Materials modification using intense ion beams

Pulsed intense ion beams have been developed for applications including surface modification and alloying, and thin-film and nanopowder synthesis. Rapid thermal processing with ions is quite promising for large-scale commercial use, due to the high specific ion energy deposition (joules per cubic centimeter) without reflection, and to the relative efficiency and low cost of the pulsed power ion-beam drivers compared to other high-kinetic energy alternatives. We discuss in this paper the basis for the use of ions in materials processing and the methods of beam formation and impingement on material to be treated, and give examples of recent and ongoing work in materials processing.     

Deposition and surface treatment with intense pulsed ion beams

Intense pulsed ion beams (500 keV, 30 kA, 0.5 μs) are being investigated for materials processing. Demonstrated and potential applications include film deposition, glazing and joining, alloying and mixing, cleaning and polishing, corrosion improvement, polymer surface treatments, and nanophase powder synthesis. Initial experiments at Los Alamos have emphasized thin-film formation by depositing beam ablated target material on substrates. We have deposited films with complex stoichiometry such as YBa₂Cu₃O_7−x and formed diamond-like-carbon films. Instantaneous deposition rates of 1 mm/s have been achieved because of the short ion range (typically 1 μm), excellent target coupling, and the inherently high energy of these beams. Currently the beams are produced in single shot uncomplicated diodes with good electrical efficiency. High-voltage modulator technology and diodes capable of repetitive firing, needed for commercial application, are being developed.     

Theory of instability-generated divergence of intense ion beamsfrom applied-B ion diodes

Recent advances in the analytic theory and numerical simulation of applied-B ion diodes in general and, in particular, the diodes being tested experimentally on the Particle Beam Fusion Accelerator II at Sandia National Laboratories, Albuquerque, NM, are described. Numerical simulation of these diodes using the three-dimensional particle-in-cell code QUICKSILVER and analytic stability analysis have provided new insight into the physics governing instability-induced beam divergence. Experimental evidence of these instabilities is described and compared with the theory. When simulation parameters are chosen to model present experiments, QUICKSILVER calculates beam divergence near the measured value. A new understanding of the nature of the electromagnetic instabilities and their effects on beam divergence has led to suggestions for improved diode design. A simulation of one of these design concepts shows divergence levels in the vicinity of 10 mrad, a level considered adequate for ignition experiments     

利用法拉第筒测试环形强流电子束束流

通过优化设计法拉第筒的响应电阻和分布电感,在“TPG700”平台上对无箔二极管阴极发射的环形电子束束流进行轴向测试。结果表明,无波二极管工作在低磁场(<1 T)条件下,在二极管电压较低时,优化后的法拉第筒测试获得的电子束束流前沿较慢,随着二极管电压的升高,电子束束流前沿明显变快;在强磁场(>2 T)条件下,法拉第筒测试结果与罗果夫斯基线圈测试结果一致。该结果表明,相比于罗果夫斯基线圈,法拉第筒更能准确地测试出无箔二极管的前向电子束束流。     

Estimation of time-varying co-ordinates of ion beams

A method is presented to estimate the time-varying co-ordinates of a continuous, low-energy ion beam. The method is noncontacting and exploits noise-like signals induced by the beam on electrostatic induction electrodes. Results of some preliminary experiments are also shown.     

Bessel beams from semiconductor light sources

We report on recent progress in the generation of non-diffracting (Bessel) beams from semiconductor light sources including both edge-emitting and surface-emitting semiconductor lasers as well as light-emitting diodes (LEDs). Bessel beams at the power level of Watts with central lobe diameters of a few to tens of micrometers were achieved from compact and highly efficient lasers. The practicality of reducing the central lobe size of the Bessel beam generated with high-power broad-stripe semiconductor lasers and LEDs to a level unachievable by means of traditional focusing has been demonstrated. We also discuss an approach to exceed the limit of power density for the focusing of radiation with high beam propagation parameter M². Finally, we consider the potential of the semiconductor lasers for applications in optical trapping/tweezing and the perspectives to replace their gas and solid-state laser counterparts for a range of implementations in optical manipulation towards lab-on-chip configurations.     

Positive ion oscillations in long electron beams

Positive ion oscillations occurring in a long electron beam were investigated experimentally. The predominant direction of oscillation was found to be transverse to the direction of electron flow, and the frequency of oscillation was found to be three times higher than existing theory predicts. In pulsed beams the onset time of irregularities in current flow due to positive ion formation was found to be inversely proportional to current, and in some cases positive ion effects were observed to take place within four microseconds of the beginning of the pulse.     

Si MOSFET fabrication using focused ion beams

Submicrometer focused ion beams have been used both for the maskless ion implantation of p-channel depletion-mode Si MOSFET's and for the gate lithography of n-channel enhancement-mode Si MOSFET's. B-Pt and Au-Si liquid-metal-alloy ion sources were utilized in a single-lens focusing column for the implantation and lithography steps, respectively. An 800-Å-thick Al stopping layer was used at the target to separate the lighter ions from the heavier ion species in the beams. Reasonable dc electrical characteristics were measured for the chosen device process parameters.     

