Displacement Of Fringes Research Articles

Grayscale-phase calibration of liquid crystal spatial light modulator with vortex-grating lateral-shearing interferometry

Abstract Liquid crystal spatial light modulators (LC-SLMs) are widely used in optics, and grayscale-phase calibration can effectively improve their modulation accuracy. The most commonly used grayscale-phase calibration method is based on the displacement of interference fringes, which is susceptible to environmental interference and only uses a part of the LC-SLM area. In this paper, vortex-grating lateral-shearing interferometry is introduced into the grayscale-phase calibration, which can theoretically obtain the phase information of the full pixel on the LC-SLM. The self-reference experiment not only carries out the grayscale-phase calibration, but also proves the effectiveness of our proposed method by Twyman-Green interferogram between the reference beam and the vortex beam produced by LC-SLM. High-precision grayscale-phase calibration of LC-SLM can open up some new application scenarios in the future.

Deep-learning approach to measuring the refractive index of transparent liquids.

A deep-learning approach is introduced to determine the refractive index of transparent liquids based on variations in the displacement of ultra-smooth interference fringes. The phase characteristics of these fringe variations captured in video data were analyzed and modeled using group-phase fitting. A neural network model, integrating a dense convolutional network with a long short-term memory network, was then developed and trained for high-precision liquid refractive index measurements. Experiments demonstrated an R2 accuracy of 99.70% and a mean squared error of 0.0003. This methodology has been confirmed to be temperature-dependent, considerably stable against external disturbances, highly accurate, and capable of real-time processing.

Determining ion mobility in perovskite films using the running fringes method

This study provides theoretical and experimental evidence that the voltage generated in perovskite films by interference fringes' motion at low velocities can be used as a tool for assessing ions' electric mobility in these materials. We introduce a theoretical model for running fringe (RF) photo-electromotive force (EMF) in bipolar semiconductors, which considers the effects of mobile ions. This model leads to an analytical expression for the dispersion relation of space charge waves in the presence of mobile ions. Notably, it predicts a peak in the RF photo-EMF voltage when the velocity of fringe displacement matches the ion velocity in the photo-induced space charge field. To validate this, we conducted RF photo-EMF measurements on thin films of the methylammonium lead iodide semiconductor. The observed experimental dependencies align closely with theoretical predictions, and the determined values of ions' electric mobilities and activation energies are consistent with those previously reported in the literature.

Fabry-Perot Interferometer Used to Measure Very Low Static Pressure Measurements.

This paper describes the use of an optical instrument, the Fabry-Perot interferometer, adapted to measure very low pressures. The interferometer consists of two high-reflectance flat mirrors placed one in front of another. In addition, a metallic chamber contains air or a gas. In one of the faces of the chamber, a flexible thin silicone membrane is attached and, over it, one of the mirrors is glued. The other mirror rests in a fixed mechanical mounting. Light crosses both mirrors and, when it leaves them, forms an interference pattern consisting of concentric circular fringes. When the pressure is increased/decreased within the chamber, a displacement of the fringes is observed due to the movement of the glued mirror. By measuring the fringe displacement and knowing the pressure, a calibration plot can be made. Minimum pressure measurements of about tens of Pascals were achieved.

Fiber Loop Mirror Based on Optical Fiber Circulator for Sensing Applications

In this paper, a different Fiber Loop Mirror (FLM) configuration with two circulators is presented. This configuration is demonstrated and characterized for sensing applications. This new design concept was used for strain and torsion discrimination. For strain measurement, the interference fringe displacement has a sensitivity of (0.576 ± 0.009) pm‧με-1. When the FFT (Fast Fourier Transformer) is calculated and the frequency shift and signal amplitude are monitored, the sensitivities are (-2.1 ± 0.3) × 10-4 nm-1 με-1 and (4.9 ± 0.3) × 10-7 με-1, respectively. For the characterization in torsion, an FFT peaks variation of (-2.177 ± 0.002) × 10-12 nm-1/° and an amplitude variation of (1.02 ± 0.06) × 10-3/° are achieved. This configuration allows the use of a wide range of fiber lengths and with different refractive indices for controlling the free spectral range (FSR) and achieving refractive index differences, i.e., birefringence, higher than 10-2, which is essential for the development of high sensitivity physical parameter sensors, such as operating on the Vernier effect. Furthermore, this FLM configuration allows the system to be balanced, which is not possible with traditional FLMs.

