Theory and verification of moiréfringes for x-ray three-phase grating interferometer

Dual-phase and three-phase grating x-ray interference is a promising new technique for grating-based x-ray differential phase contrast imaging.Dual-phase grating interferometers have been relatively completely studied and discussed.In this paper,the corresponding imaging fringe formula of the three-phase grating interferometer is provided.At the same time,the similarities and differences between the three-phase grating interferometer and the dual-phase grating interferometer are investigated and verified,and that the three-phase grating interferometer can produce large-period moiréfringes without using the analyzing grating is demonstrated experimentally.Finally,a simple method of designing three-phase grating and multi-grating imaging systems from geometric optics based on the thin-lens theory of gratings is presented.These theoretical formulas and experimental results provide optimization tools for designing three-phase grating interferometer systems.

Carrier fringe method of moire interferometry for tiny strain measurements in micro-field

In this paper, we demonstrate a new optical method for tiny strain measurements based on the principle of carrier fringes of moire interferometry. A cross-line grating with frequency of 1200 lp/mm is replicated on the specimen surface, and the strain can be deduced from the changes in carrier fringes before and after the deformation of an object. Four coherent laser beams are used to obtain the carrier fringe patterns of field U and V. Both theoretical analysis and numerical simulation indicate that the ideal accuracy of strain can be controlled within a range of ±1με. Case study of a plane extension experiment shows that the measurement accuracy of strain can be controlled within the range of ±10με. The average strain values of every row of field U and every column of field V can be obtained by using this method, and approximated strain of every pixel in the whole-field can be further acquired, and thus it is possible to measure tiny strains occurred in a micro-field. The technology in this paper can provide comprehensive information for analyzing related mechanical content in the field of MEMS.

SIMULTANEOUS RECORDING OF FRINGE PATTERNS WITH ONE CAMERA

A novel method to separate and simultaneously record the Moiréinterferometry fringe patterns of three deformation fields with only one CCD camera is developed;details of its operation principle,key points and error analysis are presented.With this technique,the deformation in U,V and W fields can be measured simultaneously,so dynamic test with comprehensive information can be performed.The advantage of this technique over other similar techniques lies in its simplicity,easy implementation and low cost.An application of this technique is given to show its feasibility.Technical problems that may be caused with this technique are also analyzed.

Optical/Digital Fringe Multiplication in Projection Moire

In this paper, the optical/digital fringe multiplication (O/DFM) is realized in projection moiré using digital image processing (DIP). Both deformed grating and reference grating are captured using a CCD camera. The reference grating can also be produced using DIP. With the O/DFM, the pattern is multiplied with an image processing software, which is developed using MATLAB 6.5. Also with DIP, the phase shifting can become much simpler, and the automation can be adopted. The multiplied pattern is much thinner and easier to read, and sensitivity of measurement can be enhanced.

AUTOMATIC ORDER-DETERMINATION OF TRANSIENT IN--PLANE DISPLACEMENT MOIRE PATTERNS

This paper presents a fringe-carrier method that eliminates sign ambiguity of transient moire fringes which can be used to automatically determine the relative orders. A fringe carrier is preset in the static state of the specimen and the dynamic in-plane displacements are recorded as the modulation to the frequency of the carrier fringes when the specimen is loaded by impact. According to a modulating criterion developed from the modulation degree, the fringes of the transient moire patterns keep monotonical in orders so that they can be automatically encoded in grey levels by a digital image system. The moire orders purely caused by dynamic loadings are evaluated by subtracting the grey-value of the unmodulated carrier image from that of the modulated carrier images encoded by their orders. With the subtracted moire orders the strain components can be obtained, and, correspondingly, the histograms of dynamic displacement moire images are shown with order variation by image-difference.

