Nanoscale deformation measurement by using the hybrid method of gray-level and holographic interferometry

This study extends the use of holographic interferometry to measure the nanoscale out-of-plane displacement with high surface resolution. It is noted that if the deformation is less than half of the optical wavelength, it is hard to find an obvious fringe pattern. Under such a situation, in general, the phase shift method is used. However, it needs to take more than 3 images for phase shifting and phase reconstruction In this paper, a more simple hybrid method of gray-level and holographic interferometry is used to extract fringe skeletons, in which it just needs to take one or two images for the normal deformation measurement directly, even if there exists no obvious fringe pattern. The displacement field with high surface resolution can also be obtained. The proposed method yielded a theoretical precision of 0.15 nm for out-of-plane displacement with a monochromatic CCD camera of 10-bit gray scale (1024 gray scales) sensitivity and microscale surface resolution for millimeter scale object with 640×480 pixels image resolution by an He–Ne LASER (632.8 nm wavelength) light source. The gray-level method is proposed to calculate the non-obvious interferometry fringe by traditional holographic interferometry hologram, and the result showed that this method works for this purpose.     

高频位相型曲面变形光栅的转移工艺研究

本文研究了在室温和８５℃温度环境下高频位相型曲面变形光栅的转移工艺。实验结果表明：通过这种方法可以复制出高质量的曲表面试件变形栅，并具有灵敏度高、条纹质量好、方法简便、可用于工业现场等优点。为云纹干涉法对曲面变形问题的研究提供了重要的手段。     

Instantaneous velocity measurement of dynamic deformation by digital holographic interferometry

A novel method for the instantaneous velocity measurement of dynamic deformation by digital holographic interferometry is proposed. During dynamic deformation, a series of digital holograms is recorded by a high-speed camera. At each pixel of the phase difference maps, phase and amplitude information are combined as complex phasor (CP). Each pixel can be then considered as an independent sensor and a sequence of complex phasors of such a sensor is analyzed by short time Fourier transform (STFT) along the time axis. A fast iterative algorithm is developed for the computation of instantaneous velocity. The displacement of each pixel can also be obtained by integration of the instantaneous velocity over time and phase unwrapping process is thus avoided. The performance of the proposed CP method is compared experimentally with the commonly used digital phase subtraction method.     

用激光测量高热可靠性电子器件的热变形

本文提出了一种测量大功率电子器件热变形的双曙光激光全息干涉法，针对一种可靠性要求很高的电子器件-火箭点火用固态继电器进行实际测试，试验结果表明，固态继电器在大负载功率工作状态时，芯片表面的干涉条纹较多，条纹弯曲程度较大，因此反映了芯片热变形和热应力增大趋势较为明显。     

Comparative accuracy of holographic interferometry and speckle photography for out-of-plane deformation measurement

Out-of-plane deformation of a surface can be measured either by recording a double exposure hologram, or by taking a double exposure speckle photograph with the camera deliberately de-focused. In the latter case the local surface tilt is measured, and the profile change subsequently obtained by integration. It is shown that errors can arise in speckle photography due to focusing the camera incorrectly, whereas the holographic method is not affected instrumentally. The sensitivity of the speckle method can approach that of holographic interferometry, but without requiring the same interferometric stability of recording apparatus.     

形貌与微变形全场光学同时测量方法

在实际工程应用中,对材料形貌和结构变形等参量的检测是必不可少的,而且往往需要进行多参量同时测量。针对该背景,采用数字散斑干涉与数字条纹投影相结合的测量方法, 设计了一种集成光路,通过在数字散斑干涉实验光路中引入一个投影设备,实现物体表面形貌和微变形的同时测量。所提出的方法具有全场非接触测量的优点,且测量光路简单、操作方便、效率高、可靠性强。该方法的形貌测量分辨率优于10 μm,形变测量分辨率优于30 nm。     

Picosecond three-color holographic digital interferometry

The possibilities of multicolor digital holographic interferometry are experimentally studied upon measuring displacements of a surface in radiation of a picosecond Nd:YAG laser with the radiation frequency conversion into harmonics (λ₁ = 1.06 μm, λ₂ = 0.53 μm, and λ₃ = 0.35 μm). It is shown that three-color digital holographic interferometry makes it possible to increase the measurement accuracy of displacements. The peculiarities of multicolor digital holographic interferometry by picosecond pulses are discussed.     

Pulsed digital holographic interferometry by using a flexible fiber endoscope

A system based on digital holographic interferometry in combination with a flexible fiber endoscope is described. A Q-switched pulsed laser is used. Two digital holograms of the test object, corresponding to the two laser pulses, are captured at separate video frames of a CCD-camera, transferred in a frame grabber and further processed in a PC. If the object undergoes a deformation during the interval between the two laser pulses (usually in the range of 5–600 μs), a fringe pattern will result from the difference between the two holograms. This fringe pattern has the information needed to evaluate quantitatively the amount of the deformation. A compact system has been developed to be used for various applications, both mechanical and biological, where measurements need to be performed at “hidden” surfaces or inside more or less closed objects. The quality of the results obtained by using mechanical objects is usually better than for biological objects. This can be explained easily by the fact that a biological surface is much more complex, in particular some parts of the surface may reflect the light well whereas some other parts may absorb it. Experimental results are presented.     

Analogue difference holographic interferometry for two-wavelength contouring

Difference holographic interferometry uses holographic illuminations from the master object for the illuminations of the test object. The principle has been applied successfully for deformation measurement, phase object investigation and for contouring, as well - but in the last case within the two-refractive index method, only. Its application for contouring with the two-wavelength method is still missing - although it does exist already in the much later developed digital holographic interferometry.The present paper resolves this discrepancy and provides the better “analogue quality” by reporting the first realization of the analogue difference holographic interferometry in the two-wavelength contouring. Experimental evidence is presented not only for the existence of the application but for the numerical correctness of difference making, too. The measuring range extension achieved is threefold.     

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。