移动式机动车激光测速仪的校准

针对移动式红外机动车激光测速仪的测量原理,详细描述了一种基于时间延迟的校准方法.采用虚拟仪器技术的机动车激光测速仪校准系统,能够将激光测速仪发射的905nm测量脉冲激光光束进行特定时间量的延迟以模拟其在空气中对应的传播距离,完成机动车激光测速仪在(20～250)km/h时速范围内任意速度值的实验室准确校准,模拟速度不确定度优于0.5%(k=2).     

激光测速仪的校准方法和装置

机动车超速自动检测系统的关键部分是机动车测速仪,包括线圈测速仪、多普勒雷达测速仪和激光测速仪三种类型.由于激光测速仪测速仪具备取证能力强、测速有效距离大(可达1Km)、测速准确度高(测误差<+1Km/h)、测量时间短、能测定车辆加速瞬间的速度等优点,受到了全世界广泛的认可和关注.     

机动车激光测速仪校准技术的研究

依据移动式(单光束)和固定式(双光束)红外机动车激光测速仪共同的测量原理,提出了一种基于时间延迟的校准方法.采用虚拟仪器技术的机动车激光测速仪校准系统,将激光测速仪发射的905nm测量脉冲激光光束进行特定时间量的延迟,以模拟其在空气中对应的传播距离,实现固定时间间隔激光脉冲串测量的距离变化量的精确模拟,完成机动车激光测速仪在20～250 km/h时速范围内任意速度值的实验室准确校准,其时间延迟分辨率为5 ps,对应位移分辨率为0.75 mm,模拟速度不确定度优于0.5%(k=2).     

移动式机动车激光测速仪的校准

针对移动式红外机动车激光测速仪的测量原理,详细描述了一种基于时间延迟的校准方法。采用虚拟仪器技术的机动车激光测速仪校准系统,能够将激光测速仪发射的905nm测量脉冲激光光束进行特定时间量的延迟以模拟其在空气中对应的传播距离,完成机动车激光测速仪在(20~250)km/h时速范围内任意速度值的实验室准确校准,模拟速度不确定度优于0.5%(k=2)。     

纳秒脉冲激光对316L不锈钢微抛光效果的影响

激光微抛光过程中,激光的能量密度对微抛光效果的影响很大.采用纳秒紫外脉冲激光(波长为355 nm,脉冲宽度为35 ns)对316L不锈钢材料进行微抛光实验研究,分析了工件表面的形貌、扫描速度和离焦距离等因素对激光微抛光效果的影响.通过对4种不同表面形貌的抛光效果比较,发现不仅表面粗糙度会影响抛光质量,而且表面的形貌也对激光微抛光的效果有很大影响;激光微抛光时对确定的激光能量密度存在最佳微抛光效果的扫描速度和离焦距离.提出了355 nm紫外纳秒脉冲激光器对316L不锈钢微抛光效果的最佳工艺参数:激光能量密度为0.14 J/cm2,激光脉冲重复频率为20 Hz,扫描速度为18.6 mm/min,离焦距离为81.2μm.在此工艺参数下,316L不锈钢经过微抛光之后,表面粗糙度由123.23 nm降低至80.96 nm.     

激光标靶位姿测量系统的建模与误差分析

针对大尺寸组合精密测量的需求,提出一种新型激光标靶位姿测量方法.首先介绍了其测量原理,并采用基于插值的非参数模型标定方法建立了入射光线姿态和相机靶面光斑的位置关系,通过基于参考棱镜的反向解算方法求解相机坐标系和激光标靶坐标系的位姿关系,构建了该测量系统的数学模型.基于此模型分析了测量系统的误差源,并对模型中影响测量结果的因素进行了仿真分析.最后通过实验进一步验证了模型的可行性和有效性.     

面向机器人标定的单激光跟踪仪顺序多站式测量系统建模与分析

为实现大型串联工业机器人的高精度标定,搭建了一种单激光跟踪仪的顺序多站式测量系统。该系统仅需单台激光跟踪仪,先后在不同的基站位置对工业机器人的末端位置进行独立测量,并基于多边测量方法计算机器人的末端位置。计算过程中仅需激光跟踪仪的距离信息,有效地优化了末端位置的测量不确定度。首先,建立了该测量系统的仿真模型,深入地分析了测量点的数量与分布形状、测量距离以及工业机器人定位精度等因素对系统测量精度的影响;然后,依据分析结果确定单激光跟踪仪顺序多站式测量系统的搭建方案。实验结果表明:该系统在2.5 m距离上的测量误差仅为0.023 mm,优于激光跟踪仪的测量精度,满足大型串联工业机器人参数标定的测量精度要求。     

