High-precision detection of focal position on a curved surface for laser processing

A new technique for detecting the focal position of a curved surface provides several advantages both in research and industrial applications. The quality of patterns lasered on a roll surface is determined by the precision of the focus detection, and surfaces of the massive rolls used in laser fabrication can be difficult to adjust properly using conventional technologies. Here, a unique method for detecting the focal position of a curved surface based on the reflected profile of a laser beam is presented. The versatility of the proposed technique results from being able to adjust the laser beam based on changes in the shape and diameter of the beam spot when the specimen surface deviates from the focal plane. A theoretical model based on three-axis movement is proposed, and experimental setups are developed based on the model. Analysis of the obtained results enables high precision positioning of the specimen and identification of the focal point. Furthermore, the presented technique can be used to locate the focal point on any curved surface. Therefore, the theoretical model, analysis results, and focal detection method can be combined in an algorithm for a novel auto-focusing system that can be applied to laser processing of curved surfaces, such as fabricating microgrooves, or engraving roll surfaces in printed electronics.     

A New Method to Determine Adhesion of Cantilever Beams Using Beam Height Experimental Data

A new method for calculating the apparent work of adhesion of microfabricated cantilever beams is presented and validated. This technique, based on popular beam mechanics, directly utilizes interferometrically produced deflection experimental data. The data are analyzed based on an energy minimization approach along the lines of a previous methodology. However, the new technique differs in that it does not rely on a priori knowledge of the shape of cantilever beams to evaluate work of adhesion. In order to validate the new method, both synthetic and empirical cantilever beam data were examined. The results show that apparent work of adhesion values calculated using this method agree well with values determined using a technique previously developed and widely accepted.     

Estimating the Charged Particle Beam Parameters in View of the Space Charge Forces

A method for estimating the main parameters of a paraxial axially symmetric charged particle beam taking into account the contribution of space charge forces is described. This method is based on the general equation for a beam envelope. The data characterizing its convergence and stability for experimental errors are presented. The errors in determining the crossover position and the beam radius in the crossover do not exceed 15%, and the error in estimating the emittance depends on the relationship between the emittance and space charge forces. This method has been used to estimate the parameters of an actual electron gun with an energy of 50 keV and a current of 0.64 A. The results obtained are in good agreement with the design values. The technique described may be generalized to the case in which axial symmetry is absent.     

SiCp颗粒增强铝基复合材料非共线非线性响应试验观察

采用粉末冶金方法制备的碳化硅颗粒增强铝基复合材料(SiCp/Al)受加工过程工艺影响较易出现SiCp颗粒分布不均等缺陷。传统的金相法及声速扫描法检测该缺陷存在破坏试样及定位困难且灵敏度不高等问题;基于谐波的穿透式共线非线性无损检测方法检测灵敏度高,但易受到其他非线性试验来源的干扰。为解决这一问题,利用基于波束混叠的非共线非线性超声检测方法,观察SiCp/Al的非共线非线性响应,探讨使用该方法检测粉末铝基复合材料非均匀性缺陷的可行性;建立非共线非线性超声检测试验系统,发现LY12铝合金及SiCp/Al试样内部的波型转换与波束混叠现象;利用非共线技术的空间可达、波型转换及频率方向可控等性质,成功剔除了非线性的试验来源,从试验上证明该方法能够观测试样内部的非线性,具备检测SiCp/Al试样均匀性的潜力。试验方法与结果为进一步研究非共线混叠波与粉末铝基复合材料均匀性的相关关系及扫查方法奠定基础。     

Detecting surface and volume defects in metals by the laser-acoustic method

An all-purpose non-destructive method for detecting surface and volume defects in metallic objects has been developed. This technique is based on scanning the surface of a studied object with a focused laser beam and detecting the generated acoustic waves with a piezoelectric sensor. Defect control is performed by measuring the amplitude and propagation time of an acoustic signal to a detector, when the laser beam passes a defect zone.     

