Results of computing unknown phase shift (UPS) errors between synthesized speckle fringe patterns (SFPs) using the population Pearson correlation coefficient (PPCC) are represented. It is shown that mean absolute error of UPS between normalized SFPs is very small over the entire range of phase shifts from 0 to 180 if the RMS height Sq of the 3D rough surface exceeds one seventh of the laser wavelength. These results indicate the possibility of using the PPCC to calculate the UPS in phase shifting digital speckle pattern interferometry.
A method for evaluation of fatigue process zone (FPZ) dimensions near a notch root in metal and alloy specimens by using a two-step phase shifting interferometry (TS PSI) technique is proposed. In comparison with other destructive and nondestructive methods evaluating the FPZ dimensions, it possesses higher accuracy and performance. The method uses a criterion for the FPZ dimensions definition based on an assumption that the surface roughness of notched specimens after cyclic loading reaches its maximum values at the FPZ boundary. To realize this method, first, a phase map (PM) of a total surface relief near a notch root is retrieved; second, roughness and waviness PMs are extracted from the retrieved total surface relief PM by using the TS PSI; and finally, a surface roughness parameter Ra spatial distribution is calculated according to the offered criterion and the FPZ size d* is defined. The FPZ size was measured for specimens made of low-carbon steel and aluminum alloys 2024-Т6 and 7075-T3. Obtained experimental results have shown that the proposed criterion allows defining the FPZ size for notched specimens made of metals and alloys possessing high, moderate, and low plasticity.
A new two-step phase shifting interferometry technique for evaluation of a fatigue process zone (FPZ) in notched metal
and alloy specimens is proposed. In comparison with well-known destructive and nondestructive methods evaluating
FPZ, this technique possesses higher accuracy and performance and allows defining the FPZ size for notched specimens
made of metals and alloys with low, moderate or high plasticity. The technique is fulfilled by retrieval of a total surface
relief of a studied notched specimen, extraction of surface roughness and waviness phase maps from the retrieved surface
relief, calculation of a surface roughness parameter Ra spatial distribution and definition of the FPZ size by using an
extracted surface roughness phase map. Obtained experimental results have confirmed assumption that the surface
roughness of notched specimens after cyclic loading reaches its maximum values at the FPZ boundary. This boundary is
produced as the narrow strip containing pixels possessing the maximum values on the spatial distribution of the
roughness parameter Ra near a notch root. The basic distances d* defining the FPZ sizes were measured for notched
specimens made of a low-carbon steel and aluminum alloys 2024–Т6 and 7075–T3. Results of the distances d*
measurement are very close to respective results obtained with the help of other methods for the FPZ evaluation.
A modified spatial-temporal speckle correlation technique for operational assessment of structural changes in muscle tissues after slaughtering is considered. Coefficient of biological activity as a quantitative indicator of structural changes of biochemical processes in biological tissues is proposed. The experimental results have shown that this coefficient properly evaluates the biological activity of pig and chicken muscle tissue samples. Studying the degradation processes in muscle tissue during long-time storage in a refrigerator by measuring the spatial-temporal dynamics of biospeckle patterns is carried out. The reduction of the bioactivity level of refrigerated muscle tissue samples connected with the initiation of muscle fiber cracks and ruptures, reduction of sarcomeres, nuclei deformation, nuclear chromatin diminishing, and destruction of mitochondria is analyzed.
As a result of optical experiments, it is established that the controlled variation of a recognition sensitivity at the comparison of the input and reference objects can be realized, while solving the recognition task within the method of synthesized phase objects,1 as distinct from the standard approach. We have obtained and analyzed the results of the recognition for a collection of objects with the use a joint Fourier-transform correlator. For each of the objects, we studied the character of the signal amplitude decrease depending on the growth of distortions in the object structure. We show that it is possible to obtain a family of cross-correlation curves that decrease differently within the method of synthesized phase objects, rather than a single curve. This allows one to vary the sensitivity of the correlator in the process of recognition.
