perfectly aligned beam waveguides, do not exist in misaligned guides. However, it can be shown that there are beams whose expected field distribution is repeated from lens to lens. These "statistical modes" are determined by the eigenfunctions of a homogeneous integral equation of the second kind. The corresponding eigenvalues determine the expected attenuation per iteration. The absolute squares of the eigenvalues yield an upper bound for the expected power loss per iteration. The integral equation is solved for small mean square displacements of the lenses by a perturbation method. For infiitely extended lenses, the equation can be solved in closed form. In both cases the expected attenuation of the lower-order statistical modes has been calculated; the results are shown as function of the mean square displacement of the lenses.     

梯度折射率纤维透镜新的成象公式

利用高斯光束传播理论以及ABCD定律,导出了梯度折射率纤维透镜新的成象公式。     

提高半导体激光二极管功率密度的光束整形方法

针对半导体激光二极管由束散角大（14~46）导致的激光功率密度在传播过程中不断衰减的问题,提出了一种提高激光功率密度的光束整形方法。首先以X型柱面平凸透镜和Y型柱面平凸透镜对激光二极管输出光束慢轴和快轴方向进行准直,然后通过一对平凸透镜组合进行扩束,进一步提高光束平行度,最后由单片平凸透镜将光束聚焦为高功率密度的光点。采用Light Tools软件仿真光路、优化光学元件参数,对光学元件进行实际选型后安装并调试光束整形系统。测试结果表明:半导体激光二极管输出光束的67%激光能量汇聚于直径1 mm圆内,激光功率密度优于30 W/cm2。     

基于ZEMAX的半导体激光器匀光设计

为了满足半导体激光器能量均匀化的应用需求,基于ZEMAX光学设计软件设计了一套光束整形匀光系统。采用非球面镜与倒置柱面镜望远系统的透镜组合对单模半导体激光器进行准直,得到近似高斯圆光斑;在推导了基模高斯强度分布的匀光投影半径的基础上,利用ZEMAX优化得到两个非球面镜组成的匀光透镜组,在一定范围内可获得能量均匀度达96%以上的圆光斑。同时,实现了一个大功率半导体激光器光纤耦合模块的能量匀化设计,满足对能量匀化要求较高的应用。结果表明,该研究为半导体激光器能量均匀化的应用提供了有效方法。     

发散纤维透镜新的成象公式

本文利用高斯光束传播理论以及ABCD定律,导出了发散纤维透镜新的成象公式。     

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.     

湍流大气对高斯光束聚焦特性的影响

基于广义惠更斯-菲涅尔原理,推导出高斯光束在湍流大气中经薄透镜聚焦后的光强解析表达式,进而得到轴上点最大光强和相对焦移的公式。对表达式进行的数值仿真结果表明,湍流大气中高斯光束的聚焦规律与自由空间中高斯光束的聚焦规律相同,湍流大气对高斯光束聚焦特性的影响表现为,使得轴上点最大光强减小、相对焦移增大。因此,为在探测器上获得最大光强和较小的相对焦移,应采用大束腰高斯光束通过短焦距透镜进行聚焦。