3-D surface profilometry using simultaneous phase-shifting interferometry

Urgent needs for high-speed, non-contact and on-line measurement with high accuracy and repeatability are of great interest for automatic optical inspection (AOI) industries. Therefore, optical phase-shifting interferometry for precision 3-D surface profilometry has become an important metrological method due to its non-contact and high measurement accuracy. Traditional phase-shifting interferometry is very sensitive to vibrations because image acquisition in various phase-shifting sequences could easily introduce measurement errors from environmental influences, such as air disturbance and system structure vibrations. In this paper, we introduce a new simultaneous phase-shifting interferometer for 3-D surface profilometry which employs a single glass plate to generate simultaneous phase-shifted interferograms. Phase reconstruction is performed by using a developed phase-shifting algorithm which uses a three-step phase-shifting method with phase differences of 90°, 180°, and 270° for three interferograms. To verify measurement accuracy and repeatability, the system was employed to measure surface profiles of surface of a flat mirror and set of Mitutoyo gauge blocks. The experiment result shows that the method is proven to be capable of performing one-shot interferometric measurement and minimizing influences from environmental disturbances with measurement repeatability down to 10 nm or less.     

Static and dynamic detection of axial surface defects on metallic wires by conical triple laser reflection

The quality of the surface of metallic wires is relevant for different applications. The reflection of a laser beam on the surface of a metallic cylindrical wire provides an efficient way to inspect the quality of its surface. Our interest is focused in the detection of axially oriented defects, which are the most relevant for the wire drawing process. We present a simple interference-geometrical model to describe the light pattern reflected from a wire with defects. This model adequately accounts for the observed results from an industrial prototype developed for the purpose. It incorporates three-laser beams incident on the wire at equidistant locations in its perimeter, which produce three reflection cones with a CCD. This configuration permits to explore the whole perimeter of the wire. Several results are presented, both in static operation and in production line, in agreement with qualitative and quantitative predictions.     

飞秒激光烧蚀硅材料表面形成周期波纹形貌研究

基于Sipe-Drude模型和表面等离子体激元(SPP)的干涉理论分别对单脉冲飞秒激光诱导硅表面形成低频率周期性波纹进行分析研究.探究了波长800 nm、脉宽150 fs的单个飞秒激光烧蚀硅造成不同激发水平下波纹形貌的变化,考虑到材料的光学性质变化(由Drude模型得到的介电常数变化),引入包含双温方程的电子数密度模型.计算结果表明,Sipe-Drude和SPP理论都适用于分析和解释高激发态下周期性波纹,但Sipe-Drude理论更适合分析更为广泛的周期性波纹结构.同时,波纹延伸方向总是垂直于入射激光偏振方向,其空间周期略小于激光波长,并受到入射激光通量的影响.在激光通量为0.38 J/cm~2时,波纹周期达到最小值.另外,还得到了不同入射角度的波纹周期变化情况,并在不同偏振态下随入射角度增大时波纹周期呈现相反的变化趋势.该研究对于理解飞秒激光造成硅表面形成周期结构及其在加工硅材料领域具有重要参考意义.     

飞秒激光诱导钛表面形成高空间频率周期条纹结构

利用波长为800 nm的飞秒激光,在空气和去离子水中诱导钛表面形成不同的周期条纹结构。在空气中,激光能量密度为0.265 J/cm2时,钛表面主要形成周期为500~560 nm低空间频率条纹结构;激光能量密度为0.102 J/cm2时,主要形成的是周期为220~340 nm高空间频率条纹结构。两种条纹均垂直于入射激光偏振方向,且条纹周期随着脉冲重叠数的增大而增大。在水中,除形成垂直激光偏振方向、周期为215~250 nm的高空间频率条纹结构,还形成了平行于激光偏振方向且周期约为入射激光波长八分之一的高空间频率条纹结构。利用表面等离子体理论、二次谐波及Sipe理论对各种周期条纹结构的形成机理进行分析,发现周期条纹结构的形成与钛表面氧化层有密切的关系。     

Study of some surface properties using a simple gradient expansion of the kinetic energy density functional

Summary Reasonable surface energies and very accurate surface dipole barrier and work function for a semi-infinite jellium are calculated from a simple model of the density. The model was proposed by Smith and contains one universal parameter. In the Kohn-Sham energy functional, the kinetic energy is approximated by its simple gradient expansion including a fourth-order term. The exchange and correlation are treated within the local-density approximation. Using the simple gradient, the energy is minimized with respect to the universal parameter of the density. The parameter which minimizes the energy is used to calculate the surface dipole barrier and the work function. A comparison was made with the Lang and Kohn results and with the Ma and Sahni results.     

