基于电压影响下圆偏振激光束的特性

采用狭缝光束分析仪和偏振仪测量了从铝薄膜表面反射的圆偏振光的光斑位置和偏振特性随外界直流电压变化情况,理论拟合激光从铝薄膜反射后的光斑位置与直流电流电压的关系。测量和多项式拟合结果表明,当外部电压值从0变化到2.5V时,圆偏振激光在x轴和y轴上的位置分别是从-45μm移动到-95μm,从35μm移动到75μm,而激光束的光学偏振度基本上不变化。     

Ablation of copper by a scanning Gaussian beam of a femtosecond laser pulse

This study investigated ablation from a copper metal surface using a scanning femtosecond laser beam with a Gaussian beam profile. A method was developed herein to calculate the ablation profile with experimentally identified parameters (e.g., effective focused Gaussian incident beam radius, ablation threshold fluence, effective energy penetration depth). The results show the relationship between the maximum ablation depth and maximum ablation width. The calculated ablation profile agrees well with the experimental measurements.     

平滑化窄脉冲高功率准分子激光放大技术

对于高功率准分子激光,光学角多路和诱导空间非相干(EFISI)光束平滑是高功率准分子激光压缩脉宽、提高功率密度和实现靶面均匀辐照的有效途径,其应用涉及前端至靶前的各个环节,主要体现为平滑化窄脉冲激光的传输放大问题.首先介绍了基于散射法开展的部分相千源前端技术及脉冲整形的初步研究结果,利用直接法和反射率耦合方法,研究了5...     

Thermal stresses due to time exponentially decaying laser pulse: elasto-plastic wave propagations

In the present study, thermal stress developed in the substrate material, which is subjected to a laser heating pulse is formulated. The closed form solutions for the temperature and stress fields due to time exponentially decaying laser pulse are presented. The Laplace transformation method is employed when deriving the governing equations. The elastic and plastic propagation of the stress waves are considered and the depth of the plastic zone is predicted. In order to account for the recoil pressure generated during the evaporation process, stress boundary at the free surface of the workpiece is considered. It is found that the magnitude of stress wave, due to stress boundary at the surface, well exceeds the elastic limit of the substrate material. Once the magnitude of the recoil pressure reduces considerably, elastic wave is generated. This occurs after t^*=0.032. Since the elastic wave propagates faster than the plastic wave, both waves meet at some depth below the surface. This, in turn, defines the depth of the plastic zone. In the present case, the depth of elastic zone extends to about x^*=9.2 below the surface. The magnitude of the stress wave generated due to temperature gradient is less than the yield strength of the substrate material; in which case, its magnitude decreases with increasing depth from the surface.     

基于光锥扩束机理的单脉冲激光近程静态探测方法

针对激光近程全向探测问题,在激光近程动态周向扫描探测机理研究基础上,提出了基于光锥扩束机理的单脉冲激光 近程静态周向探测方法。 基于激光近场探测理论和静态探测场空间几何分布,推导出基于光锥扩束机理的单脉冲激光近程静 态探测回波方程。 构建了单脉冲激光近程测距概率分布模型并搭建了实验室静态探测实验平台,研究了脉冲激光发射功率、倒 置反射光锥角、脉冲激光束发散角和目标尺寸投影面积对激光近程周向探测概率分布的影响机制。 结果表明:随着发射功率和 目标投影尺寸分别从 10 W 和 0. 01 m 2 增加到 30 W 和 0. 25 m 2 ,回波信号幅值亦随之从 0. 16 和 0. 43 μV 提升到 4. 22 和 5. 95 μV,随着倒置反射光锥角和光束发散角分别从 30° 和 10 mrad 增加到 120° 和 30 mrad,回波信号幅值随之从 3. 18 和 2. 52 μV 降低到 0. 88 和 1. 92 μV;周向探测概率分布随着发射功率和目标投影尺寸的增加而半宽减小且峰值增加并向左偏离、 随着倒置反射光锥角和光束发散角的增加半宽增大且峰值降低并向右偏离;探测分布对称性并不受以上 4 种因素影响。     

激光光束质量的评价与应用分析

从M²因子概念出发,分析了M²因子的概念与激光本质参数之间的关系,以及几种典型光束的M²因子,研究了M²因子的局限性,比较了针对不同应用目的的常用激光束质量定义的适用范围,探讨了激光光束质量的影响因素及其控制措施.     

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.     

Surface analysis of laser cladded Stellite exposed to self-mated high load dry sliding

Materials from the Stellite family of Co-based alloys are commonly used as low friction, galling resistant materials in high load dry sliding contact applications.In the present investigation, the surface region of a Co-based material (Stellite 21) exposed to self-mated high load dry sliding at room temperature has been analysed in detail.During sliding, an approximately 30 nm thick Co-enriched tribofilm is created. It exhibits low friction properties and a high galling resistance. The transformation from an face-centred-cubic structure to easily sheared hexagonal-closed-packed basal planes in the tribofilm combined with the high load carrying capacity of the underlying deformation hardened zone is suggested to explain the excellent low friction properties and galling resistance of this material.     

