Formation of speckle interferograms characterizing transverse and longitudinal displacements of a light-scattering surface

The speckle-interferometer sensitivity to transverse or longitudinal displacements of a flat diffusively scattering surface is analyzed for the case of double-exposure recording of a speckle photography. It is shown that the interference pattern characterizing the transverse displacement of a scatterer is localized in the far-field diffraction region, and the interferometer sensitivity depends both on the value and sign of curvature of the spherical wavefront of coherent radiation used in the speckle-photography recording stage. The interference pattern charactering the longitudinal displacement of the scatterer is localized in the near-field diffraction region and in order to record it, spatial filtering of the diffraction field should be performed. The experimental data obtained agree with theory. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 47–54, April, 2007.     

On the lower limit of one beam laser speckle interferometry

It has been customarily assumed that the smallest measurable displacement by one beam speckle interferometry is equal to the smallest speckle size (σ = 1.22 λF) as resolved by the recording camera. In this paper it is shown both analytically and experimentally that the smallest measurable displacement is smaller than the speckle size as it is usually defined.     

Measurement of the off-plane displacement of carbon steel corrosion with twin-object-beam electronic speckle interferometry

In this paper, twin-object-beam electronic speckle interferometry is used to study the longitudinal corrosion of carbon steel. The displacement expression of this technique is deduced and optical fibers are used to reduce the influence of the optical system and improve the quality of speckle pattern. Twin-object-beam electronic speckle interferometry cannot only quantitatively cipher out off-plane displacement as a result of corrosion, but also estimate the change of corrosion speed.     

Speckle interferometry methods for displacement and strain measurements using photorefractive crystal

Photorefractive crystals offer several attractive features such as high resolution and in situ processing. As the images are erasable, these crystals are suitable for read–write applications and hence find potential use in speckle photography, image processing and holography. The barium titanate (BaTiO₃) crystal as recording medium has been extensively used as a novelty filter for real-time in-plane displacement measurements employing two-beam coupling configuration. This paper presents new optical configurations in speckle shear photography to measure in-plan displacement and the strain in real time using BaTiO₃ crystal as recording medium. Speckle photography studies are made using a simple two-beam coupling configuration. In speckle shear photography, a diffused object illuminated with two parallel narrow laser beams is imaged inside the crystal, and a pump beam is added at this plane. The speckle patterns due to each beam and the pump beam produce index gratings. When the object is deformed, the speckle patterns shift consequently. We now have four speckle fields: two generated from the interaction of pump beam with the index gratings and two pertaining to deformed states directly transmitted through the crystal. Thus, the fields from respective points on the object interfere after passage through the crystal and produce the Young's fringe patterns. Due to strain, the fringes in each pattern are of different width and orientation, resulting in the generation of a Moiré pattern. The strain is obtained from the width and orientation of the fringes in the Moiré pattern. The experiments are conducted on a specimen with a notch, which is subjected to tensile loading. The in-plane displacement is measured separately in another experiment. The above studies are carried out at Nd–Yag laser.     

用激光散斑法测盐水溶液浓度的改进

在利用激光散斑法测盐水溶液浓度时,光束透过溶液时会产生不同的纵向位移,但散斑计量对纵向位移不敏感.因此重新设计光路将纵向位移转化为横向位移,实现了溶液浓度的精确测量.     

Cardiac functional analysis by laser speckle interferometry

The laser speckle interference pattern during movement of a rough surface is employed to measure the respective displacements. The purpose of this work is to apply this technique in the form of laser speckle displacement cardiography to analyse the displacement patterns during the I and II heart sounds. The recording is performed by illuminating the chest over the cardiac region by collimated laser beam controlled by an ECG operated electric shutter. By analysis the 3-D displacement patterns are obtained. A comparison shows that the displacement at the apex, right ventricle, aortic and mitral valvular regions are significantly higher during I sound than that of II sound.     

电子散斑归一化互相关法测位移

把粗糙物体表面受到相干光照明时产生的散斑场看作是一个稳态随机信号,在此基础上,本文提出了一种能做到大量程,高精度位移测量的新方法——电子散斑归一化互相关法测位移或称电子散斑照相法测位移.该法实质上是借助数字图像处理技术,通过物体位移前后二个散斑场之间的相关性来进行位移测量方法的发展.文中给出了理论分析和实验系统.实验结果表明,该法有诸如准实时,大量程(毫米级),高精度和线性可靠等优点.     

