High speed two-dimensional optical beam position detector

Disclosed is the design of a high speed two-dimensional optical beam position detector which outputs the X and Y displacement and total intensity linearly. The experimental detector measures the displacement from DC to 123 MHz and the intensity of an optical spot in a similar way as a conventional quadrant photodiode detector. The design uses four discrete photodiodes and simple dedicated optics for the position decomposition which enables higher spatial accuracy and faster electronic processing than conventional detectors. Measurements of the frequency response and the spatial sensitivity demonstrate high suitability for atomic force microscopy, scanning probe data storage applications, and wideband wavefront sensing. The operation principle allows for position measurements up to 20 GHz and more in bandwidth.     

High brightness sources for electron and ion beam microscopy and micro-lithography

High brightness sources are crucial to the success of any electron- or ion-optical instrument. As a result of the researches of the Cornell group, the understanding and development of high brightness electron sources has led to improved forms of scanning transmission electron microscopes and advanced micro-lithography systems. Many of the basic concepts involved can be transferred to high brightness field ion emission guns now needed for high resolution scanning ion microscopes and ion beam lithography systems.     

A source of a high-power relativistic electron beam with high brightness

A ribbon diode of a U-2 accelerator (800 kV, ∼30 kA) intended for generating a high-intensity electron beam for heating plasma in a GOL-3 multimirror magnetic trap (Budker Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences) is described. The parameters of the beam characterized by a high brightness (∼7 kA/(cm² sr)) in a magnetic field of ∼5 T resulting from a numerical simulation of the beam formation process are presented. The results of simulation of the beam transport and transformation of the profile of its cross section during movement of electrons in a curvilinear guiding magnetic field are presented. The calculated cross section is compared to the beam imprint on a target.     

Avalanche photodiode based detector for beam emission spectroscopy

An avalanche photodiode based (APD) detector for the visible wavelength range was developed for low light level, high frequency beam emission spectroscopy (BES) experiments in fusion plasmas. This solid state detector has higher quantum efficiency than photomultiplier tubes, and unlike normal photodiodes, it has internal gain. This paper describes the developed detector as well as the noise model of the electronic circuit. By understanding the noise sources and the amplification process, the optimal amplifier and APD reverse voltage setting can be determined, where the signal-to-noise ratio is the highest for a given photon flux. The calculations are compared to the absolute calibration results of the implemented circuit. It was found that for a certain photon flux range, relevant for BES measurements (≈10(8)-10(10)?photons/s), the new detector is superior to both photomultipliers and photodiodes, although it does not require cryogenic cooling of any component. The position of this photon flux window sensitively depends on the parameters of the actual experimental implementation (desired bandwidth, detector size, etc.) Several detector units based on these developments have been built and installed in various tokamaks. Some illustrative results are presented from the 8-channel trial BES system installed at Mega-Ampere Spherical Tokamak (MAST) and the 16-channel BES system installed at the Torus Experiment for Technology Oriented Research (TEXTOR).     

基于CCD的双光束多波长紫外可见吸收检测器

由于传统的多波长紫外可见吸收检测器无法克服光源波动造成的噪声和漂移,故设计开发了一种基于CCD的双光束多波长紫外可见吸收检测器.光源发出的光聚焦后被分束镜分成信号光和参考光,信号光射入到样品检测池中.从样品检测池中出射的信号光经过斩光器聚焦在狭缝上,被凹面光栅分光成像于CCD的一部分光敏面上.参考光在CCD的另一部分光敏面上分光成像.在光路系统和外围电路的辅助配合下,可以用一片CCD实现信号光谱,参考光谱和暗电流的精确测量.由于采用参考光光谱和CCD暗电流对信号光谱进行实时补偿,可以使基线短期噪声降低为1×10-5 AU,漂移降低为1×10-4 AU/h.     

Ten-microsecond pulsed molecular beam source and a fast ionization detector

We describe a pulsed gas valve which we have developed for use as a molecular beam source. In order to observe the performance of the pulsed beam source, we also have developed an ionization detector with a rise time of about 1 micros. The pulsed valve produces very intense supersonic molecular beam pulses of about 10 micros duration for light gases such as H2 and He, and of somewhat longer duration for heavier gases. As a new tool for the study of molecular collisions, the pulsed beam technique offers substantial advantages over the conventional continuous-beam method for experiments which are limited by the signal-to background ratio for scattered products.     