Fringe Detection and Displacement Sensing for Variable Optical Feedback-Based Self-Mixing Interferometry by Using Deep Neural Networks

Laser feedback-based self-mixing interferometry (SMI) is a promising technique for displacement sensing. However, commercial deployment of such sensors is being held back due to reduced performance in case of variable optical feedback which invariably happens due to optical speckle encountered when sensing the motion of non-cooperative remote target surfaces. In this work, deep neural networks have been trained under variable optical feedback conditions so that interferometric fringe detection and corresponding displacement measurement can be achieved. We have also proposed a method for automatic labelling of SMI fringes under variable optical feedback to facilitate the generation of a large training dataset. Specifically, we have trained two deep neural network models, namely Yolov5 and EfficientDet, and analysed the performance of these networks on various experimental SMI signals acquired by using different laser-diode-based sensors operating under different noise and speckle conditions. The performance has been quantified in terms of fringe detection accuracy, signal to noise ratio, depth of modulation, and execution time parameters. The impact of network architecture on real-time sensing is also discussed.

Decision-making fusion of InSAR technology and offset tracking to study the deformation of large gradients in mining areas-Xuemiaotan mine as an example

The multi-level disturbance of underground and surface caused by coal mining activities intensifies the deterioration of the ecological environment in the mining area. Among them, the uneven settlement caused by coal mining is the most intuitive manifestation of surface environmental damage. The uneven settlement in the mining area has the characteristics of large settlement magnitude and severe deformation. Therefore, based on 15 Sentinel-1A image data, this paper uses three methods: SBAS InSAR, continuous D-InSAR and offset tracking technology to monitor the surface deformation of the mining area. The results show that the continuous D-InSAR technology SBAS-InSAR technology is applied to the small deformation in the edge area of the subsidence basin. The mining area with low gradient subsidence of SBAS-InSAR can obtain better performance than continuous D-InSAR technology. The offset tracking technique is used to monitor the large gradient deformation in the center of the subsidence basin. Therefore, this paper proposes to expand the quantitative analysis through the spatial coherence threshold and the accuracy and successful image elements of the interference fringe displacement. Combine the advantages of the three methods and overcome the shortcomings of each method, fuse the deformation information of the three methods, and obtain the deformation law of the whole surface subsidence. The results show that the mean absolute error (MAE1-1) of continuity D-InSAR is 0.92 m, the mean absolute error (MAE2-1) of SBAS-InSAR is 0.94 m, and the mean absolute error (MAE3-1) of Offset-tracking is 0.25 m. The results of this fusion method are in good agreement with the measured data, and the mean absolute error (MAE4-1) of vertical displacement is 7 cm. Therefore, the fusion method has advantages over individual methods and provides a new idea in monitoring the large gradient deformation of coal mining subsidence in mining areas.

3D velocity and temperature distribution measurement and characteristic analysis of swirling combustion

The latest research directions of combustion flow field visualisation and combustion diagnosis have been extended to the development of non-contact, multi-parameter measurement methods for qualitative analysis and multi-dimensional visualisation. Velocity and temperature are important parameters that reflect the characteristics of the combustion flow field and affect the combustion dynamics and combustion mechanism, which have become the keys to characterising and diagnosing the combustion process. Three-dimensional (3D) velocity and temperature fields of combustion were reconstructed in combination with particle image velocimetry (PIV) and deflection tomography temperature measurement methods, and swirl combustion characteristics were studied. A non-premixed burner was designed to generate a swirling flame, and an experimental system was constructed for the simultaneous measurement of velocity and temperature to acquire tracer particles and Moiré fringe images. A 3D particle recognition technology and cross-correlation algorithm were used to reconstruct a 3D combustion velocity field. The fringe displacement analytical technique and deflection angle correction iterative tomography algorithm were used to reconstruct a 3D temperature field. The effects of different swirl numbers and swirl vane positions on the characteristics of the swirl flame shape, velocity distribution, and temperature distribution were investigated. The combustion reaction and field process evolution were explained. Certain characteristics, including heat and mass transfer and flow field transport of swirling combustion, were analysed. The measurement errors were discussed.

