空间载频干涉法全场测量长度技术

在研究二维快速傅里叶变换法进行干涉测试基本原理的基础上,提出一种基于二维快速傅里叶变换的长度测量法.以量块长度的测量为对象,被测量块置于泰曼-格林干涉仪测试光路中,参考光波分别与待测长度的量块表面和辅助平面反射的测试光波形成干涉条纹,条纹由图像采集系统采集.利用编制的算法处理软件,通过处理干涉条纹图中量块边缘识别、区域延拓、滤波、波面统一,获得了量块全场表面的空间长度分布,实现了对量块长度的自动化测量.结果表明:该测量法不仅具有较高的测量准确度,而且具有全场测试和非接触测量等优点.     

一种分析薄膜振动模式的结构光条纹时间平均法

提出了一种用于振动物体表面快速测量的光学测试系统和方法。该系统采用结构光三维传感技术,利用时间平均法来实现对振动表面的测量和振动模式分析。用低帧频商用CCD相机记录由光栅投影到振动物体表面上形成的一系列变形正弦条纹,对获取的一帧变形条纹经过二维傅里叶变换、频谱滤波、逆傅里叶变换等处理得到调制物体振幅的零级贝塞尔函数分布。给出了该方法的理论分析,推导了相应的计算公式。计算机模拟和实验验证了该方法的可行性。实验证明,该方法具有数据获取速度快,全场非接触测量以及实验装置简单等优点。     

基于快速傅里叶变换的条纹图像处理研究

为提高船体扭转角变形测量精度,对双光栅干涉测量法产生的莫尔条纹采用快速傅里叶变换频域处理。采集不同宽度的莫尔条纹图像,分别对图像进行快速傅里叶变换,对比分析图像频谱,得到实际莫尔条纹图像的有效频率信息。分析滤波器的选择原则,选用陷波低通滤波器,去除频域图像中高频噪声,获得莫尔条纹有效信息。实验结果表明,莫尔条纹的频域处理精度远高于空域处理结果,使扭转角测量精度提高到1.2″。     

干涉测量系统中杂散条纹影响的抑制

 为了抑制杂散条纹的影响，提出了一种简单实用的单幅三表面干涉条纹傅里叶分析法，它根据三表面干涉时各个表面干涉的条纹调制度不同，从三表面干涉图的频谱中提取测试面的频谱，从而准确地恢复测试面的面形。模拟结果证明了该方法的有效性，准确度可以达到l/1 000。实验表明：单幅三表面干涉条纹傅里叶分析法得到的面形形状与波长调谐时域傅里叶变化法和涂消光漆法得到的结果基本一致，PV值和RMS值与波长调谐时域傅里叶变化法相差分别为0.001l和0.004l，与涂消光漆法相差分别为0.042l和0.019l。通过7次单幅三表面干涉条纹傅里叶分析法测量，得到PV和RMS值的重复性分别为0.007 8l和0.002 6l。     

复杂脉冲单发频域干涉测量

以傅里叶变换极限脉冲作参考脉冲,利用单次测量分析法对复杂的皮秒脉冲进行测量,用窗口傅里叶变换代替傅里叶变换对干涉条纹进行时间-频率分析,直接提取出复杂脉冲的啁啾特性或光谱成分,将光谱图中的功率密度S(ω,t)沿ω轴求和重建脉冲的时域包络.分别用该方法和传统频域干涉测量法测量一个线性啁啾脉冲和一个复杂脉冲.结果表明,该方法可实现复杂整形脉冲的实时测量,且时间分辨率为70 fs.     

基于窗口傅里叶变换剪切干涉法波前检测

提出了一种利用二维窗口傅里叶变换从径向剪切干涉条纹中准确得到波前的重建技术。首先对剪切干涉条纹做二维窗口傅里叶变换,设置阈值和频率积分范围后,进行二维窗口傅里叶逆变换,然后对包裹相位做去载频和相位展开处理得到相位差分布,最后使用波前迭代算法从相位差中复原实际波前。模拟计算表明,使用该方法最大相位复原误差为0.82%,均方根值为0.020 9 rad,实验结果验证了该方法的有效性。同时也对窗口傅里叶变换的关键参数,如窗函数的选择、窗口大小的确定以及阈值的选取等进行了简要讨论。与传统傅里叶变换法(FFT)相比,基于窗口傅里叶变换的剪切干涉波前检测法有更高的精度和稳定性,为波前检测提供一种新的处理方法。     

基于迈克尔逊干涉的傅里叶变换散斑形貌测量技术

提出了电子散斑干涉载频调制测量物体形貌的方法。采用典型的迈克尔逊干涉光路,将物体偏转一微小角度（等效为物面与参考面间形成空气楔）产生等厚干涉,可在物体的表面引入包含物体高度信息的载波干涉条纹。用CCD采集该载波条纹图,利用傅里叶变换法可解调出物体高度的位相信息,从而实现物体的形貌测量。介绍了电子散斑干涉载频调制测量物体形貌的原理,并进行了实物测量,给出了实验结果。由于该方法采用散斑干涉方法测量物体形貌,所以具有灵敏度高的优点。     

长度测量中干涉条纹的自动识别技术研究

利用激光干涉与数字图像处理技术以及应用FFT分析干涉条纹方法,分析并解决了测量端面长度标准中条纹图的处理技术,应用这种方法不但提高了测试过程的自动化程度,而且大大地提高了测量结果的精度,并给出了最典型的端面长度标准量块的干涉条纹小数部分的实测结果.     

