<title>Real-time speckle shear photography using BaTiO3 for in-plane strain and displacement measurements at multiple wavelengths</title>
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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 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 moire pattern. The strain is obtained from the width and orientation of the fringes in the moire 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. Time evolution of the growth and the decay of the signal beam also is studied. The above studies are carried out at different laser wavelengths and the results are compared.Keywords:
Moiré pattern
Electronic speckle pattern interferometry is employed in many industrial fields as a useful deformation measurement method. However, two speckle patterns obtained before and after the deformation are necessary for measurement. Furthermore, at least three speckle patterns are required for high resolution measurement using ordinary fringe scanning technologies. In this paper, a novel method that can measure high speed deformations using a limited number of speckle patterns without using high speed cameras is proposed. The method enables application to dynamic deformation analysis because the method involves analysis using only two speckle patterns obtained before and after the deformation. A novel optical system that can record some spatial information into each speckle is set up for the method. In experimental results, it is confirmed that the out-of-plane deformation measurement can be precisely performed by the method and that the resolution power is almost equivalent to that of the ordinary method.
Speckle imaging
Speckle noise
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The speckle interferometry is an effective technique in the displacement measurement of a structure with a rough surface. However, when the fringe scanning technique is introduced to speckle interferometry for improving the measurement resolution, generally two speckle patterns before and after the deformation of the measurement object and another speckle pattern obtained under different conditions from these two speckle patterns are required at least. So, three speckle patterns are generally required for precise fringe analysis as a minimum condition. In this paper, a method for introducing the fringe scanning method is proposed by controlling the phase of the specklegram as a fringe image using filtering techniques. Then, the temporal fringe analysis method that uses only two speckle patterns are proposed for speckle interferometry. As the result of experiments, it is shown that high precise fringe analysis can be realized by the fringe scanning methods using only two speckle patterns for the displacement measurement with a large deformation.
Speckle imaging
Speckle noise
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Digital speckle-pattern interferometry systems for automatic measurement of in-plane deformation of a diffuse object are presented, based on phase shifting of a speckle interferogram. Before deformation, three digital speckle patterns are recorded as changing the phase of reference light such as 0,pi/4, pi/2. After deformation, three digital speckle patterns are recorded with phase shifts - pi/2, 3pi/4, pi, respectively. A calculation of the arctangent with phase-shifted speckle pattern gives the optical path difference which is proportional to the deformation.
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Measurement of Dynamic Characteristics of Structures by the Speckle Interferometry on Single Speckle
- In this article the results associated with the use of speckle interferometry on a single speckle to determine the dynamic characteristics of mechanical constructions are presented. The optical scheme of the speckle interferometer on a single speckle is proposed, which makes it possible to simultaneously record the form and amplitude of the resonant vibrations of mechanical constructions. Theoretical and experimental results demonstrating the behavior of the output signals from the speckle interferometer on a single speckle in the study of the resonant vibrations are presented. The resonance method for measuring the logarithmic decrement of vibrations and other dynamic characteristics of a mechanical constructions using speckle interferometry on a single speckle is proposed.
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Speckle noise
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Developments towards an automatic inspection system based on Electronic Speckle Pattern Interferometry (ESPI) are presented. Emphasis is placed on the techniques for the automatic analysis of the Speckle Pattern correlation fringes to produce three dimensional surface profiles from which various physical parameters can be derived. The range of application and general system design principles will be discussed.
Speckle imaging
Speckle noise
Emphasis (telecommunications)
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Laser speckle limits the resolution that can be achieved in holography. Time- varying speckle is even more troublesome, as it can destroy the coherence needed to record a hologram or the correlation needed to obtain fringes in holographic interferometry. This paper looks at the problems these effects can cause in biomedical holography and at how these problems might be minimized. Applications of the time-varying speckle itself, some already widely used, others more speculative, are also discussed.
Speckle imaging
Speckle noise
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A new method is proposed for the fringe evaluation in electronic or digital speckle pattern interferometry (ESPI or DSPI). A series of interferometric speckle patterns, at least three, are recorded and stored during the deformation of the object. The subtraction of each two of the speckle patterns gives the correlation fringes corresponding to the deformation between the two exposures. These correlation patterns are interrelated. The phase differences between each two exposures can be determined by comparing the phase relationship between these correlation fringe patterns. The method is suitable for dynamic or large deformation measurement. The principle of this method is discussed and the computer simulation and experimental results are given.
Subtraction
Speckle imaging
Speckle noise
Image subtraction
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In this paper a new technology for measuring the dynamic behaviour of structures using the stroboscopic laser speckle interferometry is introduced. A good quality of whole-field speckle fringe patterns and Young's fringe patterns can be obtained when this method is used. Moreover, the methods of identifying the phase information of the vibratory structure and choosing the width of He-Ne laser pulses are discussed. Lastly, it presents the experimental results of comparing the stroboscopic laser speckle interferometry with the time-average speckle interferometry.
Stroboscope
Speckle imaging
Shearography
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In the experimental set-up for measuring temperature fields in fluid flows by using speckle interferometry ( e.g. electronic speckle pattern interferometry or phase shift speckle interferometry ), the part of the; arrangement for the object light beam is just like a subjective speckle photographic system. Therefore, in general, speckle displacements are generated. The speckle displacements can change the intensity distribution of spatial speckle fields. As a result, the intensity distribution of a speckle interferogram is also changed. In this paper the effect of speckle displacements on the speckle interferometry is analyzed and discussed in detail. A physical model and mathematical treatment for the effect are proposed. Experimental results are shown. A method for elimination of the effect is provided. Using the provided method, the temperature measurement error of speckle interferometry can be reduced and the measurement accuracy can also be increased.
Speckle imaging
Speckle noise
Intensity
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A high resolution new fringe analysis method for ESPI with only one camera is proposed by using features of speckle interferometry in a deformation process of a measured object. The profile of intensity of each speckle of the speckle patterns in the deformation process is analyzed by the Hilbert transform. A virtual speckle pattern for creating a carrier fringe image is produced artificially by using the information of profiles of intensities of speckles. The deformation map of the measured object can be detected by the virtual speckle pattern in an operation based on the spatial fringe analysis method. Experimental results show that the difference between the results by the new and the ordinary methods is 0.1 rad as standard deviation. From the results, it is confirmed that the high resolution measurement can be performed by this method the same as compared to the ordinary measurement method which needs to employ three speckle patterns.
Speckle noise
Speckle imaging
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