Comparison of stress separation procedures. experiments versus theoretical formulation

The article deals with stress separation using different experimental techniques and their comparison to numerical and theoretical solutions. The method is applied to a keyhole sample coupon, to which measurements of fringe order, temperature or displacement were made using photo-elasticity, TSA (Thermo-elastic Stress Analysis) and DIC (Digital Image Correlation). The results are compared to FEM simulations (Finite Element Method) using the stress concentration factor (Kt) as a benchmark. Additionally, an Airy stress function is proposed and tested against obtained measurements. The comparison of Kt shows agreement among measurements as well as numerical and theoretical results. It is concluded that the presented method can be used for isotropic materials subjected to the plane stress, where stress variation through-thickness is negligible.

Determination of the Spatial Resolution in the Case of Imaging Magnetic Fields by Polarized Neutrons

One of the most important parameters characterizing imaging systems (neutrons, X-rays, etc.) is their spatial resolution. In magnetic field imaging, the spatial resolution depends on the (magnetic) resolution of the depolarization of spin-polarized neutrons. This should be realized by different methods, but they all have in common that a spin-polarizing and spin-analyzing system is part of the resolution function. First a simple and useful method for determining the spatial resolution for unpolarized neutrons is presented, and then methods in the case of imaging with polarized neutrons. Spatial resolution in the case of polarized neutron imaging is fundamentally different from ‘classical’ spatial resolution. Because of π-periodicity, the shortest path along which a spin-flip can occur is a measure of ‘magnetic’ spatial resolution. Conversely, the largest detectable magnetic field (B-field) within a given path length is also a measure of magnetic spatial resolution. This refers to the spatial resolution in the flight direction of the neutrons (Δy). The Δx and Δz refers to the spatial resolution in x- or z-direction; however, in these cases a different method must be used. Therefore, two independent methods are used to distinguish longitudinal and lateral spatial resolution, one method to determine the modulation transfer function (MTF) by recording the frequency-dependent fringe contrast of magnetic field images of a coil (longitudinal spatial resolution), and the second method, to observe the fringe displacement at the detector as a function of magnetic motion, provided that the accuracy of the motion is much better than the pixel size (at least half the pixel size) of the detector (lateral spatial resolution). The second method is a convolution of the fringe pattern with the pixel array of the detector.

Geometric-phase polarimetry

This paper describes polarimetric strategies based on measuring the light’s geometric phase, which results from the evolution of the polarisation state while traversing an optical system. The system in question is described by a homogeneous Jones matrix, which by definition, contains mutually perpendicular eigenpolarisations. Our leading theory links the system’s Jones matrix parameters (eigenvalues and eigenvectors) with the input polarisation state and the geometric phase. We demonstrate two interferometric techniques. The first one measures the geometric phase based on the relative lateral fringe displacement between the interference pattern of two mutually-orthogonal polarisation states. The second technique uses the visibility of the interference fringes to determine the eigenpolarisations of the system. We present proof-of-principle experiments for both techniques.