A two-step electronic speckle pattern interferometry (ESPI) method with blind phase shift of a reference wave, in which the phase shift extraction is fulfilled by using both a correlation and a discrete Fourier transform (DFT) approaches, is presented here. In the correlation approach, the blind phase shift is calculated via the correlation coefficient between two similar speckle interferograms (SI) differing only by the reference wave phase shift. The DFT approach is based on the blind phase shift extraction from frequency components of SI Fourier spectra. Comparative analysis of these approaches has testified to their high performance. Moreover, it is shown that the correlation approach is more preferable for blind phase shift extraction from SIs with a rough surface than from interferograms with a smooth surface; hence, it is more convenient for ESPI than for phase-shifting interferometry. In addition, this approach provides a lesser level of systematic error of extracted phase shift in comparison with the DFT. The correlation approach was used for experimental definition of Poisson’s ratio for duralumin constructional material by the two-step ESPI method.
Two-frame interferometric method with blind phase shift of a reference wave for smooth surfaces retrieval is
considered. The ability of this method to reconstruct a macrorelief of diffusing surfaces with a given roughness is
studied. Computer simulations have testified the ability of reliable low-noise reconstruction of the diffusing surface
macrorelief with standard deviation of the roughness heights up to λ/10 by using the developed interferogram
processing algorithm. The simulations have shown that the proposed correlation approach, which is used to determine
the reference wave blind phase shift, is more suitable for a diffusing surface than for a smooth one and the increase of
surface roughness leads to a quadruple decrease of this error in comparison with that for the smooth surface.
Experimental verification of the interferometric method performance to retrieve real diffusing surface macroreliefs
with given roughness has been done by using the experimental setup based on a Twyman-Green interferometer and
roughness comparison specimen. The obtained experimental results virtually have coincided with the computer
simulation results that prove the performance of the considered method to retrieve not only smooth, but also diffusing
surfaces.
The optical speckle-displacement correlator based on hybrid optical-digital joint transform correlator architecture with
digital first and optical second stage is used to determine correlation peak position with subpixel accuracy without usage
of intricate interpolation algorithms. Experimental setup for realization of the optical speckle-displacement correlation
technique was constructed on basis of a digital Fourier processor allowing joint power spectrum median and ring median
binarization and an optical Fourier processor. Speckle patterns of steel beam specimen (steel 45) with different maximum
spatial frequencies were recorded. As one of the joint transform correlator main parameters is distance between fringes at
correlator frequency plane, comparison of optical speckle-displacement correlator performance for different values of
speckle pattern maximum spatial frequency for the given joint power spectrum modulation was performed. Experimental
results have shown that the signal-to-noise ratio (SNR) increases steadily while the maximum frequency of speckle
pattern multiplied Fourier spectrum is reaching the Nyquist frequency fN. The analysis of the speckle pattern with
frequencies higher than Nyquist frequency has shown that the SNR growth is continued to the some boundary frequency
fB>fN after which the SNR is fallen sharply. Thus, the influence of aliasing on the correlator performance was studied and
the best correspondence between value of speckle pattern maximum spatial frequency and distance between fringes at
the correlator frequency plane was found.
The optical speckle-displacement correlation technique was developed to increase the reliability of surface displacement
field recovery near stress concentrators. The performance of optical speckle correlators based on joint transform correlator
(JTC) architecture and a joint power spectrum nonlinear filtering (median thresholding, adaptive median thresholding,
ring median thresholding) is studied by using computer models of these correlators. The design of hybrid joint transform
speckle correlator is detailed. Example results of correlation signal using computer models of digital speckle correlation
and optical speckle-displacement correlation techniques and created hybrid joint transform speckle correlator setup are
described.
The new approach for creation of film reflecting holographic marks for optical security is proposed. Such marks are replicas of a reflecting master hologram recorded on a chalcogenide glass layer. To receive the master hologram, the joint power spectrum of an input phase mask or a transformed phase mask and a reference phase mask is produced at the plane of the hologram writing and is modulated by an inclined laser beam. If an inclined laser beam illuminates the replica recorded on a flexible substrate, phase noise including speckle noise is eliminated because the hologram carrier frequency exceeds greatly the limiting frequency of the phase noise power spectrum. Experimental results have shown the principal possibility to produce the high performance film reflecting holographic marks for security applications. The proposed approach can be combined with technologies for fabrication of rainbow holograms. In this case, the received rainbow holograms are the reflecting holographic marks simultaneously. Therefore, they can be verified not only visually, but also by means of automatic identification.
