共查询到20条相似文献,搜索用时 15 毫秒
1.
本文研究了部分相干光离焦像面散斑的运动规律.激光离焦散斑是其特例.讨论了制约离焦量的因素,并对其实验技术进行了探讨和验证. 相似文献
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It is shown that the fringe shifting technique can increase the sensitivity of speckle photography for sub-speckle size changes.
The technique gives time-ordered pattern that can be used for the sign detection of the motion as well. 相似文献
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A technique has been proposed for the measurement of tilt of a diffuse object using speckle fanning in a photorefractive BaTiO3 crystal. Free space geometry has been used for recording in which the axis of rotation of the object lies away in three-dimensional space. The method is based on recording of two exposures, one before- and another after the tilt, thus producing speckle correlation fringes due to overlapping of two speckle fans. We consider a generalized case of tilt, generating curved fringes with center shifted in the transverse direction. The axis of rotation lies perpendicular to the optical axis in three-dimensional space having the transverse and axial components of the shift in the center of rotation with respect to the diffuser plane. Fourier transform of the curved fringes produces correlation output. Measure of separation between the correlation peaks in transverse and axial directions provides information about the tilt angle, the direction of tilt, and the distance of rotation axis from the optical axis. Experimental results have been presented to validate the theoretical predictions. 相似文献
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Hone-Ene Hwang 《Optics Communications》2009,282(3):351-4360
The theoretical and numerical analysis in this work show that both surface tilting and translational motion can be simultaneously calculated using the speckle photographic technique by recording consecutive speckle pattern images in two different Fresnel diffraction distances. A simulation example based on the proposed scheme is given to verify the method’s validity and high accuracy of the calculated motion detection. Compared with other previous works the results show that this method is efficient and easy to implement. 相似文献
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A new real-time phase-shifting readout system is developed for quantitative evaluation of full-field correlation fringes obtained by means of Fourier filtering in speckle photography. The proposed method, which uses photorefractive crystals as the recording medium, is capable of mapping the whole-field displacement data from the recorded phase-shifted fringe patterns. Experimental results are presented on a diffuse surface subjected to rotation in its own plane. 相似文献
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Rolando Gonzlez-Pea Rosa María Cibrin-Ortiz de Anda Angel J Pino-Velzquez Yhoama Gonzlez-Jorge Rosario Salvador-Palmer 《Optics and Lasers in Engineering》2003,39(5-6):609-618
Speckle photography (SP) is a powerful tool that is adequate to determine small displacements in micrometer range. This information shows other characteristics of structure deformation under loads and can be determined as stress and strain distribution. In this paper we present the results of the application of the SP technique used to study the behaviour of discontinuities in a shearwall model. These structural elements are very important to the stability of buildings. The displacement whole field around the discontinuities and loading points was determined using the pointwise method. This allows us to determine stress distribution at the point of interest by means of the suitable equations. We also present the stress distribution obtained through the finite element method in order to compare the results obtained by means of these two techniques. Good correspondence was found between the displacements determined by both techniques (r=0.982) and also between the stress values we obtained. 相似文献
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旋转孔径白光散斑照相法的研究 总被引:3,自引:1,他引:2
本文报道利用旋转孔径法进行白光散斑照相,研测动态问题.其不仅具有旋转孔径激光散斑照相的优点,而且最突出的优点是能走出实验室,到现场进行动态测量研究. 相似文献
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M.M. El-Nicklawy A.F. Hassan M.E. El-Zaiki T.A. El-Dessouki S.E.-S.Abd El-Ghany 《Optics & Laser Technology》1996,28(7):491-496
The visibility of the speckle pattern resulting from the scattered radiation of transmitted beams through a diffusing surface has been studied for a Gabor hologram and speckle photography. The cases of strictly- and quasi-monochromatic light are also considered. Mathematical expressions for the dependence of the visibility on the distance from the centre of the undiffracted illuminating beam, its spectral half-width Δf and the amplitude ratio m between the reference beam and the integrated scattered beams are obtained. A graphical method is found for determining m and Δf from the visibility as a function of the distance from the centre of the undiffracted illuminating beam. 相似文献
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S. Toyooka Y. Iwaasa M. Kawahashi K. Hosoi M. Suzuki 《Optics and Lasers in Engineering》1985,6(4):203-212
A new method for the automatic processing of Young's fringes in speckle photography is described, based on the technique of spatial phase detection. The amount of calculation is reduced, yet accuracy is of an order comparable with that of the Fourier transform method. Furthermore, orientation of fringes is determined as well as fringe spacing. 相似文献
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We propose three methods for measuring the depth motion (i.e., motion in line-of-sight, not lateral) of bodies with a rough surface by multi-exposure speckle photography. The speckle photographs are processed optically (autocorrelation). The output is a depth-versus-time graph. Two of the three proposed methods have been verified experimentally. The accuracy of the methods can be choosen to be about one wavelength or up to several millimeters. 相似文献
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A photograph of a flow field is taken under laser illumination. If the exposure is short enough, the velocity distribution in the field will be mapped on the photograph as variations in speckle contrast. These contrast variations can be converted to intensity variations by means of a simple spatial filtering technique, to give a direct picture of the velocity distribution in the flow field. A potential application of this technique to the mapping of retinal blood flow is described. 相似文献
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We present a method for studying the lateral motion of a body with a rough surface. A speckle photograph of the moving body is recorded in addition to a still photograph of the same body. The total photograph is then optically Fourier transformed and recorded. Yet another optical Fourier transform yields a display of the motion path (‘trajectory’) of the moving body. 相似文献
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The speckles of the image plane of an object are both radially shifted and decorrelated when the object is axially translated through an amount ?. We demonstrate that this radial shift, which is related to the position of the pupil of the optical system, disappears when the pupil lies in the back focal plane of the imaging lens. However, if the irradiance of the image plane is twice recorded on a photographic plate which is laterally shifted through ζH between the exposures, the minimum value of the contrast of the Fourier fringes exhibited by the plate after processing, gives the value of ? if ? is less than a particular value, ?M which will be defined. Also we propose a new speckle measurement method in which the fringes are automatically removed when ? is greater than ?M. We record the image of the object illuminated in convergent light through an amplitude diffuser placed in the Fourier plane of the object. The mean speckle speckle size of the diffuser is equal to the mean size of the speckles generated by the object in its Fourier plane. 相似文献
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R. Dndliker 《Optics and Lasers in Engineering》1980,1(1):3-19
Holographic interferometry and speckle photography are essentially described by the same equations. The sensitivity and the range of displacements at which the methods are applicable are different however. The accuracy of strain measurement, using high resolution opto-electronic evaluation in both cases, is estimated and compared. 相似文献
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A method for measuring contact pressures based on the measurement of irreversible changes in a surface microrelief by the speckle photography technique is presented. The analytic dependence between the change in the contrast of the carrying Young’s fringes and the relative area of change in the microrelief is considered. An example of a contact interaction between a cylinder end and a flat slab, the latter with a specially produced regular roughness on its contact surface, is used to experimentally verify the relation between the irreversible change in the roughness, the change in the contrast of the holographic interference fringes, and the change in the contrast of the carrying Young’s fringes. It is shown that the sensitivity of correlation speckle photography is higher than the sensitivity of the correlation holographic interferometry technique. 相似文献