Spatial filtering of the diffractional field of a double-exposure hologram of a focused scatterer image. Part I

Interferometer sensitivity to a transverse or longitudinal displacement is analyzed for the case of diffusively scattering plane surface. It is shown that the sensitivity does not change when an off-axis spherical reference wave is used instead of a flat one at the stage of hologram recording. However, localization of interference fringes in the Fourier plane, where a pupil image of a positive lens is filtered (the lens was used for recording a hologram of a focused scatterer image), is not accompanied by a parallax phenomenon. In addition, in the case of controlling the longitudinal displacement of the scatterer, the interferometer sensitivity threshold is decreased. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 21–30, August, 2007.     

Optical method for detecting variations of the magnetic field strength

A method of detecting the magnetic field variation is proposed and implemented experimentally. The method employs the rotation of the speckle pattern of light transmitted through an optical fiber that is placed into a longitudinal magnetic field and the recording of a holographic grating in a photorefractive crystal using the speckle field. The possibility of detecting the shape of a 0.15-s magnetic field pulse is demonstrated experimentally.     

Comparison between instantaneous and integral intensities in dynamic speckle pattern interferometry

A new speckle measurement technique called temporal speckle pattern interferometry or time sequential speckle pattern interferometry has been developed recently. Its principle is that by capturing the temporal speckle patterns related to the object deformation or displacement, the whole-field displacement, the amplitude of the vibrating object and the shape of the tested object can be calculated through speckle intensity fluctuation scanning technique or Fourier-transforming method. In this paper, we combine the analytical and numerical methods to simulate the properties of the time demodulation in temporal speckle patterns interferometry techniques. The performance of three kinds of temporal phase sequences, power, exponential and harmonic phase sequences, are studied with the parameters of temporal speckle intensity fluctuation, the value of the spatial phase term, optical integral time of the recording camera and the initial phase of the temporal speckle intensities. The results indicate that the normalized value and period change of the instantaneous intensity are nearly coincident with that of the integral intensity for the harmonic temporal phase sequences and are different for the power and exponential temporal phase sequences.     

Young's modulus measurement of the radius bone using a shearing interferometer with carrier fringes

A technique for measuring Young's modulus of the radius bone by using electronic speckle-shearing pattern interferometry is proposed. The technique is based on the introduction of carrier fringes and the use of a phase unwrapping algorithm to obtain a phase map corresponding to the out-of-plane displacements of a radius bone without sign ambiguities. The carrier fringes are obtained by the correlation algorithm of two consecutive speckle fields with a translation of the illuminating beam between each recording, then the spatial synchronous detection (SSD), an unwrapping phase algorithm and integration process along shear direction are successfully applied for obtaining a displacement phase map. Next, analysis of the radius bone as a cantilever allows us to obtain Young's modulus. The study was performed with speckle interferometry and with the finite element method for comparing the results. Advantages and disadvantages of the proposed method are discussed.     

Use of a joint transform correlator architecture for study of speckle displacements

The optical speckle–displacement correlation technique (OSDCT) is proposed for study of in-plane speckle displacements. The joint transform correlator architecture is used to evaluate the displacements of speckle subimages of strained surfaces. The procedure of the correlation response producing as a result of cross-correlation of strainless and strained surfaces in a conventional joint transform correlator (JTC) is considered. The convenient techniques for a joint power spectrum transformation are selected. The systematic and random errors of a mean speckle pattern displacement of a rigid body motion calculated by using the OSDCT and the digital speckle–displacement measurement technique are compared. The robustness of some JTC versions (a conventional JTC, a JTC with median thresholding, a JTC with subset median thresholding, and a fringe adjusted filter JTC) to input noise of speckle patterns and output noise of a correlation response is studied.     

Multilayer volume holographic optical memory

We demonstrate a scheme for volume holographic storage based on the features of shift selectivity of a speckle reference-wave hologram. The proposed recording method permits more-efficient use of the recording medium and yields greater storage density than spherical or plane-wave reference beams. Experimental results of multiple hologram storage and replay in a photorefractive crystal of iron-doped lithium niobate are presented. The mechanisms of lateral and longitudinal shift selectivity are described theoretically and shown to agree with experimental measurements.     

