软X射线多层膜设计中表面粗糙度对反射率的影响

给出了一种改进的软X射线波段的多层膜设计方法.在设计过程中,考虑了反射镜基底和各膜层之间的均方(RMS)粗糙度对反射率的影响 ;在Stearns提出的散射理论的基础上给出了粗糙界面的数学模型.文中以波长为λ=1.03nm的软X射线为例进行设计,设计结果表明 :要使波长为λ=1.03nm的多层膜的反射率大于10%,反射镜基底的均方粗糙度不应超过0.6nm.实验中选择几块表面粗糙度为 0.5nm(RMS)的熔石英平面镜作为基底来制作适用于该波长的、层对数超过70的多层膜.然后在的入射角下测量反射率,测得的值为10%,这与采用本设计方法得到的计算结果一致.该反射镜作为X射线谱仪的分光元件被应用于惯性约束聚变(ICF)的过程诊断中.     

Manufacturing and testing of X-ray imaging components with high precision

1Introduction X rayimagingtechnologyhasbeenoneof themostimportantresearchcontentssince RoentgendiscoveredX rayin1895.Initially,X raywasusedtostudytheinternalstructureof substancesbycontactradiography.Thespeci menisplacedincontactwithaphotographicfilm duringtheX rayexposure.Theimageofthe specimenisdisplayedafterdeveloping.The methodhasbeenuseduntilnow,anditiswidely appliedinmedicaltreatmentandinnerflawsde tectionofindustrialmaterials.Sincetherefractiveindicesofmaterialsin X rayrangearelowert…     

Inducing superconductivity at a nanoscale: photodoping with a near-field scanning optical microscope

The local modification of an insulating GdBa2Cu3O6.5 thin film, made superconducting by illumination with a near-field scanning optical microscope (NSOM), is reported. A 100-nm aperture NSOM probe acts as a sub-wavelength light source of wavelength lambda(exc) = 480-650 nm, locally generating photocarriers in an otherwise insulating GdBa2-Cu3O6.5 thin film. Of the photogenerated electron-hole pairs, electrons are trapped in the crystallographic lattice, defining an electrostatic confining potential to enable the holes to move. Reflectance measurements at lambda = 1.55 microm at room temperature show that photocarriers can be induced and constrained to move on a approximately 200 nm scale for all investigated lambda(exc). Photogenerated wires present a superconducting critical temperature Tc= 12 K with a critical current density Jc = 10(4) A cm(-2). Exploiting the flexibility provided by photodoping through a NSOM probe, a junction was written by photodoping a wire with a narrow (approximately 50 nm) under-illuminated gap. The strong magnetic field modulation of the critical current provides a clear signature of the existence of a Josephson effect in the junction.     

Compact electrostatic beam optics for multi-element focused ion beams: simulation and experiments

Electrostatic beam optics for a multi-element focused ion beam (MEFIB) system comprising of a microwave multicusp plasma (ion) source is designed with the help of two widely known and commercially available beam simulation codes: AXCEL-INP and SIMION. The input parameters to the simulations are obtained from experiments carried out in the system. A single and a double Einzel lens system (ELS) with and without beam limiting apertures (S) have been investigated. For a 1 mm beam at the plasma electrode aperture, the rms emittance of the focused ion beam is found to reduce from ～0.9 mm mrad for single ELS to ～0.5 mm mrad for a double ELS, when S of 0.5 mm aperture size is employed. The emittance can be further improved to ～0.1 mm mrad by maintaining S at ground potential, leading to reduction in beam spot size (～10 μm). The double ELS design is optimized for different electrode geometrical parameters with tolerances of ±1 mm in electrode thickness, electrode aperture, inter electrode distance, and ±1° in electrode angle, providing a robust design. Experimental results obtained with the double ELS for the focused beam current and spot size, agree reasonably well with the simulations.     