Formation and Outburst of the Toguz-Bulak Glacial Lake in the Northern Teskey Range, Tien Shan, Kyrgyzstan

In Kyrgyzstan, outburst flood disasters from glacial lakes are increasing. An example is the sudden drainage on 8 August 2019 of the Toguz-Bulak glacial lake in the Tosor river basin of the northern Tien Shan region. In this study, we used remote sensing and field surveys to examine the reasons for the outburst. We found that the lake area changed from 0.021 km² to 0.002 km2 due to the outburst, in which most of the initial 130,000 m3 of water discharged within four hours. In examining the longer-term behavior of this lake, we found that from 2010 through 2019, it appears in June and disappears in September every year. Its maximum area occurs in late July and early August. With the expansion of the lake basin between 2010 and 2019, the lake also increased greatly in size, particularly so in the three years before the outburst, linked to high summer temperatures and the resulting higher inflow of glacier meltwater, finally leading to the sudden drainage in 2019. Before this outburst, a 2-m high moraine dam retained the lake. Continuously inflowing meltwater and the related increasing pressure by the lake water mass eventually broke the moraine dam. Satellite radar interferometry revealed active displacement fringes in the lake basin and moraine dam due to the melting and subsidence of buried ice. An analysis using digital elevation models from 1964 and 2010 also confirms the surface lowering in the lake basin by up to 8.5 m and on the moraine dam by 2 m. Such lowering of the proglacial moraine complex destabilized the moraine dam.

典型光流算法在条纹位移测量中的分辨力和测量范围

典型光流算法在条纹位移测量中的分辨力和测量范围

Toward the quantitative the interpretation of hole-free phase plate images in a transmission electron microscope.

We present progress toward the quantitative interpretation of phase contrast images obtained using a hole-free phase plate (HFPP) in a transmission electron microscope (TEM). We consider a sinusoidal phase grating test object composed of ~5 nm deep groves in a ~13 nm thick amorphous silicon membrane. The periodic grating splits the beam current into direct beam and diffracted side beams in the focal plane of the imaging lens, where the HFPP is located. The physical separation between the beams allows for a detailed study of the HFPP phase shift evolution and its effect on image contrast. The residual phase shift of the electron beam footprint on the phase plate was measured by electron holography and used as input to image simulations that were compared to experimental data. Our results confirm that phase contrast is established by the phase difference between the direct and side beams, which we can estimate by fitting the image contrast evolution in time with an analytical formula describing the image intensity of a sinusoidal strong phase object. We also observed contrast reversal and frequency doubling of the grating image with time, which we interpret as the phase contrast arising from the interference between side beams becoming dominant. Another observation is the lateral displacement of the image fringes, which can be accounted for by a phase difference between the side beams.

Mapping the strain distribution within embedded nanoparticles via geometrical phase analysis

Strain variation within a nanoparticle plays a crucial role in tuning its properties. Geometrical phase analysis (GPA) is typically a powerful tool to investigate the strain in high-resolution transmission electron microscopy (HRTEM) images. It is known that the traditional GPA method measuring the displacement of lattice fringes directly in an HRTEM image is inapplicable to strain measurements on nanoparticles embedded in a matrix, where lattice fringes of nanoparticles are invisible, instead Moiré fringes are present. Furthermore, considering the small size of embedded nanoparticles, generally a few nanometers, no reference region can be chosen and utilized to calculate the relative displacement by GPA. Hence advanced methods need to be developed to break through the barriers of invisible lattice fringes and lack of a reference region. In this work, using α-Fe nanoparticles embedded in sapphire as a test object, we illustrate a GPA method dedicated to embedded nanoparticles. Both the Fourier filter method and the inverse Moiré fringes method were used to reconstruct the invisible lattice fringes of α-Fe nanoparticles. Then a computer-generated image corresponding to an unstrained α-Fe lattice was used as the reference during GPA. The GPA results indicate that there exists a compressive strain in the range of 1.5˜2% within the α-Fe nanoparticles. Our work presents an effective approach to revealing the strain distributions within embedded nanoparticles.

Polarimetric Sensitivity to Torsion in Spun Highly Birefringent Fibers.