The new reflecting optical mark is created. This mark has been received by recording of a joint power spectrum (JPS) of a transformed and reference phase masks on a chalcogenide glass As40S40Se20. In order to fabricate the reflecting optical mark, we must choose the optimum exposure of its writing. We have offered the procedure for calculation of such exposure by using the experimental dependence of diffraction efficiency as a function of a chalcogenide glass layer exposure and the analytical equation for the JPS of two phase masks containing rectangular phase elements. This procedure includes the calculation of the correlation peak relative intensity as a function of the JPS interference pattern frequency band that is read by laser beam, and calculation of the dependence "peak relative intensity versus exposure." The proposed reflecting marks allow realizing the quantitative estimation of a secured product authenticity due to producing of a correlation field and realization of the mark's identification procedure. The experimental setups based on an optical Fourier processor architecture were created for writing of reflecting optical marks and their reading and identification. The experimental examinations of dependency between a peak-to-noise ratio and exposure of a chalcogenide glass layer for the series of fabricated reflective marks were carried out. The obtained results were compared with theoretical results.
The comparative analysis of the digital speckle-displacement measurement technique and the optical speckle-displacement correlation technique is carried out. Some versions of a joint transform correlator (JTC) architecture, namely a conventional JTC, a JTC with median thresholding, a JTC with subset median thresholding, and a fringe adjusted filter JTC, are used for study of in-plane rigid body displacements. The systematic and random errors of speckle pattern's mean displacement calculated by using the mentioned above techniques are compared. The robustness of the digital speckle-displacement measurement technique and four JTC versions to input noise of speckle patterns and output noise of a correlation response is studied.
The new method for identification of optical marks containing transformed phase masks (TPMs) is considered. A TPM placed in an optical correlator produces several sharp correlation peaks on its output. We choose the distances between peaks as basic geometrical features of a TPM. The increase of quantity of basic features leads to the increase of security level of documents and valuable papers. However, the amount of such features is limited and is depending from many factors. We picked the probability of false identification of the nearest feature as the criterion of separation of features on independent classes. The optical/digital device for identification of credit cards based on a joint transform correlator architecture was used for the study of TPMs. To estimate the law of distribution of basic features inherent to the same class, we carried out experiments with the series of TPMs. We have shown, that the additional features allow to increase the number of basic features, separated on different classes. These experiments also have allowed to estimate the error of features measurements
The new optical security technique based on usage of the TPM is developed. The created experimental setups and optoelectronic device have proved the performance of this technique for security verifications of credit cards and other documents and products.
Use of security devices based on a joint transform correlator (JTC) architecture for identification of credit cards and other products is very promising. The experimental demonstration of the random phase encoding technique for security verification shows that hybrid JTCs can be successfully utilized. The random phase encoding technique provides a very high protection level of products and things to be identified. However, the realization of this technique is connected with overcoming of the certain practical problems. To solve some of these problems and simultaneously to improve the security of documents and other products, we propose to use a transformed phase mask (TPM) as an input object in an optical correlator. This mask is synthesized from a random binary pattern (RBP), which is directly used to fabricate a reference phase mask (RPM). To obtain the TPM, we previously separate the RBP on a several parts (for example, K parts) of an arbitrary shape and further fabricate the TPM from this transformed RBP. The fabricated TPM can be bonded as the optical mark to any product or thing to be identified. If the RPM and the TPM are placed on the optical correlator input, the first diffracted order of the output correlation signal is containing the K narrow autocorrelation peaks. The distances between the peaks and the peak's intensities can be treated as the terms of the identification feature vector (FV) for the TPM identification.