大口径轻质反射镜坯的制造

给出了制造大口径轻质反射镜坯的机械法减重技术及所制造的反射镜坯.在镜坯制造过程中通过计算机辅助设计搜索轻量化加工区域的形状、大小、深度,并对其进行分类标识;编辑TPH(toolpath)轨迹数据文件,编写CNC(comput ernumbercontrol)数控系统的零件加工程序,由数控系统在图形方式下控制实际加工.同时采用化学方法消除加工过程中产生的应力与微小裂纹.加工出的大口径轻质反射镜坯达到设计要求,轻量化率达到65%以上,加工后的非球面面形精度达到0.029λ(rms,λ=633nm).制造过程中在不同支撑状态下,变形量很小,保持了非球面面形精度稳定性,显示出了结构的稳定性.该方法已经成为大口径反射镜制造的关键支撑技术.     

Compact high-aperture interferometer with a diffractive reference wave for high-precision referenceless aberration measurements of optical elements and systems

We present the optical layout and actual design of a compact high-aperture referenceless point diffraction interferometer with a diffraction reference wave. The basic concept of this interferometer is based on a single-mode optical fibre with a subwave output aperture, which is used as a source of spherical reference waves. The interferometer is designed for high-precision measurements of the surface shape and aberrations of optical elements. It makes use of a diffraction reference wave and is developed for mass industrial applications. The proposed design does not require the involvement of special external conditions, and reduces the need for calibrated reference surfaces. We evaluate the performance of our interferometer for highprecision measurements and demonstrate its use by presenting results obtained from measuring the shapes of spherical references from various manufacturers and the aberration of a five lens objective.     

H- beam extraction from a cesium seeded field effect transistor based radio frequency negative hydrogen ion source

H(-) beam was successfully extracted from a cesium seeded ion source operated using a field effect transistor inverter power supply as a radio frequency (RF) wave source. High density hydrogen plasma more than 10(19) m(-3) was obtained using an external type antenna with RF frequency of lower than 0.5 MHz. The source was isolated by an isolation transformer and H(-) ion beam was extracted from a single aperture. Acceleration current and extraction current increased with the increase of extraction voltage. Addition of a small amount of cesium vapor into the source enhanced the currents.     

An optical spectrometer for a confocal scanning laser microscope

An optical spectrometer for the visible range has been developed for the confocal scanning laser microscope (CSLM) Phoibos 1000. The spectrometer records information from a single point or a user-defined region within the microscope specimen. A prism disperses the spectral components of the recorded light over a linear CCD photodiode array with 256 elements. A regulated cooling unit cools the diode array, thereby reducing the detector dark current to a level, which allows integration times of up to 60 s. The spectral resolving power, λ/Δλ, ranges from 400 at λ = 375 nm to 100 at λ = 700 nm. Since the entrance aperture of the spectrometer has the same diameter as the detector aperture of the CSLM, the three-dimensional spatial resolution for spectrometer readings is equivalent to that of conventional confocal scanning, that is, down to 0.2 μm lateral and 0.8 μm axial resolution with an N.A.=1.3 objective.     

纳米级针孔矢量衍射波前误差分析

应用哈特曼-夏克(H-S)波前检测仪检测大数值孔径(NA)透镜时,需要采用纳米级针孔产生参考球面波前对H-S传感器进行标定.为了制作出满足要求的高质量针孔,本文对影响参考波前质量的各种要素进行了仿真计算和分析,以获得最优针孔加工参数.基于矢量衍射理论,在会聚高斯光束照射下,计算了针孔厚度和直径大小对衍射波前误差的影响,衍射波前中的像差成份、能量透过率、强度均匀性、针孔加工误差及光束相对针孔中心发生平移、离焦、倾斜时衍射波前误差的变化.分析计算显示,在NA为0.6时,为了使相对于理想球面波的波峰波谷值(P-V)偏差不大于0.005λ(λ=193 nm),在实际针孔的加工制作中,应选取材料铬,并取厚度200 nm,直径180 nm为适宜.     

Design and performance of a thermal actuator driving a preloaded linear translation stage

A thermally actuated, single-axis, bidirectional translation stage is designed and constructed. To increase the temperature of the thermal actuator, induction heating is used while air-water-mist cooling is used to decrease the temperature. An automated control strategy comprising PID closed loop control (for heating) and On/Off switching between air and mist control (for cooling) is described. The translation stage of this study produces a displacement range of 100 μm and 200 μm (using 240 W and 480 W power sources) in the presence of preloads up to 1 kN. Dependent on the power source used, the root mean square (rms) controller error at steady-state is within 15 nm (240 W) and 35 nm (480 W). No significant variation in the rms controller error was measured in the presence of the different preloads. Dynamic performance is evaluated from step responses over the full range of the actuator as well closed-loop frequency responses. The non-linear, asymmetric aspects of heating and cooling are discussed. Further observations of the system behavior and the preload effect are presented with discussion covering the slew rate, magnitude of overshoot, and controller settling time.     

