剪切散斑干涉技术及应用研究进展

剪切散斑干涉技术是一种非接触测量物体变形缺陷的光学无损测量方法,其通过计算物体变形前后的散斑图中的相位获取被测物的应变缺陷信息。近年来该技术在航空、航天等工业无损检测领域得到了广泛的应用。本文从系统关键技术、散斑图像处理技术两方面介绍了剪切散斑干涉技术的研究进展,详细论述了多种剪切装置实现大视角测量、空间载波实现动态测量、多种图像处理算法的一系列剪切散斑干涉技术;最后介绍了剪切散斑干涉技术的国内外应用进展,展望了剪切散斑干涉技术在动态测量、光滑表面测量及定量反算形变量等方面的发展趋势。     

马赫曾德双成像的镜面材料内部缺陷检测系统

针对传统剪切散斑干涉技术只能测量粗糙表面,无法直接测量镜面物体的缺陷,提出了一种改进的剪切成像装置,利用被测物表面反射由激光经毛玻璃组扩束后产生的散斑来实现镜面物体缺陷检测;同时采用双成像的马赫曾德干涉系统,实现剪切量与载波频率的独立调整,扩大有效测量区域.对8k镜面板采用顶针加载的方式,对预置缺陷的镜面表面材料采用热加载的方式,进行缺陷检测.实验结果表明:该方法检测出的缺陷分布与加载方式、预置缺陷的分布基本保持一致,可实现对镜面材料内部缺陷的快速动态检测.     

基于单幅数字散斑投影及图像相关的离面振动测量

采用单幅数字散斑图投影及高速数字图像采集技术,研究了动态离面位移的测量。采用商用液晶投影仪将计算机产生的模拟散斑图投影到待测动态变形物体表面,由高速数字图像采集设备摄取并保存变形散斑图,采用时间序列数字图像相关软件计算出物体表面各点随时间变化的离面位移。这种方法用于振动分析时不仅可以获得振型分布,而且还可以获得各点的振幅值。与现有的激光频闪照相测振及激光多普勒测振等方法相比,具有光学系统简单,可全场定量测量。悬臂梁振动实验结果证实了该方法的有效性。     

基于散斑干涉的光滑表面变形快速检测

针对目前光滑表面力学性能测试困难的情况,建立了一种改进的数字激光散斑干涉测量系统。首先通过新的散斑干涉光路设计实现散斑照射,同时采用空间载波傅里叶变换法,对光滑零件加载变形的动态散斑干涉图像进行处理,最后得到光滑表面的变形场分布情况。该方法不对被测表面进行任何处理,可实现光滑表面的高精度全场变形测量。实验结果表明:最大变形处为镜面板的中央,测得最大变形量分别为1.936、1.861和1.797μm,与中心变形预设值接近。该方法光路简单、测量方案切实可行,能够实现光滑表面变形的快速动态测量。     

数字散斑干涉三维变形测量技术研究进展

三维变形可以转换为应力/应变分布，是材料性能测试和结构可靠性分析的关键参数。在众多三维变形测量技术中，数字散斑干涉技术可以高精度地测量三维变形信息，在航空航天、汽车、先进制造、土木工程和生物医学等行业发挥着十分重要的作用。从散斑干涉基本原理出发，详细介绍了几类三维变形散斑干涉测量技术，并分析比较各类方法的优缺点；同时介绍了散斑干涉三维变形测量技术的国内外研究进展和最新应用；最后展望了散斑干涉三维变形测量技术在动态同步测量、测量系统简化以及应用范围扩宽等方面的发展趋势。     