一种基于傅里叶变换的分析载波条纹的新方法

针对传统傅里叶变换法处理光载波干涉条纹图时会有边缘效应产生的问题,提出了一种基于傅里叶变换法的外推延拓方法,并从理论上进行了数学推导。为了验证这种方法的正确性,分别对一维数字信号和二维空间载波条纹图进行了数值模拟,进一步分析了误差产生的原因,并与传统的傅里叶变换法对比。结果表明该法可以有效抑制传统傅里叶变换法处理光载波干涉条纹图时边缘效应所造成的较大误差,在基于空间域相位调制技术的波面干涉测量中,对空间载波条纹图进行处理,可以使相位的计算精度达到3.3 mrad。     

干涉条纹快速加窗傅里叶滤波方法的研究

滤波是干涉图像处理中的关键问题之一。为解决加窗傅里叶滤波在干涉条纹处理中运行时间长的问题,采用了快速傅里叶变换算法用以减少计算时间。通过加窗傅里叶变换,克服了傅里叶变换在干涉图相位局部信息不能提取的缺点,提出了一种快速加窗傅里叶滤波方法,实现了干涉条纹的快速滤波。在保证滤波效果的同时,缩短了计算时间,大大提高了干涉条纹处理速度,从根本上解决了加窗傅里叶滤波耗时长的问题,使得加窗傅里叶滤波方法应用于散斑在线检测成为了可能。实验验证了本方法的快速性、有效性和可靠性。     

应用移相干涉术测量量块长度和长度变动量

研究了应用移相干涉术测量新的一等量块的方法。对于干涉图像进行多幅图的采样，由移相法计算量块测量面和与其研全的辅助平晶表面的波面面形，着重研究了在量块干涉图中有阶跃不连续的波面复原运算的原理与技术，得到一幅表征它们表面的离散滤差值，并给出量块工作面长度和长度变动量的测量结果。     

Height gauge based on dual polarization competition laser

Based on dual polarization competition laser, we develop a new height gauge. By inserting a quartz crystal plate into the laser cavity, one laser beam splits into two orthogonally linear polarized laser beams, which appear one after another with the change in cavity length. After detecting their intensities, we obtain two power-turning curves. The longitudinal mode spacing is divided into 4 equal zones and each one has different intensity phenomena, which provides a new method of height measurement. According to experiments, the direct measuring range of this new method is 12 mm with resolution of 79.1 nm, and the indirect measuring range can be increased using first grade gauge blocks and a liftable platform. Compared to other height gauges such as vernier gauge, inductance sensor and gauge block interferometer, this new instrument has the advantage of self-calibration and simple structure without frequency stabilization system.     

A new method of noncontact gauge block calibration using the fringe counting technique: II. Experimental verification

An experimental verification of a new noncontact interference method for gauge block or length bar calibration is presented. In this technique, the length of the tested artifact is measured by means of the counting fringe method. A new technique for central interference fringe detection is used for evaluation of the end surface positions of the measured artifact. The experimental set-up and length measurement procedure are described. Preliminary experimental results and uncertainty analysis of the proposed method are presented.     

Quantum Gravitational Contributions to Gauge Field Theories

We revisit quantum gravitational contributions to quantum gauge field theories in the gauge condition independent Vilkovisky-DeWitt formalism based on the background field method.With the advantage of Landau-DeWitt gauge,we explicitly obtain the gauge condition independent result for the quadratically divergent gravitational corrections to gauge couplings.By employing,in a general way,a scheme-independent regularization method that can preserve both gauge invariance and original divergent behavior of integrals,we show that the resulting gauge coupling is power-law running and asymptotically free.The regularization scheme dependence is clarified by comparing with results obtained by other methods.The loop regularization scheme is found to be applicable for a consistent calculation.     

