Moire Fringes Research Articles

Experimental implementation of visual cryptography based on time average moiré

Geometric moire is a classical in-plane whole-field non-destructive optical experimental technique based on analysis of visual patterns produced by superposition of two regular gratings that geometrically interfere. Two basic goals exist in moire pattern research. The first is the analysis of moire patterns. The task is to analyze and characterize the distribution of moire fringes in a moire pattern. Most of the research in moire pattern analysis deals with the interpretation of experimentally produced patterns of fringes and determination of displacements (or strains) at centerlines of appropriate moire fringes. Another goal is moire pattern synthesis when the generation of a certain predefined moire pattern is required. The synthesis process involves production of such two images that the required moire pattern emerges when those images are superimposed. Moire synthesis and analysis are tightly linked and understanding one task gives insight into the other.

CCD在自准直仪中用于莫尔条纹成像研究

The measuring principle of the grating autocollimator is discussed based on vertical stripes Moire detection.Using the Fourier optics theory,it is able to deduce that the method is feasible which uses the linear array CCD to replace the instructions grating to produce moire fringes in the autocollimator.The experiment validates that when the ratio s between projection grating constant d2 on CCD and grating constant d1 equals to 1.01,the amplification ratio of the vertical moire fringes can reach to 14.14.The proposed method can solve the problem that the grating diffraction affects the trial result,simplify the autocollimator optical system,and enhance the system′s resolution.

基于Talbot-Moiré法测量透镜焦距的莫尔条纹的图像处理

Based on Talbot effect and Moire fringes of Ronchi gratings,focal length measurement of the long focal length is carried out. The focal length of measured lens can be figured out accurately according to its relation to the slope coefficient of Moire fringes. To get the slope of Moire fringes, the image of Moire fringes is mainly filtered or smoothed by mathematics morphological method to enhance the contrast of fringes effectively. Then the filtered image is processed by thinning to single pixel width. The fringes are labeled to fitting lines to calculate the slope coefficient accurately,and the error of focal length is 0.10%.

X-ray phase imaging of a packaged IC chip using X-ray array source

We have developed a novel configuration of an X-ray grating interferometer for the phase imaging of a packaged IC chip. A square source grating is used, and a beam splitter and an analyzer grating are positioned downstream of the investigated sample. In the proposed method, the period of source grating is smaller than the last of two gratings, the configuration of which could be implemented for phase imaging. Phase images retrieved using the principle of in-line phase contrast imaging and phase detection are the phase stepping method used in the X-ray grating interferometer. The wrapped phase images of the packaged IC chip are obtained from nine Moire fringe patterns, using an exposure time of 34ms for each scan.

Fabrication Process for Large Size Mold and Alignment Method for Nanoimprint System

Nanoimprint technology is considered one of the mass production methods of the display for cellular phone or notebook computer, with Anti-Reflection Structures (ARS) pattern and so on. In this case, the large size mold with nanometer order pattern is very important. Then, we describe the fabrication process for large size mold, and the alignment method for UV nanoimprint system. We developed the original mold fabrication process using nanoimprint method and etching techniques. In 66 × 45 mm2 area, 200nm period seamless patterns were formed using this process. And, we constructed original alignment system that consists of the CCD-camera system, X-Y-θ table, method of moire fringe, and image processing system, because the accuracy of pattern connection depends on the alignment method. This alignment system accuracy was within 20nm.

Deflection Measurement and Determination of Young’s Modulus of Micro-cantilever Using Phase-shift Shadow Moiré Method

The deflection of micro-structures have been previously measured using optical interferometry methods. In this study, the classical phase-shift shadow moire method (PSSM) was applied to measure the deflection of a silicon micro-cantilever and to determine the Young’s modulus of the cantilever material. The modulus value was determined from the profile based on deflection equation. A normal white light source and a grating of 40 line pairs per mm were used to generate the moire fringes. Since the use of white light and high-resolution grating produces low contrast moire fringes, the fringe visibility was enhanced by applying contrast enhancement and filtering techniques. The Young’s modulus of the silicon cantilever material was estimated to be 165.9 GPa with an uncertainty of ±11.3 GPa (6.8%). The experimental results show that the PSSM method can be successfully applied for characterizing micro-cantilevers. Comparison of the deflection profile from the proposed method and a commercial 3-D optical profiler showed that the measurement range and sensitivity of PSSM are not affected by the poor contrast images.

Shrinkage Measurement in Concrete Materials using Cure Reference Method

This paper describes the details of using Cure Reference Method (CRM) to determine the shrinkage that develops in concrete materials. The technique involves the replication of diffraction grating on the concrete specimen during curing. After demolded, the specimen is stored in a chamber where a specific drying condition is maintained for 6 days. Every day in this period, the specimen is removed from the chamber and a set of the consecutive moire fringe patterns are recorded with the help of a specially-designed stage. An automated fringe analysis program is developed to obtain the full-field displacement and strain information. Shrinkage as a function of location, time, and drying conditions is measured. A numerical method is developed in order to obtain material properties from the complex geometry used in the tests. The test in different drying condition and the ring test are performed, and their results are compared with FEA to validate the constructed model.

