Digital phase-shifting shearography for slope measurement

A method is proposed for checking the reliability of a quantitative estimate of longitudinal displacements in metallic beam samples when they are investigated by electronic speckle interferometry and phase-shifting speckle interferometry. Theoretical and experimental results are presented for the investigation of longitudinal surface displacements of samples by electronic difference speckle interferometry and phase-shifting speckle interferometry. © 2004 Optical Society of America

It is shown that the speckle nature of electronic speckle pattern interferometry images can be reduced in quasireal time with the use of only three consecutive video images. By use of additive-subtractive phase modulation processing the technique is essentially insensitive to environmental noise, and distortion of fringes does not occur. By further removing the random speckle phase we show, using speckle statistics, that the number of dark speckles in the resulting fringe pattern is close to zero.

Video-based speckle interferometric methods such as electronic speckle pattern interferometry (ESPI) allow us to measure full-field surface deformation of a diffuse object. In this paper we show, in a first step, that the susceptibility of ESPI to noise can be substantially reduced [1] by synchronizing the optical interferometer and the object stressing system with the CCD image acquisition and processing system, and by performing what amounts to a repetitive sequence of rapid ESPI tests. In this manner, a stable fringe pattern can be obtained as long as the ambient noise is of sufficiently lower frequency than the video acquisition rate (typically 30 Hz). This scheme will be referred in this paper as reference-updating subtractive correlated ESPI to distinguish it from classical ESPI. We then take this issue further with a hybrid additive-subtractive decollated ESPI technique that will freeze out unwanted environmental noise of frequencies much higher than video rates [2], The basic principle of this proposed technique can be summed up as follows: (i) acquire speckle images containing information about the same two deformed object states in every frame of the image acquisition sequence, (ii) decorrelate the speckles between every frame, and (iii) compare every consecutive pair of speckle images to extract visible fringes corresponding to the two deformed states of the test object.

A novel interferometric method for contour mapping of optically rough surfaces

The atmosphere of the earth restricts the resolution of conventional astrophotography to about 1 arcsec. Much higher resolution can be obtained by using speckle methods. The speckle masking method (triple correlation method) yields images of general astronomical objects with diffraction-limited resolution, for example, 0.03 arcsec resolution for a 3.6-m telescope. True images are obtained since speckle masking reconstructs both the modulus and the phase of the object Fourier transform. Therefore, speckle masking is a solution of the phase problem in speckle interferometry. The limiting magnitude of speckle masking is about 20m. Speckle spectroscopy is a speckle method that yields objective prism spectra with diffraction-limited angular resolution. Finally, speckle masking can recon-struct high-resolution images from optical long-baseline interferograms. A 1-km telescope array on the earth would yield images with 10 arcsec resolution. With a 40-km array in space a fantastic resolution of 10^-6 arcsec can be achieved at λ-200 nm. We show speckle masking observations of NGC 3603 and Eta Carinae and computer simulations of optical aperture synthesis.

We propose a small angle measurement setup that utilizes the electronic speckle pattern interferometry (ESPI). By leveraging different principles within the same device, this method achieves complementary advantages across various angle ranges, enhancing measurement accuracy while maintaining high robustness. By utilizing CCD to record light field information in real-time and combining geometric and ESPI methods, relationships between small angles and light field information are established, allowing for the design of relevant algorithms for real-time angle measurement. Numerical simulations and experiments were conducted to validate the feasibility and practicality of this method. Experimental data show that the geometric method achieves a measurement accuracy of 4.39" and a resolution of 1.828" within a measurement range of 54" . In contrast, the ESPI method demonstrates a higher accuracy of 0.43" and a finer resolution of 0.284", with a theoretical measurement range of up to 0.6∘. In an angle measurement experiment with a maximum angle of approximately 0.1∘, the combined application of both methods achieved a measurement accuracy of 7.68" and a resolution of 3.75". This approach effectively compensates for the limitations in measuring small angles over a large angular range, demonstrating significant potential for applications in precision measurement, optical testing, and related fields.

TV-Holography and holographic interferometry: Industrial applications

Carburizing is widely used to improve wear resistance and fatigue life of high duty machine parts. Fatigue performance of the carburized components is greatly dependent on the residual stress state in the surface layer. The aim of this paper is to measure the depth profiles of residual stresses in the carburized steels by electronic speckle laser interferometry (ESPI) assisted hole-drilling, and to compare the results with those measured by X-ray diffraction technique. To comprehend the differences in the residual stress state, the low-C steel components were carburized, and then, tempered in the range of 180–600 $$^{\circ }$$ C. Microstructural investigations and hardness measurements were also conducted. The results obtained from both techniques gave identical results, and showed that the beneficial compressive residual stresses exist at the surface after carburizing, and their magnitudes decrease with increasing tempering temperature. It was concluded that ESPI assisted hole-drilling, with optimized drilling and stress calculation parameters, is suitable for determining the residual stress state of the carburized and tempered steels.