Transverse vibrations of an Euler–Bernoulli uniform beam carrying two particles in-span

Vibrations of beams carrying different combinations of particles, heavy bodies and spring-mass systems which are located on or off resilient supports have been tackled by several researchers. Most of the approaches were based mainly on various approximate methods. In this paper an analytical solution based on the classical beam eigenvalue technique is presented for the vibrations of a beam carrying two particles. For purpose of analysis, the beam was divided into a portion from one end to the first particle, a portion between particles and a portion from the second particle to the other end. The frequency equation is expressed in closed form as a 2nd order determinant equated to zero. Schemes are presented to compute the 4 elements of the determinant and to evaluate the roots of the frequency equation. Computational difficulties were not encountered in the implementation of the schemes. The first three natural frequency parameters are tabulated for 16 combinations of the classical boundary conditions and several combinations of the location and mass of the particles. The beam mode shape is the juxtaposition of the mode shapes of the three portions of the beam. Some examples of normalised beam mode shapes and location/s of node/s are also presented. The results may be used to judge the accuracy of values obtained by approximate methods.     

Analysis methodology of movable emittance-meter measurements for low energy electron beams

The design of photoinjectors for modern free electron laser linac relies heavily on particular beam behavior in the few meters after the gun. To experimentally characterize it a movable emittance meter was proposed and built [L. Catani et al., Rev. Sci. Instrum. 77, 093301 (2006)] based on the beam slicing technique. This paper addresses all the aspects of analysis of the data acquired with the emittance meter and common to any slit based emittance measurement for low energy beams.     

The elastic spring behavior of a rhombus frame constructed from non-prismatic beams under large deflection

The spring behavior due to large deflection of a flexible rhombus frame with rigid joints is studied in this paper. The system consists of two equal and opposite diagonal forces that act on two opposite corners of a rhombus frame with a given apex angle γ. The frame sides have a rectangular cross-section and are non-prismatic due to tapering in the section's dimensions. The relations between the large displacement at the corners and the applied forces are obtained using a new robust numerical technique. The technique is based on representing the angular deflection of the side beam by a polynomial on the position variable along the deflected beam axis. The polynomial coefficients are obtained through a numerical optimization procedure based on minimizing the residual error and satisfying the boundary conditions. A classical numerical integration technique is used to verify some of the results obtained by the proposed technique. The frame spring behavior is investigated for different taper ratios and apex angles. The results are transformed into regression relations to utilize its implementation in design and analysis.     

Investigation of range-energy relationships for low-energy electron beams in silicon and gallium nitride

The electron beam technique of the Scanning Electron Microscopy (SEM) has been widely used for the characterization of bipolar devices and photodiode materials. The resolution of an electron beam technique is affected by the interaction of the beam and the specimen. The size of this interaction volume, commonly termed the generation volume, is usually characterized by what is called the electron penetration range and is measured from the surface. Since there is currently no consensus on the expressions to use in the calculation of the electron range, this paper provides an analysis of the three most commonly used semiempirical expressions. They are the Gruen range, the universal curve of Everhart and Hoff, and the maximum range of Kanaya and Okayama. This analysis is done using data from the statistical method of Monte Carlo simulations. It was found that the Everhart and Hoff universal curve performs better at low beam energies than the equation of Kanaya and Okayama. However, the validity of all the three expressions is questionable below 5 keV. In order to overcome this, fitted expressions based on the extrapolated range are provided for beam energies below 5 keV in the case of Si and GaN materials. The accuracy of these expressions is affected by the physical parameters used in the Monte Carlo simulations.     

Setup for in situ deep level transient spectroscopy of semiconductors during swift heavy ion irradiation

A computerized system for in situ deep level characterization during irradiation in semiconductors has been set up and tested in the beam line for materials science studies of the 15 MV Pelletron accelerator at the Inter-University Accelerator Centre, New Delhi. This is a new facility for in situ irradiation-induced deep level studies, available in the beam line of an accelerator laboratory. It is based on the well-known deep level transient spectroscopy (DLTS) technique. High versatility for data manipulation is achieved through multifunction data acquisition card and LABVIEW. In situ DLTS studies of deep levels produced by impact of 100 MeV Si ions on Aun-Si(100) Schottky barrier diode are presented to illustrate performance of the automated DLTS facility in the beam line.     

Nanometer edge profile measurement of diamond cutting tools by atomic force microscope with optical alignment sensor

This paper describes an atomic force microscope (AFM) based instrument for nanometer edge profile measurements of diamond cutting tools. The instrument is combined with an AFM unit and an optical sensor for alignment of the AFM probe tip with the top of the diamond cutting tool edge in the submicrometer range. In the optical sensor, a laser beam from a laser diode is focused to generate a small beam spot with a diameter of approximately 10 μm at the beam waist, and then received by a photodiode. The tool edge top and the AFM probe tip are brought to the center of the beam waist, respectively, through monitoring the variation of the photodiode output. To reduce the influence of the electronic noise on the photodiode output so that the positioning resolution can be improved, a modulation technique is employed that modulates the photodiode output to an AC signal by driving the laser diode with a sinusoidal current. Alignment experiments and edge profile measurements are carried out.     