A study of beam position diagnostics using beam-excited dipole modes in third harmonic superconducting accelerating cavities at a free-electron laser

We investigate the feasibility of beam position diagnostics using higher order mode (HOM) signals excited by an electron beam in the third harmonic 3.9 GHz superconducting accelerating cavities at FLASH. After careful theoretical and experimental assessment of the HOM spectrum, three modal choices have been narrowed down to fulfill different diagnostics requirements. These are localized dipole beam-pipe modes, trapped cavity modes from the fifth dipole band, and propagating modes from the first two dipole bands. These modes are treated with various data analysis techniques: modal identification, direct linear regression (DLR), and singular value decomposition (SVD). Promising options for beam diagnostics are found from all three modal choices. This constitutes the first prediction, subsequently confirmed by experiments, of trapped HOMs in third harmonic cavities, and also the first direct comparison of DLR and SVD in the analysis of HOM-based beam diagnostics.     

Techniques trend analysis of propagating laser beam quality measurement

Different methods of measuring a propagating laser beam quality are summarized.The disadvantages in traditional way in measuring a laser beam quality is analyzed and the insufficiencies of the Shack-Hartmannin method which is commonly using wave front technique at present is pointed out.Finally,the transmission intensity equation based(TIE-based)measuring way in a laser beam quality evaluation and the corresponding advantages are discussed,which is believed to be a deve-l oping trend in laser beam evaluation.     

Low temperature laser scanning microscopy of a superconducting radio-frequency cavity

An apparatus was developed to obtain, for the first time, 2D maps of the surface resistance of the inner surface of an operating superconducting radio-frequency niobium cavity by a low-temperature laser scanning microscopy technique. This allows identifying non-uniformities of the surface resistance with a spatial resolution of about 2.4 mm and surface resistance resolution of ~1 μΩ at 3.3 GHz. A signal-to-noise ratio of about 10 dB was obtained with 240 mW laser power and 1 Hz modulation frequency. The various components of the apparatus, the experimental procedure and results are discussed in detail in this contribution.     

Focusing quality of a split short laser pulse

For multiple laser pulse experiments, it is necessary to split a laser pulse. In order to split a short laser pulse without stretching the pulse width, the laser pulse should not pass through thick materials. For this reason, a pellicle beam splitter (BS) and/or a mirror with a hole are required as a BS for the short laser pulse. The focusing qualities of the laser pulse after passing through the pellicle BS and the mirror with a hole are the same as without the BS's. The laser pulse quality reflected by the BSs should be considered for the laser pulse. A pellicle BS is a thin foil, so, it is weak against vibrations. One should be careful about airflows and isolation from vibration sources. The spot size of the reflected laser pulse is consistent with the size reflected by a normal mirror. The energy loss is about 10% compared with a normal mirror. A mirror with a hole is strong against external vibrations. The reflected laser pulse has a doughnut shape. The reflected laser pulse is interfered due to the shape. In order to cleanly focus the laser pulse, the inside size of the doughnut should be smaller than a half size of the outside portion of the doughnut.     

基于FEA的高速龙门加工中心横梁部件的热态特性分析与优化

针对高速龙门五轴加工中心横梁部件的热力学性能分析,考虑到相关热源部件的生热速率与结合面参数对热态特性的影响,利用有限元分析(FEA)方法中的热力学性能分析和热力学结构耦合模块,建立了横梁部件的热力学耦合模型。分析了影响横梁部件热变形的主要构件和相应的温度场分布,进行了结构优化。实验测试数据的结果分析验证了所建立的耦合模型的有效性。通过热补偿试验,证明了横梁部件热结构优化的正确性。     

CO2 laser pulse shortening by laser ablation of a metal target

A repeatable and flexible technique for pulse shortening of laser pulses has been applied to transversely excited atmospheric (TEA) CO(2) laser pulses. The technique involves focusing the laser output onto a highly reflective metal target so that plasma is formed, which then operates as a shutter due to strong laser absorption and scattering. Precise control of the focused laser intensity allows for timing of the shutter so that different temporal portions of the pulse can be reflected from the target surface before plasma formation occurs. This type of shutter enables one to reduce the pulse duration down to ~2 ns and to remove the low power, long duration tails that are present in TEA CO(2) pulses. The transmitted energy is reduced as the pulse duration is decreased but the reflected power is ~10 MW for all pulse durations. A simple laser heating model verifies that the pulse shortening depends directly on the plasma formation time, which in turn is dependent on the applied laser intensity. It is envisaged that this plasma shutter will be used as a tool for pulse shaping in the search for laser pulse conditions to optimize conversion efficiency from laser energy to useable extreme ultraviolet (EUV) radiation for EUV source development.     