The possibilities of using of optical and hybrid joint transform correlator (JTC) architectures for construction of security devices with usage of the transformed phase masks (PMs) as optical marks are investigated. With this purpose the yardsticks of an estimation of their efficiency, namely peak- to-noise ratio (PNR) and relative intensity of correlation peaks, are selected general for two types of JTCs. The idealized model of an interference noise in a linear JTC is designed, if the binary random PMs on input are entered. The relations of a PNR to dimension both PM and window ambient correlation peak are parsed. The optically addressed spatial light modulator (OASLM) based on the chalcogenide glass photoconductor -- nematic liquid crystal structure is studied. The experimental setup of an OASLM JTC is designed on the basis of this SLM. The relations a PNR and relative intensity versus an effective focal length are studied and the major factors limiting efficiency of the setup are parsed. The optoelectronic device based on a hybrid optical-digital JTC architecture is built. The relations to different conditions of a joint power spectrum recording by a CCD-camera in this device are investigated. The comparative analysis of two types of JTC is carried out also concluding about expediency of their usage for different security applications is made.
The procedure for identification of a random phase mask in a nonlinear joint transform correlator containing a photosensitive recording material or a spatial light modulator in a frequency domain is studied. The new approach for estimation the intensities of correlation peaks in such type of a nonlinear correlator is proposed. This approach is based on the use of an experimental dependence of the recording medium's diffraction efficiency versus its exposure. The comparative analysis of correlation peaks produced by phase masks and primary test images in nonlinear joint transform correlators containing different photosensitive recording medium in frequency domains is represented. The results of analysis have shown, that the peak intensities produced by phase masks and by primary images are the same in a linear joint transform correlator, but the peak intensity produced by a phase mask in the nonlinear joint transform correlator is much larger than the peak intensity produced by a primary image.
The hybrid optical-digital two-stage joint transform correlator (JTC) experimental setup was created. The transformed phase mask (PM) was used as an optical mark to be identified in the hybrid JTC. The minimum possible focal length of a Fourier lens in the joint Fourier transform processor of the hybrid JTC first stage was defined and optical schemes were calculated and designed. The procedure of the transformed PM identification in the hybrid JTC was represented. Performance of transformed PMs in different modifications of the experimental setup was studied. The peak-to-noise ratio (PNR) for each correlation peak in the firs diffraction order of the output correlation signal was calculated. The dependencies PNR versus effective focal length were analyzed.
The hybrid optical-digital joint transform correlator (HJTC) experimental setup was created. The minimum focal length of a Fourier lens in the joint Fourier transform processor (JFTP) was found. The procedure of the transformed phase mask (PM) identification in the HJTC was represented. A several modifications of the setup with different effective focal length of the JFTP were used for investigations of transformed PMs. The peak-to-noise ratio (PNR) for each correlation peak in the first diffraction order of the output correlation signal was selected as the objective criterion of the transformed PM identification performance. The performance of the transformed PMs identification in the HJTC was studied. The dependencies PNR versus effective focal length of a JFTP were analyzed. The influence of the CCD-camera recording aperture relative dimensions on degradation of correlation peaks was studied.
The security verification method using a transform random phase mask as an optical mark bonded to a document or other product is proposed. This mask consists of separated and shifted fragments of a reference phase mask. If the transformed and the reference masks are entered into an optical correlator, the autocorrelation peaks series is produced on the correlator output. The distances between peaks and the peak intensities were used to produce the feature vector. Identification of the document or other product takes place if the feature vector and the reference feature vector coincide. The procedure of the transformed mask generation and the process of the peaks' producing in a conventional joint transform correlator were considered. The advantages of transformed mask applications in optical correlators are discussed. The joint transform correlator experimental setup containing the spatial light modulator PRIZ was designed and the optimal conditions to produce the autocorrelation peaks were found.