光克尔快门中强绿光的自开门现象

本文报导了在光克尔快门中强绿光自开门现象,初步分析了自感应退偏振的成因。     

Shape-invariance error for axially symmetric light beams

A significant aspect of the propagation of coherent light beams is that the shape of the transverse field distribution changes. In this paper, the concepts of shape-invariance error and shape-invariance range are used to characterize such effects in a quantitative way. Applications of the theoretical analysis to some simple but significant cases are presented     

双束聚焦强红外激光引起可见荧光的光-声-光相互作用的研究

在强红外激光脉冲激发下引起BCl_3分子可见荧光,同时产生脉冲声,当这种声再进入振动激发态分子气体时,引起分子的再激发并再度引起分子分解,并发出可见荧光,即光-声-光现象。由于这种光-声-光现象对于研究激光化学及激光分离同位素的能量转移过程以及激光引起的气体动力学过程是极为重要的,所以,在本工作中使用二个同时的不重迭的强CO_2脉冲聚焦光束对此现象作了进一步的研究,得到了令人鼓舞的结果。将一束激光能量密度降至不足以引起光-声-光致荧光,然后单独加入另一束不重迭聚焦光束,在第一束激光辐照区域亦未     

微加工中的聚焦离子束直接写入技术

概述了聚焦离子束直接写入、离子研磨、离子注入及离子沉积技术。介绍了利用聚焦离子束技术在镀金硅片上研磨出的图案及制作出的各种纳米结构。聚焦离子束诱导沉积技术为将在各种科学工程领域应用的多种微结构的实现提供了可能,如聚焦离子束真空封装技术,它可被用来真空封装MEMS器件。     

Cluster beams from a Co---Nd liquid alloy ion source

A Cobalt-Neodymium Liquid Alloy Ion Source (LAIS) is investigated with respect to its cluster emission behaviour. Clusters and molecular ions were found. The influence of the source emission current on the cluster emission intensity and also on the cluster mass distribution is studied. The Co---Nd LAIS was used for writing patterning (implantation, sputtering) in a mass-selecting Focused Cluster Beam (FCB) system. Theoretical estimations were carried out concerning the use of the FCB for direct deposition at landing energies of about 100 eV / atom. First experimental results of cobalt FCBs are presented.     

Numerical simulation of intense helical electron beams with the calculation of the velocity distribution functions

The method of calculation of intense helical electron beams which allows to find the distribution function of electrons with respect to their transverse (oscillatory) and longitudinal velocities is developed. The initial velocity distribution function can be arbitrary. The data obtained in numerical simulation and experimental measurements for beams with various topologies are compared. The evolution of the transverse velocity distribution function with the beam current growth is traced. It is found that the transformation of the velocity distribution function may indicate a possible instability in a real beam.     

Reflection matrix for Gaussian light beams in FEL oscillators

The transformations of Gaussian radiation beams caused by reflection off mirrors is an important issue for the operation of free-electron lasers as oscillators. The reflected radiation from a single incident Gaussian mode will contain other modes due to the finite size, the deflection of the beam, and mismatches in the curvature. A method for analytic computation of the reflection matrix is developed. The mirror surface that reflects spherical incoming wavefronts into spherical outgoing is determined analytically. The cross coupling among vector components of the radiation field, caused by the curvature of the mirror surface, is included     

Acoustooptic interaction of two light beams in a paratellurite crystal

Double acoustooptic diffraction of light in a paratellurite crystal is investigated experimentally and theoretically. The anisotropic Bragg interaction with three diffraction maxima is considered in the case when two monochromatic light beams are incident on the crystal simultaneously. For each beam, double diffraction is realized, so that the propagation direction of one of the beams coincides with the propagation direction of the second-order diffracted ray for the other beam. It is shown that the diffraction pattern consists of three diffraction maxima: two of these are formed by the zero- and second-order diffracted rays, while the third maxima is formed by the first-order diffracted rays. The possibility of summation of the radiation intensities at the diffraction maxima is analyzed.     

平顶光束通过ABCD光学系统的传输

利用LI近期提出的平顶光束新模型,推导出平顶光束通过傍轴ABCD光学系统传输后光场分布的解析公式。以透镜系统为例,给出了平顶光束聚焦场分布的解析表达式,对平顶光束的聚焦特性进行了详细分析。     

非相干LED白光产生无衍射光的光源设计

非相干光源产生无衍射光束的实验中,入射光束的均匀性对产生无衍射光束的质量有很大影响。文中以非相干光源白光LED为例,通过对LED自身发光特性的分析,对光线传播过程进行数学建模,用非成像光学光通量守恒原理,对均匀照明设计方法进行理论推导,得到了一种基于非成像光学产生均匀光束的透镜设计方法。用三维建模软件进行建模并用光学仿真软件进行光线追迹,确定用该方法设计的透镜能满足实验对入射光束均匀度的要求,并初步实验获得较高质量的零阶无衍射Bessel光,验证了该设计方法的合理性。