光电/量热复合式近红外高能激光光斑探测器

为了准确测量高能激光系统远场到靶总能量和功率密度时空分布等参数,本文提出了量热吸收法和光电探测阵列法相结合的复合式测量方法.该方法由热吸收体测量入射激光的总能量,由光电探测阵列测量光斑的时空分布.研制了用于大面积、长脉冲近红外高能激光测量的复合式光斑时空分布探测器.探测器主要由石墨热吸收体、近红外探测器阵列、测温单元和信号处理单元等组成,有效测量光斑面积达到22 cm×22 cm,光斑测量空间分辨力为1.1 cm,时间分辨力为20 ms.该测量系统同时兼顾了光电探测阵列法的高时空分辨能力和量热吸收法的低测量不确定度等优点,适合于高能量、大面积近红外高能激光光斑参数的综合测量,并已成功应用于外场实验.     

A detector for imaging of explosions on a synchrotron radiation beam

Synchrotron radiation (SR) offers a unique chance to study the structure of a substance in fast processes. Since SR is emitted by electron bunches in a storage ring, the SR burst corresponding to a single bunch may be very short. Should a detector capable of detecting SR from a single bunch without mixing signals from different bunches be available, it is possible to obtain information on changes in the state of the material in a sample under investigation with a very high time resolution. A detector for imaging of explosions on an SR beam—DIMEX—has been developed by the Budker Institute of Nuclear Physics (Siberian Division of the Russian Academy of Sciences, Novosibirsk). This detector is a high-pressure ion-ization chamber with a strip readout at a pitch of 0.1 mm. The electron component of primary ionization is collected within 50 ns, which is substantially shorter than the orbital period of a bunch in the VEPP-3 storage ring (250 ns). The DIMEX is filled with a Xe—CO₂ mixture (3: 1) at an absolute pressure of 7 atm. The spatial resolution of the detector is ∼210 μm, and its efficiency for radiation with an energy of 20 keV is ≥50%. The dynamic range of the detector is ∼100, which allows one to measure the signal with an accuracy of ∼1%. In this case, the maximum flux of X-ray photons, at which the DIMEX operates in a linear region, is ∼10¹⁰ photons/(channel s). Today, the detector has been used in experiments aimed at studying evolution of the density in detonation waves and processes of nanoparticle production at the VEPP-3 storage ring by employing the small-angle X-ray scattering technique.     

A two-coordinate detector for a beam of atomic hydrogen or deuterium

The profile of an atomic beam in the region where it forms is an important characteristic of a polarized atomic hydrogen (or deuterium) source. A mathematical model for a two-coordinate resistive detector of atomic hydrogen beams is presented. Metering equipment and a technique for measuring an atomic beam profile are described, and the results of our measurements are presented.Translated from Pribory i Tekhnika Eksperimenta, No. 1, 2005, pp. 141–145.Original Russian Text Copyright © 2004 by Trofimov, Vasilev, Kovalev, Kravtsov.     

Image simulation using Monte Carlo methods: Electron beam and detector characteristics

The rapid increase of computer speed allows using Monte Carlo simulation procedures for the analysis of complicated structures not only in a line scan mode but also in a three-dimensional approach similar to the scanning procedure in a scanning electron microscope. Simulation of image formation is a vital link in performing image analysis to obtain precise measurements, to provide the necessary connection between image parameters and structural dimensions, and to reflect important microscope beam and detector parameters. Monte Carlo simulation based on a single-scattering procedure was used for backscattered electron image simulation of three-dimensional multilayer and multielement structures. The procedure takes into account the effect of a solid state detector's electrical and angular characteristics and the effect of the electron beam dimensions on the image quality and artifacts.     

Absolute two-dimensional sub-micron metrology for electron beam lithography: A calibration theory with applications

A mathematical theory is presented along with some simple resulting procedures that permit an electron beam lithography machine to be calibrated by using it to make multiple observations of an imprecisely defined but stable planar object. The calibration thus obtained yields a degree of accuracy that is approximately equal to the reproducibility of the machine. For this purpose a rigid, movable grid plate is used, with grid points placed at arbitrary but more-or-less evenly distributed, fixed positions on its surface. An e-beam lithography machine with a high precision X-Y stage has been used to measure such a grid plate. Two interferometer beams, nominally parallel to the X- and Y-axes, measure stage displacements. No geometric assumptions are made concerning the stage, other than repeatability. Although the assumptions are very general, it is possible to observe the grid in just three orientations to determine both an inverse distortion function (calibration) and accurate, absolute rectangular coordinates for the grid points, providing that the absolute distance between a pair of points on the grid is known. A calibration program has been written applying the theory to the practical problem of calibrating an e-beam lithography system. Simulations based upon actual e-beam measurements confirm the theory for the practical situation. The paper concludes with suggestions for applictions to three other areas of science and technology: astronomy, optometry, and satellite geodesy.     