超短脉冲激光诱导周期性表面结构

激光诱导周期性表面结构（Laser-induced periodic surface structures,LIPSS）具有纳米尺度的特征结构和自重复的微观尺度的排列图案,因此,LIPSS在传感器、太阳能发电、光催化等方面具有广泛的应用前景。本文首先介绍LIPSS形成过程中超快激光与物质相互作用的复杂过程,强调瞬态光学性质和表面结构变化的作用。然后综述几种具有代表性的LIPSS形成机理,并且讨论了各自的优缺点。接着介绍了LIPSS形成过程中材料的变化,主要包括材料化学成分、晶体结构和表面微观结构的变化。最后综述了LIPSS在材料表面处理、光学和机械等方面的应用。     

Metal surface coloration by oxide periodic structures formed with nanosecond laser pulses

In this work, we studied a method of laser-induced coloration of metals, where small-scale spatially periodic structures play a key role in the process of color formation. The formation of such structures on a surface of AISI 304 stainless steel was demonstrated for the 1.06 µm fiber laser with nanosecond duration of pulses and random (elliptical) polarization. The color of the surface depends on the period, height and orientation of periodic surface structures. Adjustment of the polarization of the laser radiation or change of laser incidence angle can be used to control the orientation of the structures. The formation of markings that change their color under the different viewing angles becomes possible. The potential application of the method is metal product protection against falsification.     

激光照明水下目标距离选通成像系统的研制

基于水下目标探测的应用需求,研制开发了一套激光水下距离选通成像系统。系统采用波长532 nm、最大单脉冲能量400 mJ的Nd:YAG脉冲激光器作为照明光源,采用最小选通门宽3 ns、像元10241024的ICCD相机作为门选通器件和图像记录器件,利用DG535型数字脉冲发生器作为精确延时和同步控制器件实现激光脉冲和ICCD相机选通门的同步以实现距离选通功能。利用该系统在某水库进行了水下目标探测实验,实验结果表明,该系统可在6.5倍的衰减长度上识别目标,在8倍衰减长度上发现目标。     

Review of surface profile measurement techniques based on optical interferometry

With the fast development of modern science and technology, two or three-dimensional surface profile measurement techniques with high resolution and large dynamic range are urgently required. Among them, the techniques based on optical interferometry have been widely used for their good properties of non-contact, high resolution, large dynamic measurement range and well-defined traceability route to the definition of meter. A review focused on surface profile measurement techniques of optical interferometry is introduced in this paper with a detailed classification sorted by operating principles. Examples in each category are discussed and analyzed for better understanding.     

激光照明水下目标距离选通成像系统的研制

基于水下目标探测的应用需求,研制开发了一套激光水下距离选通成像系统。系统采用波长532 nm、最大单脉冲能量400 mJ的Nd:YAG脉冲激光器作为照明光源,采用最小选通门宽3 ns、像元10241024的ICCD相机作为门选通器件和图像记录器件,利用DG535型数字脉冲发生器作为精确延时和同步控制器件实现激光脉冲和ICCD相机选通门的同步以实现距离选通功能。利用该系统在某水库进行了水下目标探测实验,实验结果表明,该系统可在6.5倍的衰减长度上识别目标,在8倍衰减长度上发现目标。     

Holographic contour mapping using a dye laser

Narrow depth contour lines with variable depth distance were generated, using a multiple-frequency cw-dye laser. The feasibility of extending contour mapping with dye lasers to very large objects is discussed.     

Motion imaging of objects in layers hidden by scattering media using low-coherence speckle interferometry

A novel method is proposed for motion imaging of objects in layers hidden by a scattering medium in a depth-resolved manner by means of the intensity difference in a temporal sequence of low-coherence speckle images. Depth-resolved motion imaging was demonstrated with a semi-transparent scattering plate and an aluminum diffusive plate behind Intralipid solution. Experimental results confirmed feasibility of the proposed method for imaging of moving objects by their relative velocity.     