三维时域散斑动态干涉测量系统的集成化设计

三维电子散斑干涉技术（3D ESPI）具有非接触、高精度、高灵敏度和全场测量等优点，被广泛应用于许多领域。为了实现非接触动态全场三维测量，设计并建立了一个紧凑、完备的三维测量系统。用一个多波长光纤耦合激光器代替3个独立光源，产生的离面、面内散斑干涉图仅用一台彩色CCD相机就能捕捉和处理；整个测量系统采用笼式结构，具有高度的灵活性和稳定性；对基于小波变换的相位展开算法进行了编程，实现了被测物体三维位移信息的完整提取。实验证明该测量系统可以实时获取被测物体的三维位移，在测量实验中，获得的三维位移值17.68 μm、36.23 μm、13.85 μm，相比于实际位移值18.1 μm、36.4 μm、14.0 μm它们的绝对误差分别为0.42 μm、0.17 μm、0.15 μm，相对误差分别为2.3%、0.5%、1.1%。     

基于4f的大视角剪切散斑干涉系统设计

数字剪切散斑干涉技术在工业无损检测领域有广阔的应用前景,传统的迈克尔逊型数字剪切散斑干涉仪由于结构的限制,视场角很小,这限制了其在工程上的应用。介绍一种新型的大视角剪切散斑干涉系统,通过在成像镜头和CCD传感器之间嵌入4f光学系统来扩大其视场角,并实现镜头的外置。理论分析证明,视场角不再受到迈克尔逊结构的限制,仅仅取决于镜头的焦距和CCD传感器的靶面尺寸。设计并组建了一个大视场角迈克尔逊剪切散斑干涉系统,对比实验表明,在短的工作距离下实现了大视场的全场检测,在1 m的测距下,新系统测量面积可达800 mm600 mm,而传统的系统测量面积只有250 mm200 mm。     

融合散斑干涉技术的阵列式洛伦兹力微颗粒探测方法

提出了一种阵列式洛伦兹力微颗粒探测法,该方法结合了散斑干涉技术的全场位移测量、分辨率高等特性与洛伦兹力微颗粒探测法中探测量为矢量、可探测内部缺陷等优势,探索了一种实时、在线、原位的缺陷检测方法.针对阵列式洛伦兹力微颗粒探测法中阵列式排布的多个悬臂梁位移测量问题,设计了大剪切数字散斑干涉系统,使来自于被测悬臂梁和安装悬臂梁的横梁的反射光发生干涉,形成剪切干涉,通过对相位差进行分析获得悬臂梁的绝对位移,并且以洛伦兹力及悬臂梁末端的位移量为中间量建立了散斑干涉相位差与缺陷体积之间的关系.本文通过实验成功获得了悬臂梁全场位移量以及缺陷的体积,通过散斑干涉的方法测量悬臂梁位移量理论分辨率可达30 nm,这使洛伦兹力微颗粒探测法具备了微米级缺陷的探测能力.     

应用ESPI研究强激光作用下金属材料的热变形

本文讨论用电子散斑干涉技术（ＥＳＰＩ）测量激光引起的热变形的方法。给出两种实验装置，分别用来测量面内变形和离面变形，讨论了测量原理，给出测量结果。     

用于声-地震耦合探雷的激光测振技术研究进展（英文）

基于地雷独特机械特性和声-地震耦合原理的声-地震耦合探雷技术,在埋设地雷的安全有效探测方面具有广阔的应用前景,但针对实用工程探雷系统的研究还需要做大量工作。其中,声波耦合的地表振动信号非常微弱复杂,如何对其进行精确快速测量是一个关键难题。本文在声-地震耦合探雷技术原理的基础上,对地表振动的非接触激光测量技术(包括激光多普勒干涉技术、电子散斑干涉技术和激光自混合干涉技术)进行综述分析,并分析了电子剪切散斑干涉技术用于声-地震耦合探雷的可行性。     

一种可移动超分辨成像系统的制备及其性质研究

基于浸没透镜设计了一种超分辨成像系统,利用SU-8光刻胶和直径为4.87 m的微球实现纳米级别的超分辨成像。介绍微球成像放大率的求解方法,并通过软件模拟了超分辨成像系统的焦距。通过改变SU-8胶的厚度（从3.4 m到0）,系统的放大率也随之改变（放大率从1.6x到2.6x）。实验表明:SU-8胶的厚度对微球放大率有直接影响,通过该系统可以在普通光学显微镜下观察到蓝光光碟条纹。     

