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1.
An optical technique for slope detection by using as storing medium a photorefractive BSO crystal is proposed. The technique relays in that a local tilt produced in a diffusing reflective surface can be mapped as a speckle transversal shifting in a plane perpendicular to the optical axis. The volume nature of the storing medium is quite adequate to highlight the speckle volume nature and its associated properties. Experimental results obtained by using a rubber vibrating membrane are presented. 相似文献
2.
Electronic speckle interferometry (ESPI) is used to determine the Young's modulus E and Poisson ratio ν of an isotropic material. Micron scale deformations of the surface of the block of polymethyl-methacrylate (PMMA) are induced by normal application of a known near-point force. These deformations are recorded in speckle interferometric fringe patterns. An iterative minimum error inversion technique is developed to obtain the elastic properties from the positions of fringe peaks and troughs observed in the fringe patterns. Sensitivity tests of the method on calculated fringe patterns using measured experimental uncertainties suggest the technique will provide measures of the elastic moduli to better than 5%. In an experimental test on a bloc of PMMA (acrylic) the technique gave values of E and ν that differed from corresponding measures obtained using more conventional strain-gauge methods by less than 4%. 相似文献
3.
Spatial correlation properties are studied for speckle patterns produced in the diffraction region behind a lens which is located at a focal distance from a diffuser with an aperture under illumination of the coherent plane-wave light. It is shown theoretically that, if a ring-slit aperture of a negligible slit width is used, the speckle field produced has a perfect correlation in the longitudinal direction. An experiment was performed using a circular aperture and ring-slit apertures having different ratios of the inner to the outer radius and the speckle pattern produced using the ring-slit aperture with the smallest slit width had the longest longitudinal correlation in all cases examined. The statistical stationarity and symmetry of the speckle field, as well as variation in the speckle size, are also discussed. 相似文献
4.
弱散射屏产生的远场散斑由一个中央亮斑和一个分布于亮斑周围而与正态散斑类似的散斑结构, 根据弱散射屏远场的散斑图样, 人们假设弱散射屏产生的像面散斑为均匀背景与正态散斑两者相干叠加的结果, 但这种假设与实际像面散斑存在歧异, 基于上述情况, 本文利用4f高通滤波光学成像系统, 研究了高斯型弱散射屏产生的像面散斑场的统计特性, 得出只有表面均方根粗糙度与入射光波的波长相差不多时上述假设才是可行的结论.
关键词:
弱散射屏
f光学成像系统')" href="#">4f光学成像系统
像面散斑 相似文献
5.
A video-based laser speckle technique has been developed for noncontact analysis of fatigue in situ and at speeds approaching video frame rates. This technique, computed speckle decorrelation (CSD), makes use of the speckle decorrelation associated with surface deformation. It is a method of full field inspection which both locates fatigue damage sites and measures damage severity. In its current application, CSD has been used to study the fatigue deformation progression in reverse bending fatigue of a cylindrically notched aluminum specimen. However, film based studies have shown the usefulness of laser speckle decorrelation to analyze fatigue deformation of thick graphite/epoxy composite materials as well. With the development of the CSD method it will now be possible to examine in greater detail the progression of fatigue damage in these materials, allowing a much faster and more quantitative analysis than was previously available. 相似文献
6.
Luxi Li Paweł Kwaśniewski Davide Orsi Lutz Wiegart Luigi Cristofolini Chiara Caronna Andrei Fluerasu 《Journal of synchrotron radiation》2014,21(6):1288-1295
A new approach is proposed for measuring structural dynamics in materials from multi‐speckle scattering patterns obtained with partially coherent X‐rays. Coherent X‐ray scattering is already widely used at high‐brightness synchrotron lightsources to measure dynamics using X‐ray photon correlation spectroscopy, but in many situations this experimental approach based on recording long series of images (i.e. movies) is either not adequate or not practical. Following the development of visible‐light speckle visibility spectroscopy, the dynamic information is obtained instead by analyzing the photon statistics and calculating the speckle contrast in single scattering patterns. This quantity, also referred to as the speckle visibility, is determined by the properties of the partially coherent beam and other experimental parameters, as well as the internal motions in the sample (dynamics). As a case study, Brownian dynamics in a low‐density colloidal suspension is measured and an excellent agreement is found between correlation functions measured by X‐ray photon correlation spectroscopy and the decay in speckle visibility with integration time obtained from the analysis presented here. 相似文献
7.
A novel QNDT (quantitative non-destructive testing) method is developed that is combined with a phase-shifting shearing speckle and thermograph, and, it aims at the detection of faults such as cracks, voids, delamination and weak areas. The technique is immune to ambient noise and is suitable for measuring the in situ environment. Some different depth defects that would produce deformation differing from other positions could be found with shearing speckle when the sample is loaded, however, a thermograph based on the thermal resistance effect of a defect can detect only those varisized defects embedded deeply in the composite structure by measuring the surface temperature distribution. The resolution is examined for artificial delaminated defects in carbon-fiber composite structures using a phase-shifting shearing speckle and thermograph. The experimental results have demonstrated that the technique is effective for revealing defects in composite structures. 相似文献
8.
