基于白光干涉的空间频域算法研究

为了精确定位白光干涉条纹的零光程差位置,采用空间频域算法通过傅里叶变换提取白光干涉信号中心波长的相位信息并结合包络中心算法去除相位模糊从而实现零光程定位.实例测量了具有相位突变的计算全息元件的表面轮廓,其平均刻蚀深度为1.63 μm.测量表面形貌连续分布的微透镜阵列,0.32 mm×0.32 mm视场内表面PV为370...     

低相干光干涉法延时测量中的误差分析

低相干光干涉法通过测量宽谱光通过待测器件之后的相位变化得到其相对延时量。采集宽谱光时域干涉数据,利用傅里叶变换提取出频域相位信息后再进行相位展开、多项式拟合处理,所得相位曲线对频率求导可得待测延时曲线。延时测量误差来源于干涉信号强度误差和纯相位误差。理论分析和仿真计算表明,延时误差与相位误差成正比;强度噪声引起的相位误差与噪声强度成正比,且该类噪声可通过曲线拟合算法得到有效抑制。实验表明,温度等环境因素引起的纯相位误差是延时测量误差的主要因素。实验上,对约19 m光子晶体光纤于1540~1560 nm波段的相对延时进行了测量,达到了0.14 ps的精度。     

偏振耦合测试及其振动干扰信号分析

理论分析了偏振模式耦合的原理,给出了基于白光干涉的偏振耦合检测方法。通过步进电机控制迈克耳孙干涉仪扫描臂的反射镜移动,改变干涉仪两臂之间的光程差(OPD),补偿了由于偏振耦合而形成的两偏振光从保偏光纤(PMF)出射时的光程差,实现了对保偏光纤的偏振耦合强度和位置的测试。扫描过程中扫描臂反射镜的振动会对输出信号产生不良影响,对此振动信号进行了仿真及实验研究,分析了它对输出信号的影响。在不同的扫描速度下,采用Hilbert变换和最小二乘高斯非线性回归分析提取白光干涉包络,求解耦合强度,验证了振动信号的幅度和频率与扫描速度有关,以及它对耦合强度检测精度的影响。结果表明该测试系统动镜的扫描速度在0.7～0.9mm/s时,偏振耦合强度的检测误差最小。     

基于Curvelet变换的ESPI图像散斑噪声抑制算法研究

重点研究了Curvelet变换的去噪原理及方法,并结合ESPI条纹图中散斑乘性噪声的特性,提出了改进的Curvelet变换去噪方法,即在去噪之前,先将图像进行对数变换,使得乘性噪声变成加性噪声,然后再进行Curvelet变换去噪,这样会更有利于噪声与边缘信息的分离。并把该方法应用在对轮胎的激光无损检测图像处理系统中,实验结果表明该方法在有效去除散斑噪声的同时,较好地保持了条纹图的边缘细节信息。     

实时数字全息测量温度场研究

利用数字全息干涉术研究了气流温度场的分布,对实验中所采集的干涉条纹图像进行傅里叶变换,数字低通滤波和傅里叶逆变换处理以消除散斑噪声影响,确保了气流场干涉条纹相位信息的高对比度和低噪声,并对其进行提取和展开;根据理论研究的相位与折射率的关系求得气流场的温度分布,实验结果与热电测量的结果基本一致,表明了实时数字全息干涉术是一种测量温度场的有效方法,具有极好发展和应用前景。     

相移干涉术中参考波准直误差的数值校正

针对相移干涉术中参考波由于准直误差可能为非倾斜或倾斜球面波的情形,本文提出了一种简单的数字处理方法,不需任何附加测量即可提取真实球面波的几何参数,进而校正由标准波前再现公式所恢复的物波波前误差.本文方法的有效性由模拟试验所证实,并说明了其适用范围.     

Moiré Interferometry Assessement of Residual Stress Variation in Depth on a Shot Peened Surface

Abstract: The main goal of this work was the development of experimental techniques to measure in depth non‐uniform residual stresses, as alternative to the more conventional hole‐drilling method with strain gauges. The proposed experimental methodology is based on moiré interferometry. This high resolution field technique allows in‐plane displacement assessment without contact. Grating replication techniques were also developed to record high quality diffraction gratings onto the specimen’s surface. A laser interferometry setup was implemented to generate the master grating (virtual). The stress relaxation was promoted by blind hole‐drilling and the obtained fringe patterns were video recorded. Image processing techniques were applied to assess the in‐plane strain full‐field. A finite elements code (FEM), ANSYS^®, was used to simulate the stress relaxation process and to calculate the hole‐drilling calibration constants.     

Experimental and Numerical Investigation of Strain Distributions Within the Adhesive Layer in Bonded Joints

Abstract: We present the results of investigations into the strain distributions in the adhesive layers of epoxy‐bonded aluminium–aluminium and aluminium–carbon fibre reinforced polymer (Al/CFRP) double‐lap shear joints. The area of the adhesive at the end of the overlap region, where high stresses are predicted and failure generally initiates, has been studied at high magnification. 2‐D maps of the longitudinal and engineering shear strains in this region have been obtained experimentally by using high magnification moiré interferometry (HMMI). These results have been compared with the strain maps predicted by 3D elastic and elasto‐plastic finite element (FE) modelling. Excellent agreement is seen between the experimentally measured and FE‐predicted strain distributions, thus validating both methods. In some cases, quantitative comparison of the strains along certain profiles is compromised by noise in the measurements, especially for the Al/CFRP joints, which experienced lower overall strains. The source of such errors is discussed in the paper.     

氮气短间隙的耐受电压和气体密度恢复特性

为了提高气体火花开关重复运行频率,对氮气短间隙的耐受电压和气体恢复特性进行了研究。采用＂双脉冲法＂获得了气隙耐受电压恢复特性,利用Mach-Zahnder干涉仪记录了气体密度的恢复过程,用CCD相机拍摄了放电图像。实验发现：耐受电压恢复过程分为静态击穿电压恢复和过电压击穿能力恢复两个阶段,后者所需的时间远超过前者。即使气体密度完全恢复了,气隙也仅恢复其静态击穿电压,其原因可能是放电残留的长寿命氮原子在阴极上复合导致阴极电子发射,持续不断地为放电提供初始电子。＂双脉冲法＂实验中气隙两次击穿的路径通常是分离的,说明气体绝缘最薄弱之处并不一定位于第1次火花放电通道上。     

基于迭代梯度算法的子孔径拼接检测技术研究

为了解决粗大调整误差下大口径光学平面镜的子孔径拼接检测问题,基于迭代梯度算法,建立了一套合理的拼接算法和数学模型,同时编制了拼接程序。结合工程实例,利用Φ600mm干涉仪实现了对Φ800mm平面镜的拼接测量。检测中,基于靶标对各子孔径实现对准,拼接所得面形光滑连续无狭缝。实验结果表明,利用迭代梯度算法可以高精度地完成粗大调整误差下大口径平面镜的拼接检测。