Strain measurement of SU-8 photoresist by a digital image correlation method with a hybrid genetic algorithm

Digital image correlation (DIC) is a whole-field and non-contact strain measuring method. It could provide deformation information of a specimen by processing two digital images that are captured before and after the deformation. To search the deformed images, a hybrid genetic algorithm, in which a simulated annealing mutation process and adaptive mechanisms are added to the real-parameter genetic algorithm, is proposed in this work. To increase the accuracy and reliability of this method, some key parameters of this method are suggested. Then, this method is used to measure the strain during the micro tensile testing of SU-8 photoresist. In addition to the conventional single region, a double region is proposed to calculate the strain by DIC. The results indicate that while the strains obtained by single region are reasonable, those obtained by double region are accurate. Also the mechanical properties of SU-8 could be accurately obtained.     

严格电磁场波导方法的三维厚胶光刻工艺仿真（英文）北大核心CSCD

无论是在微机电系统(MEMS)还是集成电路(IC)领域,SU-8厚胶光刻已经成为制造高深宽比结构的主流工艺。为了取代昂贵而耗时的光刻实验,一套能够良好预测显影形貌,从而为优化光刻制造提供有效帮助的光刻仿真软件就成为必要而有价值的工具。基于严格电磁场波导法的理论,给出一种针对SU-8光刻胶在紫外光下的三维光刻仿真模型。利用该模型,能很好地预测显影后的光刻胶内光强分布和立体形貌。并完成了一系列仿真和实验结果来验证模型的有效性。仿真结果给出横截面光强分布图和显影立体形貌模拟图形,并与相应的实验结果进行对照。结果验证了本文提出的仿真模型的正确性,并且表明三维混合模型在保证精确性的前提下,较之其他仿真算法运算速度更快。     

Measurement of residual stress by phase shift shearography

This paper presents a method for evaluating residual stresses. The approach is based on measuring the deformation due to the relief of stress produced by a drilled-hole or a ball indentation, and the deformation is rapidly measured by digital shearography. This method does not require mounting strain gages/transducers. Unlike holography, shearography does not require special vibration isolation. These features make the method practical for evaluation of residual stresses in a production/field environment.     

Photothermally enabled lithography for refractive-index modulation in SU-8 photoresist

We present a new lithographic technique based on a hybrid photothermal process to modulate the refractive index in commercial SU-8 photoresist. Owing to a difference in cross-linking, the refractive index of unexposed SU-8 cross-linked by thermally induced polymerization is 0.0072 higher than that of SU-8 cross-linked by UV exposure and postbaking. Making use of this property, we fabricated two thick, flat-topped index-modulated diffractive optical elements (DOEs) that contain different phase distributions and measured their wavefront reconstruction. The good experimental reconstructions of the index DOEs demonstrate the potential to extend the refractive-index modulation technique for the fabrication of three-dimensional optical elements without needing a development step.     

New concept of failure of thin organic films

A critical (steady state) value of the thermal expansion coefficients of different coatings was determined by a nondestructive technique (NDT) known as laser shearography. The behavior of organic coatings, i.e., ACE premium-grey enamel, a yellow acrylic lacquer, and a gold nail polish on a metallic alloy, i.e., a carbon steel, was investigated over a temperature range of 20–60 °C. The value of the thermal expansion coefficients of coatings was derived from the slope of the plot of the thermal deformation (strain) versus the applied temperature. The integrity of the coatings with respect to time was assessed by comparison the measured coefficients of thermal expansion (CTE) to the critical (steady state) or asymptotic value of CTE. By shearography, measurement of coating properties could be performed independent of parameters such as UV exposure, humidity, presence of chemical species, and other parameters which may normally interfere with conventional methods of the assessing of the integrity of coatings. Therefore, one may measure CTE of coatings, regardless of the history of the coating, in order to assess the integrity of coatings. Also, the obtained shearography data were found to be in a reasonable trend with the data of electrochemical impedance spectroscopy (EIS) in 3%NaCl solution.     