Improvements to differential voltage contrast and light and electron scanning beam analysis of solar cells

Differential voltage contrast (DVC) in conjunction with light and electron beam scanning (LEBEAMS) technique were used for measuring the electric potential, field, and charge distribution in solar cells. The DVC is based on enhancement or retardation of secondary electron emission, generated by an electron beam, due to local changes in the potential of a semiconductor device. The information provided by this technique is invaluable to the development of any device. Solar cells have been studied by the DVC technique, both under electrical bias (DVC) and under illumination (DVC in conjunction with LEBEAMS); however, the conditions of the previous did not replicate the normal illumination conditions of a solar cell. The goal of this research was to redesign and expand the previous LEBEAMS experiments to produce accurate profiles of quasi Fermi energies on solar cells.     

Applying an On-line Crack Detection Technique For Laser Cutting by Controlled Fracture

A new laser cutting system, which uses a laser to induce controlled fracture and combines an image processing technique for crack detection and compensation of the laser path to control crack direction, is proposed in this study. The laser cutting is based on the controlled fracture technique, the laser beam strikes the surface of a thin brittle plate which results in a stable fracture. The cutting of the material results from crack propagation along the cutting path. Because the crack propagation at the crack tip is slower than the moving laser beam, the actual fracture trajectory will deviate from the desired trajectory, for example, when cutting a curve or a right angle, especially at high cutting speed. In order to eliminate the deviation, the actual position of the crack tip must be detected on-line and the path of the laser beam must be modified. The compensation is based on the lagging distance between the crack tip and the laser spot. The laser cutting system comprises a CO2 laser, a digital image-processing system, and an XYZ positioning table. The cutting of right angles for silicon wafers and the cutting of circular arcs for alumina ceramics are carried out to validate the system. The image processing speed of the crack detection system is 0.1 s per detection, which is fast enough for continuous on-line crack detection, so that the method can be applied for any complicated curve cutting.     

Development of a new analytical electron microscopy technique to quantify the chemistry of planar defects and to measure accurately solute segregation to grain boundaries

A new technique of analytical transmission electron microscopy called ConceptEM has been developed for determining highly accurately small amounts of solute or dopant atoms incorporated into well‐defined planar defects such as stacking faults, grain boundaries or interfaces. The method is based on recording series of analytical spectra taken with different electron beam diameters on the same position centred above a defect that is orientated either edge‐on or slightly inclined with respect to the electron beam. It can be applied to energy‐dispersive X‐ray spectroscopy or electron energy‐loss spectroscopy and necessitates only a nano‐probe modus but no scanning unit. Reliability and accuracy have been tested numerically under various conditions using simulations for a specific geometry, as a function of specimen thickness, material, acceleration voltage, collection angle, random beam displacements and solid solubility. The accuracy has been found to be substantially better (by factors of 5–10) than that of any other current standard technique based on single measurements. Our calculations suggest an accuracy in the determination of the Gibbsian solute excess at a special grain boundary down to ±1% of a monolayer, i.e. around ±0.1 atoms nm^?2 under typical experimental conditions, with a maximum error about twice as large. The parameter limiting a straightforward analysis is found to be the solid solubility, which itself, however, can be measured accurately by the technique so that it can be taken into account quantitatively and the above‐stated precision is retained.     

Upgrade of the lithium beam diagnostic at JET

A 60 kV neutral Li beam is injected into the edge plasma of JET to measure the electron density. The beam observation system has been improved by replacing a Czerny-Turner spectrometer with a high-resolution transmission-grating spectrometer and a fast back-illuminated frame-transfer camera. The larger throughput of the spectrometer, the increased sensitivity, and the faster readout of the new camera allow inter-ELM (edge localized mode) measurements (frame rate of 100 Hz). The calibration of the setup, as well as an improved spectral fitting technique in the presence of carbon background radiation, is discussed in detail. The density calculation is based on a statistical analysis method. Results are presented for different plasma scenarios.     