高斯光束对零差测振系统光电信号的影响

结合高斯光束电场分布和平面波分析方法,推导了高斯光束照射下零差测振系统光电信号的解析表达式,分析了由高斯光束引起的相对测量误差.分别讨论了探测器与光传输轴线的距离,探测器与光腰的距离、振动位移、光腰半径与测量误差的关系.并对特定参数的零差测振系统进行了数值仿真,仿真结果与理论分析吻合.结果表明:振动住移和光腰半径与测量误差的关系比较复杂,测量误差随振动位移增加而增走的同时呈周期性波动;光腰半径与测量误差的关系曲线出现一零值点和一极大值点.为高精度激光测量误差分析提供了理论依据.     

热线风速仪微风速(0.1～1m/s)下的校准实验研究

热线风速仪在微风速(0. 1～1m/s)的测量中有广泛的应用,为了获得准确的测量结果,需要对热线风速仪进行校准。本文基于激光多普勒测速仪对热线风速仪的校准方法进行了研究,并在实验的基础上对恒温型热线风速仪的静态特性进行了分析。为了避免热线探针干扰流场对校准结果的影响,校准时需要找到激光多普勒测速仪合理的测量位置;实验段流场轴线上速度分布偏差带来的影响可通过激光多普勒测速仪的测量实现修正;采用防污染罩的方式可以避免粒子污染探针;此外,确定了2支热线风速仪的静态特性方程参数,计算结果表明实验与理论获得了良好的一致性。不确定度分析表明:在0. 1～1m/s的范围内,探针热线校准结果的不确定度为18mm/s左右。     

基于全站仪和激光跟踪仪的长距离标定方法研究

针对超长距离位置参数的高精度标定需求,设计了一种采用激光跟踪仪与全站仪的联合测量方法,该方法可集成两个系统各自优势满足测量需求.通过建立不同等级的测量控制网,采用分级测量技术,为全程测量提供基准,控制测量误差.采用统一空间测量网络的分析方法,将测量设备联合起来,建立统一的测量坐标系.结果表明,该方法可高精度、高效率的对...     

环形斑激光束在非线性克尔介质中的光束分裂效应

通过数值求解非线性Schrodinger方程,详细讨论了环形斑激光束在非线性克尔介质中的传输特性.当入射光超过一定功率时,光束产生多级自聚焦现象;传输过程中光束出现分裂现象,光束分裂的方式、分裂程度与入射光强度有关,并且光束分裂与自聚焦焦点处强度相联系.     

Dual-fiber collimator with elliptical spot for optical MEMS devices

Fiber collimators are widely used in optical communication components and fiber-optic sensors. Ordinary fiber collimators are made with a circular beam waist radius from 100?μm to 300?μm. The circular beam waist is too large to switch or shut the beam for certain micro-electro-mechanical system (MEMS) actuators (such as MEMS linear mirrors). In this paper, a dual-fiber collimator with an elliptical spot is proposed to meet the demands of MEMS optical devices. The elliptical spot collimator has been designed and fabricated, the beam waist spot of which is an elliptical spot with a 231.6?μm long-axis radius and a 12.87?μm short-axis radius, and its coupling loss is 0.37?dB.     

Determination of the longitudinal profile of a focused Nd:YAG Gaussian beam from second-harmonic generation in a thin KTP crystal

We present an original experiment describing a focused Gaussian laser beam by using second-harmonic generation (SHG) in a thin strip of a nonlinear optical material, in this case KTP doubling of an Nd:YAG laser at 1.064 μm. The dependence of the SHG efficiency on the fundamental beam radius allows the determination of beam parameters by harmonic-power measurements. The characterization of a telescope shows the good precision of this method in radii in the range of 10-100 μm. The average accuracy is 4% for the radius determination and 1.5% for the beam-waist localization.     

Mathematical model for laser densification of ceramic coating

A theoretical study for the densification of ceramic coating processed with a moving transmission electron microscopy (TEM00) mode laser beam is conducted. A three-dimensional quasi-steady state heat conduction model is developed by applying the Fourier integral transform method. An approximate expression for temperature distribution is also presented and the calculations with it are found to be in good agreement with the exact solutions within a limited region around the laser spot. The depth of the heat-affected zone in ZrO2 coating is calculated with this model. Moreover, a working range for ZrO2 densification is determined by varying the laser beam power, spot size and scanning velocity. The heat-affected zone is found to be confined within a depth of 50 μm from the surface and the vitrified layers are fully densified for particles of initial radius 5 μm. This revised version was published online in November 2006 with corrections to the Cover Date.     