基于绝对式感应同步器的绝对角度测量系统

以绝对式圆感应同步器作为角度传感器,AD2S80A作为角度模数转换器, FPGA作为数字信号处理器进行双通道角度信息的粗精结合和译码,采用总体开环和数字信号处理部分闭环的方案,设计了绝对角度测量系统.介绍了该系统的实现原理、硬件结构、电路分析以及系统在提高运行速度和减小动态误差方面所采取的措施.该系统具有结构简单、工作稳定可靠、实时性高、抗干扰能力强等特点,特别适用于航天等外场环境.经过测试,该系统具有很高的动态和静态跟踪精度,其静态精度为3″.     

小型绝对式矩阵编码器

绝对式编码器具有固定起始点、读数可靠等优点。但传统的绝对式编码器码道圈数多,结构尺寸大,给某些方面的应用带来不便,希望结构尺寸小。本文介绍一种小型绝对式编码器的设计方法,其中包括:绝对式矩阵编码盘的设计;工作原理;矩阵译码方法。传统的14位绝对式编码器最小径向尺寸为φ130mm,而采用矩阵式编码盘,同样位数的编码器径向尺寸可缩小到φ65mm。     

Wire GEM detector

A wire GEM (WGEM) detector with a gas gap between meshes was constructed. The detector provides the amplification 5 × 10⁴ for the gas mixture of Ar + 20% CO₂ at atmospheric pressure. As compared with well-known GEM detectors produced by perforation the plastic plate metallized on both sides the WGEM does not suffer from breakdowns between its electrodes and the effect of accumulation of charges on holes’ walls is absent. As a result the WGEM has high reliability and stability.     

Differential light detector

A sensitive differential light detector is described which consists of two antiparallel silicon photovoltaic diodes and a current-to-voltage converter. The device is optimized to the detection of small differences in intensity. The noise and signal transfer features are considered, and an application example is given.     

The CLEO detector

The construction and performance of a large aperture magnetic detector designed for use at the Cornell Electon Storage Ring is descr bed.     

Tracers in vascular casting resins enhance backscattering brightness

Studying cast microvasculature with scanning electron microscopy has expanded our knowledge of many circulations, but need arises to determine the blood source of vascular beds that are supplied by two circulations. One way to do this is to mark the casting resin by adding a tracer compound that can be detected in the scanning electron microscope. A potential method of distinguishing different substances is to detect the backscattered electrons that are emitted from the tracer if the tracer is a heavier element, because heavier elements backscatter more electrons. To explore different tracers, we tested lead, titanium, iron, osmium, and uranium as solutions of different polarity and powders. The tracers were added to 1 ml of methyl methacrylate in log concentrations. Shrinkage, hardness, cast quality, and change in brightness from the tracer were compared with multivariate analysis at scanning electron microscopic working distances of 15 and 39 mm on carbon-coated and uncoated specimens. Several concentrations caused sedimentation of the tracer and prevented the resin from solidifying. Tetraethyl lead shortened the hardening time: uranyl acetate and osmium tetroxide prolonged it. Most tracers decreased shrinkage. When lead citrate and Reynolds solutions were removed, the brightness correlated with increasing atomic number, concentration of the tracer, and mean atomic number of the specimen (p <0.0001). The substances that increased contrast most were tetraethyl lead and uranium. Backscattering electron detection can distinguish methacrylate casts that have small amounts of heavier elements added to them, but an optimal tracer has not yet been established.     

天空背景亮度测量系统的研制

为了实时测量天空背景亮度,满足目标探测、跟踪、成像和大气探测等方面的应用需求,研制了一台具有全天空扫描与给定方向测量400~1000 nm波段范围积分辐亮度的仪器（DTL-1）。从DTL-1系统组成结构原理图详细说明了各功能部件的研制方案,给出了仪器研制的各项主要技术指标。对仪器进行了光谱辐亮度定标与恒定亮度下测量稳定性的测试实验;选取不同地区的天空辐亮度实测数据与MODTRAN5理论计算值进行了对比分析。结果表明：DTL-1稳定性测试的平均辐亮度示值为36.496W/m^2.sr,均方根误差为0.463W/m^2.sr,与MODTRAN软件模拟结果比较相对误差在20%以内。能够满足科研与实际应用对测量可靠性和精度的要求