A Practical method for determining the beam profile near the focal spot

In laser material processing, knowledge of the beam profile and beam diameter are fundamental in achieving acceptable results. The beam profile is affected by errors in the focusing optics, namely spherical aberration. This causes the minimum beam diameter to be larger than that predicted by beam propagation equations. Current methods of beam profiling use electronic equipment to measure the relative intensity of the beam at different locations along the beam, which is time consuming and involves high cost. Furthermore, the measurement near the focus spot usually is not feasible, due to excessive power density in this region. A novel one-step technique is developed to determine the beam profile near the minimum spot and the associated effect of spherical aberration. The effect of spherical aberration on the beam profile is investigated for three plano-convex lenses and compared to the ideal beam profile based on the beam propagation model. It was found that the technique is useful in determining the beam profile without using expensive equipment. It was also found that using a beam expander in conjunction with a focusing lens introduced errors in the form of spherical aberration that caused the diameter of the laser beam to increase as well as the beam quality. Removing the beam expander removed the spherical aberration effect, but the beam diameters were increased because of decreased focusing ability.     

Charge breeding simulations for radioactive ion beam production

The charge breeding technique is used for radioactive ion beam (RIB) production in order of optimizing the re-acceleration of the radioactive element ions produced by a primary beam in a thick target. Charge breeding is achieved by means of a device capable of increasing the ion charge state from 1+ to a desired value n+. In order to get high intensity RIB, experiments with charge breeding of very high efficiency could be required. To reach this goal, the charge breeding simulation could help to optimize the high charge state production efficiency by finding more proper parameters for the radioactive 1+ ions. In this paper a device based on an electron beam ion source (EBIS) is considered. In order to study that problem, a code already developed for studying the ion selective containment in an EBIS with RF quadrupoles, BRICTEST, has been modified to simulate the ion charge state breeding rate for different 1+ ion injection conditions. Particularly, the charge breeding simulations for an EBIS with a hollow electron beam have been studied.     

Improvement of damage detection methods based on experimental modal parameters

The objective of this paper is to introduce a new method for structural damage detection based on experimentally obtained modal parameters. The new method is suitable for detection of fatigue damage occurring in an aluminium cantilever beam. The damage has been practically realised as saw cuts of different sizes and at different locations. The first step of analysis included an attempt of damage identification with the most often used damage indicators based on measured modal parameters. For that purpose special signal processing technique has been proposed improving the effectiveness of indicators tested. However the results obtained have not been satisfactory. That was the motivation for defining new damage indicators (frequency change based damage indicator, Hybrid Damage Detection method), utilising the change of natural frequencies and any mode shape (measured or modelled) as the measurement of frequencies is much less time consuming in comparison to total mode shape measurement. It has been shown that the proposed technique is suitable for damage localisation in beam-like structures.     

Wave transmission at discontinuities using wavenumber-frequency techniques

The problem of wave transmission between two finite beams joined by a cross beam welded between them is solved taking full account of longitudinal and flexural waves in all the beams. Prediction of longitudinal and flexural wave transmission through the “T” joints in the beam system was performed over a wide band frequency range. The wavenumber-frequency spectrum was used to separate the wave types based on their different dispersive characteristics. Flexural direction forces at one end of the beam system were examined. The experimental data were taken using an accelerometer array and a simultaneous twenty-three channel measuring system. A transfer function correction technique was employed to account for the instrumentation errors. Experimental results were confirmed by the finite element analysis results. The total mean squared vibrational energy levels were calculated in each section of the beam system to quantify the transmission characteristics of both flexural and longitudinal waves passing through the beam joints.     

Optical detection of cell-surface changes associated with malignant transformations in vitro.

A need exists for new experimental approaches for the direct detection of cell-surface changes associated with malignant transformations. The usual methods of fractionating the cell to obtain plasma-membrane segments are disruptive and are influenced by uncertainties that frustrate most attempts to distinguish between the cell memebrane in the normal and malignant states. Here we describe a non-destructive microprobe technique using a light beam to monitor cell-surface changes in situ. Many investigations of tumor-cell behavior in culture are based on substrate-adherent populations of cells. By choosing the substrate to be optically dense and transparent, and by striking the substrate/cell interface by a light beam from the substrate side at an angle of incidence greater than the critical angle of total-internal reflection, an evanescent electromagnetic wave interacts with the peripheral zone of the substrate-adherent cells. Both the intensity and ellipse of polarization of the reflected wave can be monitored as the malignant transformation takes place, either chemically or virally. This technique should also provide new information concerning the molecular organization of the cell periphery from measurements on living cells.