KEYWORDS: Optical signal processing, Acousto-optics, Optical components, Optoelectronics, Signal processing, Data processing, Photodetectors, Phase shifts
Application of acousto-optical cells in optoelectronic systems for signal processing allows to realize a high-speed data input and to provide the real-time signal optical processing. The nature of acousto-optical cells permits to realize the processing of only one dimensional data massive. But principal possibility of hybrid optoelectronic systems creating for two dimensional data massives processing exists. We propose to utilize the optical astigmatic element in an acousto-optic device for obtaining the simultaneous time delay and frequency multichannel processing. For this purpose we create the acousto-optic device for spatial data processing on the base of acousto-optic cells in the combination with matrix-array photodetector and special phase shift optical element. Investigation of the acousto-optic device characteristics is carried out.
The input image phase encoding method is utilized for identification of random binary phase masks (RBPM) and their separated fragments with a joint transform correlator (JTC). Equations for a joint power spectrum of a reference RBPM and its separated fragment and for a fragment's autocorrelation function produced in a JTC are obtained. Dependences between separated mask's fragment parameters and autocorrelation output signals are determined. Equations for autocorrelation peaks coordinates definition at a JTC output plane are found. Computer simulations of a mask's fragments autocorrelation functions are carried out. Influence of a mask and a fragments dimensions on output autocorrelation and sidelobe peaks is studied on a base of obtained results. Algorithm for realization of a code identification by a JTC with a phase-encoded input is proposed
The model of the robot vision system for image centering contained the joint transform correlator (JTC) with a phase-encoded input is proposed. The algorithm for an image centering and tracking realized with the robot vision system is considered. The principle of the image tracing algorithm is discussed. The theoretical analysis of the proposed system for the phase-encoded binary rectangular image entered to the JTC input is carried out. Equations for calculation the autocorrelation peaks and differential signal at the JTC output are obtained. Dependencies between geometric parameters of the moving phase-encoded input image and output signal magnitudes are found. Possibilities of the proposed system for a scale- and rotation-invariant object centering are briefly considered.
The model of the real-time scale-rotation invariant joint transform correlator (JTC) was proposed. The pattern recognition algorithm realized by this correlator was developed. The information-dynamic characteristics of the JTC's input device contained the TV-tube and the joined liquid crystal spatial light modulator are studied. The experimental setup of the JTC for binary image recognition was created. The optimum working modes of the constructed correlator were found. The possibilities of the JTC's experimental setup for the finger-print pattern recognition were investigated.
The analysis of the random binary phase mask's (RBPM) power spectrum and correlation functions was carried out. The equations for correlation functions and correlation peaks of the RBPM at the output plane of the coherent optical correlator are obtained. Narrowing of the RBPM's correlation peaks to the sizes of the RBMS pixels is studied. The level of background noise surrounding the correlation peak is estimated and the signal-to-noise ratio is defined. The decoding (recognition) probability of the arbitrary RBPM or the phase-encoded image in the coherent optical correlator is evaluated. The joint transform correlator (JTC) with a liquid crystal spatial light modulator placed in the spectral plane of the JTC was created for experimental proving of obtained results. The sufficient increase of the phase-encoded images correlation peaks in this JTC was observed and explained. Supposition about phase encoding of images in retina of a biological vision system for explanation of high recognition ability of vital organisms is proposed.
The capabilities of the hybrid optical/digital system for nondestructive testing of high- temperature melts, liquid metals, and liquids by sessile drop method were studied. The spatial- temporal noises and spatial (geometric) noises of the system were analyzed and measured. The spatial-temporal noise caused by sessile drop's lateral oscillation were marked and measured. The experimental dependencies between noises variances and relative illumination of sessile drop images are obtained. The functional connection between the maximum variance of the sessile drop's random lateral oscillation noise and the surface tensions of studied substances was found.
The optical/digital system with solid state array detectors for capillary characteristics of materials and high-temperature melts measuring and diagnostics by sessile-drop method is described. Conditions of sessile drop image forming in the optical scheme of the system are defined. The spatial gradient algorithm for image spatial gradient field forming and gradient maximums localization is proposed. Three methods of sessile drop geometric parameters precise measuring and gradient maximums locations estimation are described. The results of distilled water and mercury sessile drop geometric parameters multiple measurements with the subsequent averaging of obtained data are presented. The perspectives of measurement accuracy increasing and sessile drop image processing time decreasing are discussed.
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