低频水下声信号的激光探测

根据表面波声光效应的原理,提出了一种低频水下声信号的激光探测技术,并建立了实验装置。在几十赫兹的低频段,对水下声源所产生的表面声波进行了探测。实验过程中,利用MATLAB软件对拍摄的衍射图样进行扫描分析,得到了衍射图样中条纹的像素差。根据波长与条纹间距的解析关系式,得到了低频液体表面声波波长,其大小在毫米量级。利用计算机编程,根据最小二乘法拟合色散关系的回归曲线,测量结果与理论色散关系吻合。该方法具有实时、非接触的特点。     

Quantitative visualization of the laser induced plume behavior using quasi-heterodyne holographic interferometry

It is very important that we understand the dynamic behaviors of the laser induced plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. Many experimental studies have been performed in order to observe the plume behaviors using a visualization method. In this paper, we describe the visualization and quantification of the laser induced plumes by pulse holographic interferometry. A pulsed Nd:YAG laser was used for the generation of laser induced plume and a Q-switched Ruby laser was employed to record the weld plume. For qualitative visualization of the laser induced plume, we used the double-exposure holographic interferometry. Then, we chose the quasi-heterodyne holographic interferometry with the dual-reference-beam and phase shifting in order to visualize the plume quantitatively. The experimental results show the visible behavior of the laser induced plume according to a change in the output power of the pulsed Nd:YAG laser and the time delay of Q-switched Ruby laser. Finally, we obtained the quantitative results by using the dual-reference-beam.     

Planar surface reconstruction using circle generator laser light

A method is presented for finding the spatial position and orientation of a planar surface using a laser light source that generates structured light in the form of concentric circles. The purpose of the work is to provide the foundation for mapping regular and irregular surfaces for use in spatial surface reconstruction. The results of this work will lead to practical applications in the evaluation of pre- and post-surface deformation, and the reconstruction and representation of higher ordered surfaces. The latter having application as an alternative approach for capturing surfaces in direct geometric terms as opposed to the copious data discretization methods employed in surface reconstruction today.     

基于合作目标的激光水下定位

为了准确获取水下运动目标的运动轨迹,提高测量的数据率,提出了一种基于合作目标的激光水下定位方法。通过在被测目标上加装合作目标,利用合作目标的全反射特性,实现了脉冲式激光水下测角与测距的功能。介绍了激光水下定位的方法和系统组成,给出了水下定位的数学模型及测量结果。模拟实验结果表明,该方法具有一定的工程应用价值。最后,结合工程应用,对激光水下定位需要解决的一些实际问题进行了分析。      

单脉冲纳秒激光诱导硅表面微结构

利用Nd:YAG纳秒脉冲激光(波长532 nm)在空气中对单晶硅表面进行单脉冲辐照,研究了激光能量密度和光斑面积变化对微结构的影响。通过场发射扫描电子显微镜和原子力显微镜(AFM)对样品表征,并对纳秒激光辐照硅的热力学过程进行分析。结果显示：当脉冲激光的能量密度接近硅的熔融阈值且光斑直径小于8 m时,形成尖峰微结构;随着能量密度或光斑面积增大,尖峰结构消失,形成边缘隆起和弹坑微结构。通过流体动力学模型得到微结构形貌的解析解,模拟得到的微结构形貌与实验测得的AFM数据一致。研究表明微结构的形成主要是由于表面张力引起的熔融硅流动。表面张力与表面温度和表面活性剂的质量浓度有关。温度梯度引起的热毛细流作用和表面活性剂浓度引起的毛细作用共同影响下形成尖峰、边缘隆起和弹坑微结构。     

前向散射对激光水下成像的影响

为研究前向散射对水下成像的影响,利用辐射传输理论建立了激光水下成像前向散射理论模型,提出了水下成像前向散射影响系数,用以表征前向散射对水下成像质量的影响程度,并给出了前向散射功率及前向散射影响系数的解析表达式。利用Matlab进行了数值模拟分析,得出了水下成像前向散射光功率和影响系数随探测水深及水衰减系数的变化规律,说明了非对称因子的取值对成像质量具有较大的影响。     

前向散射对激光水下成像的影响

为研究前向散射对水下成像的影响,利用辐射传输理论建立了激光水下成像前向散射理论模型,提出了水下成像前向散射影响系数,用以表征前向散射对水下成像质量的影响程度,并给出了前向散射功率及前向散射影响系数的解析表达式。利用Matlab进行了数值模拟分析,得出了水下成像前向散射光功率和影响系数随探测水深及水衰减系数的变化规律,说明了非对称因子的取值对成像质量具有较大的影响。