Near-field fluorescence imaging of single molecules with a resolution in the range of 10 nm

We demonstrate fluorescence imaging of single molecules, by near-field scanning optical microscopy (NSOM), using the illumination-collection mode of operation, with an aperture probe. Fluorescence images of single dye molecules were obtained with a spatial resolution of 15 nm, which is smaller than the diameter of the aperture (20 nm) of the probe employed. Such super-resolution may be attributable to non-radiative energy transfer from the molecules to the coated metal of the probe since the resolution obtained in the case of conventional NSOM is limited to 30–50 nm due to penetration of light into the metal.     

Determination of scattering structures from spatial coherence measurements

A new method of structure determination and microscopic imaging with short-wavelength radiations (charged particles, X-rays, neutrons), based on measurements of the modulus and the phase of the degree of spatial coherence of the scattered radiation, is developed. The underlying principle of the method--transfer of structural information about the scattering potential via spatial coherence of the secondary (scattering) source of radiation formed by this potential--is expressed by the generalization of the van Cittert-Zernike theorem to wave and particle scattering [A.M. Zarubin, Opt. Commun. 100 (1993) 491; Opt. Commun. 102 (1993) 543]. Shearing interferometric techniques are proposed for implementing the above measurements; the limits of spatial resolution attainable by reconstruction of the absolute square of a 3D scattering potential and its 2D projections from the measurements are analyzed. It is shown theoretically that 3D imaging with atomic resolution can be realized in a "synthetic aperture" electron or ion microscope and that a 3D resolution of about 6 nm can be obtained with a "synthetic aperture" X-ray microscope. A proof-of-principle optical experiment is presented.     

Matrix of small-radius radio-frequency discharges as a volume-production based source of negative hydrogen ions

Based on experience from a work--both theoretical and experimental one--on negative hydrogen ion beam sources studied regarding fusion applications, a novel design of a rf source with volume production of the ions is proposed. The suggestion is for a source constructed as a matrix of small-radius tandem discharges (with magnetic filters largely extended over the discharge length), inductively driven (by a single coil, for the whole matrix) and with a single aperture extraction from each of them.     

A microcontroller-based variable voltage variable frequency sinusoidal power source with a novel PWM generation strategy

The present paper describes the development of a low cost, microcontroller-based variable voltage variable frequency sinusoidal power source, which is the demand of the day for various applications. The power source is developed using MOSFET H-bridge inverter and with a stand alone LCD display system. The design methodology proposes to utilize a novel concept of generating sinusoidal pulse width modulation signals for the driver circuit of the inverter. The system proposes to incorporate a ROM-based LUT within the power source itself for the sinusoidal signal generation with enhanced stability. This low cost, yet accurate power source has been successfully developed for wide range of voltage commands (30-80 V rms) and frequency commands (40-70 Hz), and their real-life performances in voltage wave generation were also found to be quite satisfactory.     

Single molecule mapping of the optical field distribution of probes for near-field microscopy

The most difficult task in near-field scanning optical microscopy (NSOM) is to make a high quality subwavelength aperture probe. Recently, we have developed high definition NSOM probes by focused ion beam (FIB) milling. These probes have a higher brightness, better polarization characteristics, better aperture definition and a flatter end face than conventional NSOM probes. We have determined the quality of these probes in four independent ways: by FIB imaging and by shear-force microscopy (both providing geometrical information), by far-field optical measurements (yielding throughput and polarization characteristics), and ultimately by single molecule imaging in the near-field. In this paper, we report on a new method using shear-force microscopy to study the size of the aperture and the end face of the probe (with a roughness smaller than 1.5 nm). More importantly, we demonstrate the use of single molecules to measure the full three-dimensional optical near-field distribution of the probe with molecular spatial resolution. The single molecule images exhibit various intensity patterns, varying from circular and elliptical to double arc and ring structures, which depend on the orientation of the molecules with respect to the probe. The optical resolution in the measurements is not determined by the size of the aperture, but by the high optical field gradients at the rims of the aperture. With a 70 nm aperture probe, we obtain fluorescence field patterns with 45 nm FWHM. Clearly, this unprecedented near-field optical resolution constitutes an order of magnitude improvement over far-field methods like confocal microscopy.     