Direct removal of SU-8 using focused laser writing

SU-8 photoresist is an important material used in the development of micro-devices [1]. Cross-linked SU-8 structures have been known for their thermal stability and their strong resistance to standard solvent, acid and base. Due to the inert properties of this polymer, it is difficult to further modify or remove SU-8 once it is completely cured. We report an effective process to pattern cured SU-8 photoresist on glass using focused laser beam. Laser fabrication has been an important tool in various fields of research [2]. We made use of this laser cutting method to create interesting and useful two-dimensional SU-8 structures. The shapes and sizes of the structures created can be controlled by varying the power of the laser, angle of incident of the focused laser beam, the relative speed with which the laser beam traverse through the SU-8 film and the magnification of objective lens used. Besides two-dimensional structures, we can also create three-dimensional structures. In this case, we made use of a combination of controlled depth cutting and undercutting where focused laser beam is transmitted through the transparent substrate. Some possible applications of the laser patterned SU-8 film are also demonstrated in this work. PACS 42.62-b; 42.82.Cr; 79.60.Fr; 79.20.Ds; 78.66.-w     

厚度误差对THz-TDS的测量不确定度分析

阐述了基于菲涅尔公式的透射式太赫兹时域光谱系统提取样品光学常数的方法和原理,分析了样品厚度误差对THz-TDS测量不确定度的影响,并建立了相应的不确定度模型。进行太赫兹时域光谱测量实验,提取硅片在太赫兹波段的折射率,并计算了误差对提取样品折射率的影响。结果表明,随着厚度误差的增大,系统测量偏差也随之增大。对于较厚样品,相同厚度误差对其测量结果影响较小。样品厚度为994μm时,在厚度存在1μm的测量误差情况下,系统测量折射率的偏差为0.001 2,接近模型的仿真值。实验结果验证了厚度误差对测量不确定度模型的有效性,了解了厚度误差对系统测量结果的影响情况,对测量过程及结果分析具有一定的指导意义。     

Large-format fabrication by two-photon polymerization in SU-8

Microporous structures are central to many fields of science and engineering, but many of these systems are complex with little or no symmetry and are difficult to fabricate. We applied two-photon polymerization (2PP) and femtosecond laser direct-writing techniques to fabricate broad-area large-format 3D microporous structures (450 μm × 450 μm × 40 μm) in the epoxy-based photoresist SU-8. The appropriate exposure was determined by controlling average pulse energies and stage speeds to generate the exposure curves. Mechanical distortion exhibited in suspended walls fabricated by 2PP laser writing was studied by controlling wall lengths and widths. A simple thermal-expansion model is presented to explain the distortion caused by axial loadings of the walls.     

考虑底充胶固化过程的InSb面阵探测器结构分析模型

液氮冲击中In Sb面阵探测器的易碎裂特性制约着探测器的成品率,建立适用于面阵探测器全工艺流程的结构模型是分析、优化探测器结构的有效手段.本文提出了用底充胶体积收缩率来描述底充胶在恒温固化中的体积收缩现象,同时忽略固化中底充胶弹性模量的变化来建立底充胶固化模型,给出了底充胶在恒温固化中生成的热应力/应变上限值.借鉴前期提出的等效建模思路,结合底充胶固化后的自然冷却过程和随后的液氮冲击实验,建立了适用于In Sb面阵探测器全工艺流程的结构分析模型.探测器历经底充胶固化、自然冷却至室温后的模拟结果与室温下拍摄的探测器形变分布照片高度符合.随后模拟液氮冲击实验,得到面阵探测器中累积的热应力/应变随温度的演变规律,热应力/应变值极值出现的温度区间与液氮冲击实验结果相符合.这表明所建模型适用于预测不同工艺阶段中面阵探测器的形变分布及演变规律.