Fringe optimization for structured illumination super-resolution microscope with digital micromirror device

Structured illumination microscopy(SIM)is a promising super-resolution technique for imaging subcellular structures and dynamics due to its compatibility with most commonly usedffuorescent labeling methods.Structured illumination can be obtained by either laser interference or projection of fringe patterns.Here,we proposed a fringe projector composed of a compact multiwavelength LEDs module and a digital micromirror device(DMD)which can be directly attached to most commercial invertedffuorescent microscopes and update it into a SIM system.The effects of the period and duty cycle of fringe patterns on the modulation depth of the structured lightfield were studied.With the optimized fringe pattern,1:6×resolution improvement could be obtained with high-end oil objectives.Multicolor imaging and dynamics of subcellular organelles in live cells were also demonstrated.Our method provides a low-cost solution for SIM setup to expand its wide range of applications to most research labs in thefield of life science and medicine.

Moire Patterns of θ'Precipitates in Al-Cu Alloy

A θ＇precipitate in an Al-Cu alloy was imaged.Its Moire patterns shown by TEM were discussed.

STM Study of Moiré Patterns on HOPG

Moiré patterns on HOPG were studied with scanning tunneling microscopy （STM）. The results reveal that the observed Moiré patterns originate from the defects locating several layers below the surface, which presents the first experimental evidence supporting the prediction that in HOPG the nanoscale electronic waves can propagate through several layers without obvious decay.

Melting of electronic/excitonic crystals in 2D semiconductor moirépatterns:A perspective from the Lindemann criterion

Using the Lindemann criterion,we analyzed the quantum and thermal melting of electronic/excitonic crystals recently discovered in two-dimensional(2D)semiconductor moirépatterns.We show that the finite 2D screening of the atomically thin material can suppress(enhance)the inter-site Coulomb(dipolar)interaction strength,thus inhibits(facilitates)the formation of the electronic(excitonic)crystal.Meanwhile,a strong enough moiréconfinement is found to be essential for realizing the crystal phase with a wavelength near 10 nm or shorter.From the calculated Lindemann ratio which quantifies the fluctuation of the site displacement,we estimate that the crystal will melt into a liquid above a critical temperature ranging from several tens Kelvin to above 100 K(depending on the system parameters).

A NEW METHOD FOR CONSTRUCTING DIGITAL-STRAIN-FIELD-IMAGES FROM MOIRE PATTERNS

A new method for constructing digital-strain-field-image from a moire pattern with the help of digital image processing technique is proposed in this paper. The digital-strain-field-image expresses the strain values directly by its grey levels. The digital-strain-field-image can be obtained by making a differentiation for the digital moire pattern and doing a simple division operation. This image not only gives the visual strain field distribution, but also gives the strain values of every point. This method is simple and applicable and has satisfactory accuracy.

基于Talbot-Moiré效应长焦测焦仪的设计及校准技术研究

为了满足100m^3km特长焦距参量的测试校准需求,采用Talbot-Moiré条纹技术法,设计了一套长焦测焦仪.针对影响仪器测量不确定度的系统参量,分别设计了校准方法,并对仪器测量不确定度评定结果进行了实验比对验证.结果表明,校准后仪器测量不确定度评定为6.4%;校准后的长焦测焦仪测量结果与刀口仪测量结果满足测量不确定度比对公式;对比结果最大为0.64,小于1;长焦测焦仪测量不确定度评定合理.该研究验证了长焦测焦仪系统参量校准方法的可行性.

计算机模拟Moire条纹现象

利用计算机图像技术产生周期性条纹方法模拟光栅叠加实现Moire条纹现象.考察Moire条纹的空间放大作用,研究一块光栅相对另一块平移时产生的Moire条纹移动过程,计算Moire条纹在平移过程中探测器的输出变化关系.