有孔金属导体板屏蔽特性的分析

对电小孔的耦合理论进行了总结,给出了计算具有电小孔的无限大金属导体板屏蔽效能的一般方法,讨论和分析了平面波源情况下不同形状孔对屏蔽效能的影响,通过数值计算,得出了一些有意义的结论。     

Single molecule mapping of the optical field distribution of probes for near-field microscopy

The most difficult task in near-field scanning optical microscopy (NSOM) is to make a high quality subwavelength aperture probe. Recently, we have developed high definition NSOM probes by focused ion beam (FIB) milling. These probes have a higher brightness, better polarization characteristics, better aperture definition and a flatter end face than conventional NSOM probes. We have determined the quality of these probes in four independent ways: by FIB imaging and by shear-force microscopy (both providing geometrical information), by far-field optical measurements (yielding throughput and polarization characteristics), and ultimately by single molecule imaging in the near-field. In this paper, we report on a new method using shear-force microscopy to study the size of the aperture and the end face of the probe (with a roughness smaller than 1.5 nm). More importantly, we demonstrate the use of single molecules to measure the full three-dimensional optical near-field distribution of the probe with molecular spatial resolution. The single molecule images exhibit various intensity patterns, varying from circular and elliptical to double arc and ring structures, which depend on the orientation of the molecules with respect to the probe. The optical resolution in the measurements is not determined by the size of the aperture, but by the high optical field gradients at the rims of the aperture. With a 70 nm aperture probe, we obtain fluorescence field patterns with 45 nm FWHM. Clearly, this unprecedented near-field optical resolution constitutes an order of magnitude improvement over far-field methods like confocal microscopy.     

Intense beams from gases generated by a permanent magnet ECR ion source at PKU

An electron cyclotron resonance (ECR) ion source is designed for the production of high-current ion beams of various gaseous elements. At the Peking University (PKU), the primary study is focused on developing suitable permanent magnet ECR ion sources (PMECRs) for separated function radio frequency quadrupole (SFRFQ) accelerator and for Peking University Neutron Imaging Facility. Recently, other kinds of high-intensity ion beams are required for new acceleration structure demonstration, simulation of fusion reactor material irradiation, aviation bearing modification, and other applications. So we expanded the ion beam category from O(+), H(+), and D(+) to N(+), Ar(+), and He(+). Up to now, about 120 mA of H(+), 83 mA of D(+), 50 mA of O(+), 63 mA of N(+), 70 mA of Ar(+), and 65 mA of He(+) extracted at 50 kV through a φ 6 mm aperture were produced by the PMECRs at PKU. Their rms emittances are less than 0.2 π?mm?mrad. Tungsten samples were irradiated by H(+) or He(+) beam extracted from this ion source and H∕He holes and bubbles have been observed on the samples. A method to produce a high intensity H∕He mixed beam to study synergistic effect is developed for nuclear material irradiation. To design a He(+) beam injector for coupled radio frequency quadruple and SFRFQ cavity, He(+) beam transmission experiments were carried out on PKU low energy beam transport test bench and the transmission was less than 50%. It indicated that some electrode modifications must be done to decrease the divergence of He(+) beam.     

Effect of Surface Waves from a Moving Object on Its Image During Reconstruction using Aperture Synthesis

The reconstruction of an image of the cross section of a thin wire obtained by an ultrasonic detector in an aqueous medium at a frequency of 1.3 MHz with a monochromatic probing signal is considered. The image was reconstructed using a synthesized aperture by correlation processing of a trajectory Doppler signal with calculated reference trajectory signals from point objects. The disturbing effect of the ultrasonic wave reflected from the surface wave generated by the moving wire on the image reconstruction is taken into account. The results of reconstruction of the image of the wire cross-section from model and experimental trajectory signals in the presence of a surface wave are given.