引信激光装定用脉冲半导体激光器电源设计

在引信激光装定系统中，针对引信装定信息时脉冲半导体激光器，电源激光频率可调（PFM）、功率可调（PPM）的要求，结合半导体激光器的工作特性，设计一种以单片机（MCU）为控制芯片，以晶体三极管与场效应管为窄脉冲驱动电路的大功率半导体激光器电源。同时为电源驱动电路设计了DC-DC变换器。其中，激光频率设置为连续可调，激光器的驱动电流6～30A连续可调。该电源已应用于引信激光装定系统中，通过仿真与实验验证，该激光器电源工作正常、性能稳定。     

基于电压矢量注入法的PMSM无传感器控制

针对贴面式永磁同步电机的无传感器控制在低速和静止时一直存在着转子位置难以检测和估算的问题,提出了一种新的无传感器控制策略,即根据定子铁芯的非线性磁化特性,采用电压矢量注入法(Voltage Vector Pulse Method),在电机开始运行时,由闭环自适应磁通观测器估算转子位置、速度,实现转子初始位置检测。最终,通过Matlab仿真和实验,验证了该方法的有效性。     

Study of a hollow laser beam for cladding

Laser cladding, as a promising manufacturing technology, has been widely used in industry for component recovery and surface modification. In this paper, a hollow laser beam was proposed to optimize the laser intensity distribution. A three-dimensional (3-D) finite element (FE) model was developed using ANSYS to investigate the thermal field in the clad deposited by a hollow laser beam. The thermal results, such as the temperature distribution and the cooling rate, were investigated. The effect of the hollow ratio between the inner and outer radius of the hollow beam on the molten pool shape was also studied. The temperature at the boundary of the molten pool was higher than at the center. A clad with a flat metallurgical bonding was formed. The microstructure in the clad was mainly consisted of fine dendrites except the large columnar structures along the bonding. The hardness distribution of the clad was associated with the grain size distribution and the dilution by the substrate. The molten pool was not able to be generated with a high hollow ratio, while overheated at the center with a low hollow ratio. Based on the comparison with the Gaussian laser beam, the hollow laser beam could effectively alleviate the overheating at the center of the clad.     

Dynamic responses and fuzzy control of a simply-supported beam subjected to a moving mass

This paper deals with the active vibration control of a simply-supported beam traversed by a moving mass using fuzzy control. Governing equations for dynamic responses of a beam under a moving mass are derived by Galerkin’s mode summation method, and the effect of forces (gravity force, Coliolis force, inertia force caused by the slope of the beam, transverse inertia force of the beam) due to the moving mass on the dynamic response of a beam is discussed. For the active control of dynamic deflection and vibration of a beam under the moving mass, the controller based on fuzzy logic is used and the experiments are conducted by VCM (voice coil motor) actuator to suppress the vibration of a beam. Through the numerical and experimental studies, the following conclusions were obtained. With increasing mass ratioy at a fixed velocity of the moving mass under the critical velocity, the position of moving mass at the maximum dynamic deflection moves to the right end of the beam. With increasing velocity of the moving mass at a fixed mass ratioy, the position of moving mass at the maximum dynamic deflection moves to the right end of the beam too. The numerical predictions of dynamic deflection of the beam have a good agreement with the experimental results. With the fuzzy control, more than 50% reductions of dynamic deflection and residual vibration of the tested beam under the moving mass are obtained.     

Laser diagnostics of the evolution of a carbon surface exposed to high-power laser pulses

A method of online diagnostics of the surface state of materials exposed to high-power laser pulses is presented. The evolution of a graphite surface was observed on a laser monitor directly during the action of laser radiation on this surface. A method for reconstructing the surface relief from an image obtained using the laser monitor has been developed. It allows determination of the qualitative (based on the rms deviation of the image brightness) and quantitative (based on the correlation coefficient) characteristics of the surface.     

Thermal analysis of randomly oriented carbon nanotube reinforced functionally graded timoshenko beam

The unique thermal properties of carbon nanotubes (CNT) are utilized to increase the use of functionally graded material (FGM) at higher temperatures which resulted in introduction of a new type of material called as functionally graded carbon nanotube-reinforced composites (FG-CNTRCs). To use the FG-CNTRCs at elevated temperatures, their thermal analysis is very important. In this context, this article presents the thermal analysis of a CNT based FG Timoshenko beam. Material properties distribution is assumed to vary along the thickness direction according to power law distribution and linear distributions. Finite difference method is implemented to find out the temperature distribution. Using first order shear deformation theory (FSDT), expressions for strains and stresses are obtained. The results are compared with temperature distribution according to power law. The effect of CNT distribution on strains and stresses is also observed. Based on these results important conclusions have been drawn.