Junji Ohtsubo 《Optics Communications》1980,34(2):147-152
The vector velocity measurement of the in-plane object motion based on the dynamic properties of speckle patterns is conducted. The time-space cross-correlation function of speckle intensity variations is used to determine the magnitude and direction of the in-plane object velocity. Theoretical and experimental studies of the speckle correlation technique for the determination of the in-plane object velocity are discussed and the vector velocities of the diffuse object are displayed as a two-dimensional image. 相似文献
9.
双散斑场相移数字干涉计量 总被引:2,自引:1,他引:1
本文介绍了一种检测散射表面变形的自动测量系统。将相移和数字图像处理技术应用于数字散斑干涉计量中,毋须中间记录过程,在计算机控制下采集数据和计算相位,产生相位条纹而非相关条纹。用图像处理技术消除散斑随机性引起的噪声。文中给出了面内、离面变形的测量结果。 相似文献
10.
We present an effective method for speckle noise removal in digital speckle pattern interferometry, which is based on a wave-atom thresholding technique. Wave atoms are a variant of 2D wavelet packets with a parabolic scaling relation and improve the sparse representation of fringe patterns when compared with traditional expansions. The performance of the denoising method is analyzed by using computer-simulated fringes, and the results are compared with those produced by wavelet and curvelet thresholding techniques. An application of the proposed method to reduce speckle noise in experimental data is also presented. 相似文献
11.
The statistical properties of speckle intensity variations produced by coherent light in the diffraction field of diffusely transmitting objects are investigated experimentally with intimate relation to their surface roughness. The probability distribution and the average contrast of intensity variations in speckle patterns are studied as a function of the surface roughness of the objects and the receiving plane in the diffraction field. 相似文献
12.
The surface roughness properties (i.e. the rms surface roughness and the correlation length) of strong diffuse objects are investigated by using the speckle patterns which obeys the non-gaussian statistics. The intimate linear relation is found to exist between the rms surface roughness of objects and the maximum contrast obtained from the varying curves of the average image speckle contrast as a function of the point spread of an optical imaging system. The correlation length of surface roughness of objects is related to the averaged intensity distribution of speckle patterns produced at the far-field diffraction plane. It now becomes clear that the rms roughness and the correlation length of strong diffuse objects are determined, respectively, from the maximum speckle contrast at the image plane and the averaged speckle intensity distribution at the far-field diffraction plane. 相似文献
13.
Ningyu Zhang Chuanfu Cheng Shuyun Teng Xiaoyi Chen Zhizhan Xu 《Optics & Laser Technology》2007,39(6):1150-1154
A new approach based on the gated integration technique is proposed for the accurate measurement of the autocorrelation function of speckle intensities scattered from a random phase screen. The Boxcar used for this technique in the acquisition of the speckle intensity data integrates the photoelectric signal during its sampling gate open, and it repeats the sampling by a preset number, m. The average analog of the m samplings output by the Boxcar enhances the signal-to-noise ratio by , because the repeated sampling and the average make the useful speckle signals stable, while the randomly varied photoelectric noise is suppressed by . In the experiment, we use an analog-to-digital converter module to synchronize all the actions such as the stepped movement of the phase screen, the repeated sampling, the readout of the averaged output of the Boxcar, etc. The experimental results show that speckle signals are better recovered from contaminated signals, and the autocorrelation function with the secondary maximum is obtained, indicating that the accuracy of the measurement of the autocorrelation function is greatly improved by the gated integration technique. 相似文献
14.
This paper presents a feasibility study to assess whether digital speckle pattern interferometry could be used as a possible technique to investigate the adhesive performance of coatings. The approach is based on the measurement of the deflections produced by a pre-notched coated specimen subjected to a four-point bending test. When the bending load is increased, a delamination between the coating and the substrate is propagated with its length depending on the adhesion strength. Experiments carried out with specimens having simulated delaminations confirm that digital speckle pattern interferometry can be used to estimate the delamination length. 相似文献
15.
运用弱散射体产生的部分显现散斑场相位差自由标准偏差的近似表达式,计算和分析了由单会聚透镜成象产生的象平面部分显现高斯散斑场相位差的自由统计性质. 相似文献
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17.
General formulas for the average contrast and probability density function of the sum ofN partially-developed, correlated speckle patterns have been theoretically derived. These two parameters characterizing the
statistical properties of added speckle patterns have been actually evaluated for the sum of two partially-developed, correlated
speckle patterns and shown in figures as a function of the surface roughness of illuminated objects, the wavelength difference
of two illuminating lights, and the number of scattering cells within the illuminated area of objects. 相似文献
18.
19.
The statistical properties of speckle intensity variations produced by coherent light in the far-field diffraction plane of an iluminated area of an object are studied experimentally as a function of the radius of an illuminating beam over the object and are found to have a relation to its surface roughness and correlation lenght. Measurements of the surface roughness and the correlation lenght become possible by investigating the contrast variation of the speckle intensity as a function of the radius of the illuminating beam. 相似文献