Formation of interference patterns during double-exposure recording of lens Fourier speckles

Within the Fresnel approximation we consider the formation of a speckle interferogram, sensitive to the inclination of the wave front or the derivative of the normal displacement of the object during its coherent illumination by either a diverging or converging spherical wave. This results in recording a Fourier transform speckle pattern of light diffusely scattered by the surface into the plane of the photographic place. It is shown, both theoretically and experimentally, that the sensitivity varies according to the variation of the Fourier transform scale.V. V. Kuibyshev Tomsk State University. Translated from Izvestiya Vyssikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 100–105, August, 1994.     

Phase-shifting whole-field speckle photography technique for the measurement of in-plane deformations in real time

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.     

Spatial filtering of the diffractional field of a double-exposure hologram of a focused scatterer image. Part II

Analysis is made of the interferometer sensitivity to transverse or longitudinal displacements of a diffusively scattering surface under double-exposure recording of a focused image hologram, where the distribution of the complex field amplitude results from two Fourier transforms of the distribution in the object plane. It is shown that in the case of transverse displacement of the scatterer, the interference patterns are localized in two planes, with each plane characterized by different interferometer sensitivity. In the case of control of the longitudinal displacement, the interference pattern is localized in one plane, however, in order to record it, it is necessary to perform spatial filtering of the diffraction field in the hologram plane. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 78–85, October, 2007.     

散斑场相位涡旋及其传播特性的实验研究

用CCD记录散斑场和参考光的干涉图样, 利用傅里叶变换法实现了散斑场复振幅以及相位分布的实验提取, 在复振幅实部零值线和虚部零值线切点处出现一种新的相位奇点, 与两条零值线交点处的传统相位奇点周围单调螺旋变化的相位分布不同, 绕切点一周的相位具有先增大后减小几乎呈对称性分布的特性, 为了解释这种新的相位奇点,提出了准孪生相位涡旋的概念. 在理论研究散斑场强度的纵向自相关函数的基础上, 实验观察散斑场相位涡旋的传播, 发现在光强纵向相关长度范围内的不同传播距离处的观察面上, 复振幅实部和虚部随机变化而涡旋的 关键词： 相位涡旋 散斑 干涉     

Numerical computation of in-plane displacements and their detection in the near field by double-exposure objective speckle photography

A model of a rough surface to the scale of the optical wavelength is proposed, with randomly distributed zero-mean Gaussian heights. It is assumed that the aforesaid surface is illuminated by a coherent light beam of homogeneous intensity. An in-plane pure translation of this surface is simulated on a PC by means of the Matlab program. In the near-field optical regions the Fraunhofer approximation and the subsequent FFT are not suitable for application in the generation of a speckle pattern. Hence, with the aim of calculating the translation of the rough surface by means of double-exposure objective speckle photography using the point-wise filtering technique (PWFT), the Fresnel-Kirchhoff integral is first employed to obtain the speckle intensity near the surface on a photographic plate, and then the intensity pattern produced by the diffraction of the plate is determined in the far field (Fraunhofer), which suffices to calculate the modulus of displacement through the Young’s fringes. The results are analyzed according to surface roughness and the sample distance to the recording plane.     

Optical mouse digital speckle correlation

The possibilities with which an optical mouse can be applied to obtain scientific measurements are currently limited by the maximum distance possible between the mouse and surface under interrogation. We demonstrate that a simply adapted optical mouse is able to operate as a recording instrument in the digital speckle correlation mode; wherein greater distances between optical mouse and translating surface are possible. Linear (R² > 0.98) and repeatable measurements in the x and y axis were obtained with the optical mouse and translating surface separated at 300 mm. In both cases, the measurement resolution was 0.025 mm. Digital speckle correlation with an optical mouse offers the ability to obtain measurements of displacement and deformation at a fraction of the investment in time and cost of conventional setups.     

Speckle-pattern rotation in a few-mode optical fiber in a longitudinal magnetic field

The process of rotation of a speckle pattern at the output of a few-mode optical fiber in a longitudinal magnetic field is mathematically modeled. It is shown that the deviation from a linear relation between the rotation angle of a speckle pattern at the output of a few-mode fiber and the fiber length in the presence of a longitudinal magnetic field results from a specific dependence of polarization corrections to the propagation constants of TE and TM modes. The calculation results are compared with the results of an experiment on determining the rotation angle of a speckle pattern as a function of magnetic field in a fiber of constant length.