We report on experimental studies of polarimetric sensitivity to torsion in spun highly birefringent fibers. Two classes of spun fibers were examined, namely spun side-hole fibers and birefringent microstructured fibers with different birefringence dispersion, spin pitches, and spin directions. The polarimetric sensitivity to torsion was determined by monitoring a displacement of the spectral interference fringes arising in the output signal because of interference of polarization modes and induced by an additional fiber twist. Both the experimental results and the analytical predictions showed that the sensitivity to torsion normalized to the fringe width in the spun highly birefringent fibers increased asymptotically with the twist rate to the value of 1/ π rad−1. We have also studied the polarimetric response to temperature in the spun side-hole fibers. We have found that, in contrast to the torsional sensitivity, the temperature sensitivity decays asymptotically to zero with increasing fiber twist rate. Therefore, the spun fibers with short spin pitches are especially well suited for torsion measurements because the torsional sensitivity and the range of linear response are both enhanced in such fibers, while at the same time, the cross-sensitivity to temperature is reduced.

Experimental and Numerical Investigation of Resonance Characteristics of Novel Pumping Element Driven by Two Piezoelectric Bimorphs

This paper describes the vibration characteristics of a dual-bimorph piezoelectric pumping element under fluid–structure coupling. Unlike the single bimorph used in most previous studies, the proposed device comprises two piezoelectric bimorphs within an acrylic housing. Amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) was used to examine the visible displacement fringes in order to elucidate the anti-phase as well as in-phase motions associated with vibration. Analysis was also conducted using impedance analysis and laser Doppler vibrometer (LDV) based on the measurement of point-wise displacement. The experimental results of resonant frequencies and the corresponding mode shapes are in good agreement with those obtained using finite element analysis. The gain of flow rate obtained by the anti-phase motion of the dual-bimorph pumping element is larger than both those obtained by in-phase motion and the single bimorph pumping element. This work greatly enhances our understanding of the vibration characteristics of piezoelectric pumping elements with two bimorphs, and provides a valuable reference for the further development of bionic pump designs.

Simulating interfering fringe displacements by lateral shifts of a camera for educational purposes

In this manuscript we propose a simple method to emulate fringe displacements in a fringe pattern, due to the interference of two plane waves, by using lateral shifts of a CMOS detector under the scheme of a Twyman–Green interferometric setup, avoiding unwanted vibrations and the need for specific and expensive devices in order to accomplish the task. The simplicity of the proposed experimental setup allows it to be easily replicated and used for teaching or demonstrative purposes, essentially for undergraduate students.

Single-shot real-time three dimensional measurement based on hue-height mapping

A single-shot three-dimensional (3D) measurement based on hue-height mapping is proposed. The color fringe pattern is encoded by three sinusoidal fringes with the same frequency but different shifting phase into red (R), green (G) and blue (B) color channels, respectively. It is found that the hue of the captured color fringe pattern on the reference plane maintains monotonic in one period even it has the color crosstalk. Thus, unlike the traditional color phase shifting technique, the hue information is utilized to decode the color fringe pattern and map to the pixels of the fringe displacement in the proposed method. Because the monotonicity of the hue is limited within one period, displacement unwrapping is proposed to obtain the continuous displacement that is finally used to map to the height distribution. This method directly utilizes the hue under the effect of color crosstalk for mapping the height so that no color calibration is involved. Also, as it requires only single shot deformed color fringe pattern, this method can be applied into the real-time or dynamic 3D measurements.

Dilation of Time Dilation

The study addresses the issue of the so-called time dilation in the sense of the origin of its creation and the physical existence.Based on the work of Lorentz, who the lack of displacement of interference fringes in the Michelson interferometer explained wrongly with, shortening one arm of the interferometer, I propose the construction of the light pulse clock, in which to measure the rate of the passage of time is used constancy speed of light in vacuum.Light clock, the construction of which is described in the paper, stationary in relation to the ether, will measure constant time intervals. The same clock transported, will slow down the pace of his walk as a function of transportation speed v and that is a novelty, will slow depending on its orientation relative to the direction of motion. Light clock transported transversely with respect to the stationary clock will slow gamma times, transported lengthwise will slow gamma to the second power.Basing on the obtained dependences I maintain that time dilation defined in the theory of relativity (SR) as the slowing of the lapse of time, does not physically exist and identification the varying pace of walk clock with the pace of lapse of time I consider a fundamental error resulting from the postulates of this theory.