Electronic Speckle Pattern Interferometry (ESPI) is becoming a very common test and measurement tool among industrial users. In its present form it rivals any current techniques for speed and ease of use. With improvements in image quality it has the potential to become the definitive tool for non-destructive testing.

The atmosphere of the earth restricts the resolution of conventional astrophotography to about 1". We will discuss various high-resolution speckle methods which can overcome image degradation caused by the atmosphere and telescope aberrations. All methods yield diffraction-limited resolution, for example 0.03" for a 3.6m telescope. We will show various astronomical applications of speckle interferometry, observations of asteroids, Pluto/Charon, double stars and the gravitational-lens triple quasar. Speckle interferometry can yield a true diffraction-limited image if there is a point source (reference star) in the isoplanatic neighbourhood of the object (holographic speckle interferometry). We show an application of holographic speckle interferometry to the central object R136a of the 30 Doradus nebula in the Large Magellanic Cloud. A true diffraction-limited image of R136a has been reconstructed. The image shows that R136a consists of 8 stars. Speckle masking is a triple correlation method which yields diffraction-limited images of general astronomical objects. A point source near the object is not required. We will describe an application of speckle masking to the central object in the giant H II region NGC 3603. The reconstructed image shows that this central object is a star cluster of 4 stars with magnitudes 11m, 12m, 13m and 13m. The signal-to-noise ratio of the speckle masking image is about the same as the signal-to-noise ratio of the speckle interferometry autocorrelation. Speckle spectroscopy is a speckle method which yields diffraction-limited objective prism spectra. It is also possible to apply speckle masking to multiple-mirror interferometers or long-baseline interferometers on the ground or in space. True images of very high angular resolution can be obtained by these techniques. We will show computer simulations which illustrate the dependence of the signal-to-noise ratio on photon noise.

The study of orbital parameters of multiple Ap stars may lead to new suggestions about the origin and magnetic properties of the components. 53 Cam is one of the best studied binaries among Ap stars. However, the nature of its secondary star remains unclear despite the wealth of spectroscopic observations. The system was first directly resolved by speckle interferometry method in 1980 at the 4 m KPNO telescope McAlister et al. (1983). The authors supposed that the magnitude difference between the components could be close to zero. From that time, 16 speckle measurements of the system were made, including 7 observations collected with the SAO 6 m telescope. In addition to relative positions of the components, speckle observations from the 6 m telescope provide high accuracy magnitude difference estimates.To search for other articles by the author(s) go to: http://adsabs.harvard.edu/abstract_service.html

A measurement method based on dual-channel speckle interferometry is proposed for the quantitative detection of internal defects in structures. The approach integrates digital speckle pattern interferometry and digital shearography (DS) to measure both out-of-plane displacement and its first-order derivative under single loading. On one hand, DS preliminarily evaluates defect boundaries, laying the foundation for subsequent defect boundary characterization. On the other hand, the combination of the continuous wavelet transform and the gradient streamline method enables complete boundary detection of hidden singularities in the out-of-plane displacement field. Finally, simulations and experiments demonstrate that the proposed method offers significant advantages in the detection of internal defects and the suppression of noise in speckle interferometry.

The transient over-voltage in the railway network will endanger the normal operation of the railway. The contactless electric field sensors can measure it flexibly and conveniently and plays an important role in analyzing the characteristic parameters of the overvoltage and designing the insulation coordination of the railway. While in contactless measurement of two-phase voltage, the electric field measured by the sensor placed under the line is the coupling electric field produced by two-phase conductors with different proportion coefficient. Therefore, a decoupling method of contactless electric field measurement for railway catenary is proposed. Through this method, the proportion coefficient of electric field generated by each phase conductor at each sensor can be calculated, and the two-phase voltage can be inversely deduced from the measured two-phase electric field signal. Finally, the voltage measurement test is carried out in the traction substation. The research results can provide guidance for contactless voltage measurement of traction power supply catenary.

Field measurement is a major method for studying issues related to the outdoor thermal environment. Through accurate acquisition and objective analysis of the measured data, the rule of dynamic physical parameters can be obtained. This paper analyzes the outdoor thermal environment researches carried out in China and overseas in recent years and puts the emphasis on field measurement at fixed points. Conclusions include a summary of three types of arrangement methods of measuring points based on multi-variable control method, pre-analysis method and lumped parameter method. Besides, two types of ways to improve the reliability of measurement results are also given. Finally, relevant suggestions for the future standardization for measuring methods of outdoor thermal environment are put forward.

The work is devoted to the application of an artificial neural network (ANN) to analyze eigenfrequencies of personal tires of different construction. Experimental measurements of personal tire eigenfrequencies by electronic speckle interferometry (ESPI) are compared with those previewed by ANN. Very good agreement of both data sets is presented.