用Moire条纹偏转技术测量金属杆的线膨胀系数

推导用 Moire 条纹偏转技术测量金属杆的线膨胀系数的计算公式,并且作了实验。和手册中的数据作了比较,证明了这种方法是可行的,且测量精度也是满意的。

Fourier方法分析Moire条纹

该文用Fourier光学方法分析了分离一定距离的2个Ronchi光栅产生的Moire条纹。在第二块光栅后面直接观察,所得Moire条纹实质上为多光束干涉条纹。在第二块光栅后面加上滤波系统,适当滤波后,Moire条纹成为三光束干涉条纹或双光束干涉条纹。文中对滤波后的Moire条件进行了理论分析,给出了零号频谱滤波和Ⅰ号频谱滤频波下Moire条纹的方程和对比度,得到条纹的方程和对比度与两光栅间距的关系,并给出了与理论相一致的实验结果。

Moiré条纹密度对条纹图噪声及相位混频的影响

分析了Moiré条纹密度对条纹图噪声及相位混频的影响,提出了一种调整Moiré条纹密度的方法以有效减少条纹图噪声与包裹相位图噪声,并消除条纹过密产生的相位混频。试验测量表明,该方法能够获得可靠的测量结果,具有较好的测量精度。

获得高质量Moire条纹信号的一种新方法

在细栅距的幅光栅系统中，衍射效应是很明显的，其能量约占总能量的１０～４０％左右，这种衍射光是造成Ｍｏｉｒｅ光电信号对比度不好和正弦性差的根本原因。本文分析了衍射光栅副±１级Ｍｏｉｒｅ条纹的位相关系与光栅副间隙等因素的关系，提出了利用±１级Ｍｏｉｒｅ条纹来获得高质量Ｍｏｉｒｅ条纹信号，实际应用，效果良好。

Separation of contact stress components by moire interferometry

A hybrid technique of combining moire measurement and analytical solution is developed to separate the normal and the tangential components of distributed contact stresses between two co-plane bodies. The moire interfe-rometry offers the displacement fields near the deformed contact zone, from which the tangential strains and boundary slopes of the deformed configurations can be evaluated. Those experimental results provide boundary conditions for the discrete integration of Flamant＇s solutions, to inversely compute the separated components of the contact stresses.

Review of phonons in moiré superlattices

Moirépatterns in physics are interference fringes produced when a periodic template is stacked on another similar one with different displacement and twist angles.The phonon in two-dimensional(2D)material affected by moirépatterns in the lattice shows various novel physical phenomena,such as frequency shift,different linewidth,and mediation to the superconductivity.This review gives a brief overview of phonons in 2D moirésuperlattice.First,we introduce the theory of the moiréphonon modes based on a continuum approach using the elastic theory and discuss the effect of the moirépattern on phonons in 2D materials such as graphene and MoS_(2).Then,we discuss the electron-phonon coupling(EPC)modulated by moirépatterns,which can be detected by the spectroscopy methods.Furthermore,the phonon-mediated unconventional superconductivity in 2D moirésuperlattice is introduced.The theory of phonon-mediated superconductivity in moirésuperlattice sets up a general framework,which promises to predict the response of superconductivity to various perturbations,such as disorder,magnetic field,and electric displacement field.

相界面的Moiré条纹研究

运用高分辨透射电子显微镜对取向关系分别为45°[100]和66°[011]的MgO/Cu界面结构进行了研究,界面附近由于MgO与Cu相互重叠而出现Moiré条纹,两种不同取向关系所对应的Moiré条纹分别为平行和旋转条纹,对两种Moiré条纹的取向及间距进行了分析,理论分析与实验结果符合得很好.

OPTICAL PROPERTIES OF 2D MATERIALS Signatures of moire excitons

In van der Waals heterostructures of atomically thin 2D materials, the inevitable lattice mismatch and twisting between the building blocks always lead to the formation of Moire pattern, which is a periodic spatial pattern of varying atomic registries. Theory has predicted that such a nanoscale moire landscape can endow excitons highly intriguing properties (Science Advances 3, e1701696 (2017)), including their confinement in an array of quantum dot like potential traps with circularly polarized valley optical selection rules.