Studies for Laser Densification of Ceramic Coating

A mathematical analysis describing the densification of ceramic coating processed with a moving TEM₀₀, mode laser beam has been presented in this paper. Calculations of the depth of the heat affected zone in ZrO₂, A1₂O₃ and TiO₂ ceramic substances is performed by adopting a three-dimensional quasi-steady state heat conduction model based on the mechanism of viscous solid-phase densification. Also, a working range for these ceramics coating densification is predicted by varying the laser beam power, spot size and scanning velocity. The heat-affected layer in ZrO₂ compact is found to be confined within a depth of 50 μm from the surface and it is fully densified for grains of initial radius 5 μm. A simple expression for temperature distribution is presented, which is found to provide sufficiently accurate estimates within a limited region around the laser spot.     

Laser ablation of silicon using a Bessel-like beam generated by a subwavelength annular aperture structure

Using a femtosecond laser incident to an oxide-metal-oxide film engraved with a subwavelength annular aperture (SAA) structure, we generated a Bessel-like beam to ablate silicon. Experimental results show that the silicon can be ablated with a 0.05 J/cm(2) input ablation threshold at 120 fs pulse duration. We obtained a surface hole possessing a diameter less than 1 μm. Optical performance, including depth-of-focus and focal spot of the SAA structure, were simulated using finite-different time-domain calculations. We found that a far-field laser beam propagating through a SAA structure possesses a submicrometer focal spot and high focus intensity. Our method can be easily adopted for surface machining in microfabrication applications.     

Noncontact Laser Inspection Based on a PSD for the Inner Surface of Minidiameter Pipes

A new noncontact laser-inspection technique based on a position-sensitive detector (PSD) to inspect the inner surface of minidiameter pipes is proposed, and the corresponding sensor is developed. A light spot is projected onto the pipe inner wall after the laser beam is reflected by two mirrors. At the same time, four current signals are produced when the light spot is read by the 2-D PSD. According to the magnitude of the current signals and the structure parameters of the sensor, the spot position on the inner wall can be calculated in a local 3-D coordinate system. With a micromotor, the surface of the whole inner wall can be scanned by the laser beam. This way, the coordinates of all the sample points in the section are obtained. After that, several reasonable data-processing methods are used, such as data segmentation and least squares fitting. Finally, the section curve can be reconstructed. The radius and defects of the section can also be obtained. Driven by a micropipe robot, the sensor can inspect a long curved pipe. The inspection system based on this technique can detect the inner surface of minidiameter pipes, which has an inner diameter of 9.5–10.5 mm and a curvature radius of more than 100 mm. The measurement accuracy of this inspection system for the inner diameter and surface defect reaches $pm$0.1 mm.      

Atomic structure display of a real silicon surface under light scattering

Angular dependencies of the scattered light intensity were measured on Si wafers that have different crystallographic orientations by using a He-Ne laser (λ = 632.8 nm, 80 μm spot diameter). During the experiment the Si wafer was fixed relative to the incident beam. Regular patterns were found in the azimuthal-angle-resolved scattering curves. Such patterns seem to be caused by the faceted shallow atomic structures of the surface.     

Microlenses and Microlens Arrays Formed on a Glass Plate by Use of a CO(2) Laser

Microlenses and microlens arrays were formed directly on a surface of a glass plate by use of a CO(2) laser. When the surface of a glass plate is heated locally to a working point of the glass material by use of a focused CO(2) laser beam, it tends to become a hyperboloid owing to surface tension, which results in a microlens. A profile of the microlens was measured with an ultrahigh accurate three-dimensional profilometer (Model UA3P, Matsusita Electric Industrial Company Ltd.) that utilizes a specially designed atomic force microscope. An intensity profile and a spot diameter at the focus of the microlens were measured with a microscope and a CCD system utilizing a He-Ne laser as a light source. The focused spot FWHM diameter of 1.35 mum was obtained, and the modulation transfer function was derived from the spot profile. Microlens arrays were also fabricated and characterized.     

Dependence of transverse and longitudinal resolutions on incident Gaussian beam widths in the illumination part of optical scanning microscopy

We studied both theoretically and experimentally the intensity distribution of a Gaussian laser beam when it was focused by an objective lens with its numerical aperture up to 0.95. Approximate formulas for full width at half-maximum (FWHM) of the intensity distribution at focus were derived for very large and very small initial beam waists with respect to the entrance pupil radius of the objective lens. In experiments, the energy flux through a 0.5 microm pinhole was measured for various pinhole positions. It was found in theoretical analysis and confirmed in experiments that the FWHMs at focus in the transverse and longitudinal directions do not increase much from the ultimate FWHMs until the input beam waist is reduced below half of the entrance pupil radius.