Optimizing X‐ray mirror thermal performance using matched profile cooling

To cover a large photon energy range, the length of an X‐ray mirror is often longer than the beam footprint length for much of the applicable energy range. To limit thermal deformation of such a water‐cooled X‐ray mirror, a technique using side cooling with a cooled length shorter than the beam footprint length is proposed. This cooling length can be optimized by using finite‐element analysis. For the Kirkpatrick–Baez (KB) mirrors at LCLS‐II, the thermal deformation can be reduced by a factor of up to 30, compared with full‐length cooling. Furthermore, a second, alternative technique, based on a similar principle is presented: using a long, single‐length cooling block on each side of the mirror and adding electric heaters between the cooling blocks and the mirror substrate. The electric heaters consist of a number of cells, located along the mirror length. The total effective length of the electric heater can then be adjusted by choosing which cells to energize, using electric power supplies. The residual height error can be minimized to 0.02 nm RMS by using optimal heater parameters (length and power density). Compared with a case without heaters, this residual height error is reduced by a factor of up to 45. The residual height error in the LCLS‐II KB mirrors, due to free‐electron laser beam heat load, can be reduced by a factor of ～11 below the requirement. The proposed techniques are also effective in reducing thermal slope errors and are, therefore, applicable to white beam mirrors in synchrotron radiation beamlines.     

基于光弹性贴片法的材料表面应变场测量研究

针对常用电阻应变片法的点测结果不易反映构件表面应变场分布的问题,将光弹性贴片方法应用于材料表面应变场测量。制作了光弹性贴片,并标定光弹性贴片的材料条纹值,通过几种典型形状光弹性贴片试件的加载实验掌握应力场分布的条纹图像判读方法。开展光弹性贴片在简支钢梁的应变场测量应用,在薄弱点位置光弹性贴片法相比电阻应变片法应变值偏差在5%以内。对C30混凝土试块进行4.4 MPa～39.6 MPa的应力加载过程中,有效监测到混凝土表面裂缝产生、稳定扩展及失稳破坏过程中的条纹图像变化过程。实验表明,光弹性贴片方法可以直观可靠地测量金属及混凝土的表面应力场变化。     

CANONICAL QUANTIZATION OF GAUGE FIELDS (Ⅲ)——GRAVITATIONAL FIELD

The gravitational field is quantized within the canonical formalism under theharmonic gauge condition.The gravitational field is decomposed into transversalfields and self-commuting fields.The equation of motion of the self-commuting field X_μ is derived,and the contributions of self-commuting fields to physical S-matrixelements are investigated.Then the gauge compensating term of the effective actionis obtained.The result is in agreement with that obtained by the path integral method,but with our method the difficulty of the Gribov gauge ambiguity can be overcome.     

各向异性焊缝中超声相控阵瞬态声场仿真及缺陷定位方法

针对多层各向异性奥氏体不锈钢焊缝中超声相控阵瞬态声场的仿真问题,提出应用高斯声束等效点源模型计算宽带离散化的多个单频稳态声场,通过傅里叶变换将其拓展为瞬态声场,并分析了声场转换过程的主要影响参数。该方法可快速计算焊缝内部超声相控阵聚焦声场的瞬态能量分布和任意一点的时域波形信号。在此基础上针对多层奥氏体不锈钢焊缝内部缺陷的超声相控阵成像检测问题,提出利用上述时域高斯声束法对多通道缺陷散射信号进行时间反转计算,并根据时域声场焦点确定缺陷位置。最后通过实验,验证使用此方法检测实际奥氏体不锈钢焊缝试块内部缺陷的效果。结果表明,提出的方法能够确定缺陷位置,且计算速度快、运算量小,适合作为多层介质内部缺陷实时成像的声场仿真模型。      

Thermal lens determination of LD end-pumped solid-state laser with stable resonator by slit scanning method

A simple method to determine the thermal focal length of LD end-pumped solid-state laser with stable resonator is presented. The M² factor describing the quality of the beam can be obtained by scanning a slit through the multi-mode Gaussian beam field. The waist width of the beam and the corresponding TEM₀₀ under the same parameters of laser are then deduced through the law of multi-mode Gaussian beam propagation. Based on the standard matrix theory of stable resonator, the thermal focal length of the gain medium can be easily achieved. To show the application of this approach, the thermal focal length of an LD pumped Nd:YVO₄ laser is measured and the experimental results are in agreement with the theoretical prediction.     

Simultaneous measurement of whole in-plane displacement using phase-shifting ESPI

A novel method for simultaneously measuring whole field in-plane displacements by using optical fiber phase-shifting electronic speckle pattern interferometry (ESPI) is presented in this paper. A 1 × 4 single mode optical fiber beamsplitter is employed to split the laser beam into four beams of equal intensity. One pair of fibers is utilized to illuminate the diffuse target at equal angles in the horizontal plane so it is sensitive only to horizontal in-plane displacement. Another pair of optical fibers is set to be sensitive only to vertical in-plane displacement. The polarization directions of light emitted by fibers are the same for each pair, but are at a right angle between pairs. The optical fibers are equal in length for each pair, but are not equal between two pairs. In this case the speckles are interference between each pair of fibers, thus the horizontal and vertical displacement components can be obtained simultaneously. By means of a fiber phase shift technique we can obtain the quantitative data of whole field displacements. This method has made it possible to study the in-plane displacement of a thin metal plate, and the examples of the results are shown to demonstrate the novel method.