One-Pot Room-Temperature Synthesis of Single-Crystalline Gold Nanocorolla in Water

A room-temperature nanocarving strategy is developed for the fabrication of complex gold nanoplates having corolla- and propeller-like architectures. It is based on the simultaneous growth and etching of gold nanoplates in aqueous solution, which occur in the course of photoreduction of Au(OH)(4)(-) ions. The presence of bromide ion, poly(vinylpyrrolidone) (PVP), and molecular oxygen is indispensable, where bromide ions play multiple roles. First, they promote formation of nanoplate structures by forming adlayers on the fcc(111) surface. Second, they facilitate oxidative dissolution of gold nanocrystals by converting the oxidized Au(I) species to soluble AuBr(2)(-) ions, which lead to the formation of ultrathin nanocrevasses. PVP also stabilizes the nucleation of gold nanoplates. Although the overall reactions proceed in one-pot, the crystal growth and etching show interplay and occur with different kinetics due to changes in the concentration of Au(OH)(4)(-) and other species with time. Corolla- or propeller-like gold nanoplates formed under these conditions are single-crystalline, as indicated by selected area electron diffraction patterns and the observation of moire fringes. The morphology of corolla- or propeller-like gold nanoplates is controllable depending on the concentration of bromide ion and PVP in the aqueous mixture. On the basis of these results, a preliminary mechanism is proposed which involves the concurrent crystal growth and oxidative etching on the surface of nanocrystals.

Specific features of the epitaxial growth of narrow-gap InSb quantum dots on an InAs substrate

Arrays of coherent InSb quantum dots (QDs) have been fabricated by liquid-phase epitaxy on InAs substrates in the temperature range T = 420–450°C. The QDs with a density of (0.9−2) × 1010 cm−2 were 3 nm high and 13 nm in diameter. A bimodal QD size distribution was observed, which was accounted for by a combined growth mechanism of these nanoobjects. Structural characteristics of a separate InSb QD formed on the InAs surface were studied for the first time by atomic-force and transmission electron microscopies. Moire fringes were observed for the first time for QDs in the InSb/InAs system, with the moire period of 3.5 nm corresponding to InSb QDs without an admixture of arsenic.

Evaluation of the curvature of an object by Talbot interferometry

In this study a modified method of Talbot interferometry is developed to evaluate the curvature of an object. The tilt angle of moire fringe formed by two gratings is related to the wavelength, the grating periods, the angle between these two gratings, and the object curvature. Therefore, substituting the known experimental parameters into a special derived equation the object curvature can be evaluated. In order to show the validity of this method, stainless steel balls with curvatures of 1.326 and 1.261 mm−1 were measured. The measurement resolution of curvature was about 3.729 × 10−3 mm−1. It is shown that this method is suitable for both transmission and opaque objects with high accuracy.

Characterization of interphase-precipitated nanometer-sized carbides in a Ti–Mo-bearing steel

The aim of this work was to investigate the interphase-precipitated nanometer-sized carbides in a Ti–Mo-bearing steel that formed during the isothermal transformation at a temperature in the ferrite/austenite phase field. Through the analyses of selection area electron diffraction patterns, moire fringes in high-resolution transmission electron microscopic lattice images and high-angle annular dark-field scanning transmission electron microscopy, these ultra-fine, banded dispersive carbides have been identified as MC carbides with the NaCl-type crystal structure that contains high levels of Ti and Mo.

RESEARCH ON THE MOIRE CHROMATOGRAPHY TECHNIQUE AND ITS APPLICATION

This paper explains the Moire chromatography technique and the optical characteristics when the light crosses the 3D air flow field. Based on this, taking grating, CCD camera, optical filter and diaphragm as the main device, a multi-direction Moire chromatography optical system was designed. The system consists of five detective light paths, in each detective light path there is parallel and same periodic grating and filtering minipore placed on the lens' focal length plane; the grating is used to adjust the space length and angle between the two gratings, and the filtering minipore is used to remove the unorderly high frequency intermix in the Moire fringe. Utilizing the computer escalator method to convert the tested value, the vivid interference fringe of tested parameter can be obtained. The application of this system in precision measurement and medicine is also analyzed and discussed.

Microstructure characterization of hot-pressed β-silicon nitride containing β-Si 3N 4 seeds

Self-reinforced silicon nitride ceramics were synthesized by introducing 5 wt% previously prepared β-Si 3N 4 seeds into a mixture of α-Si 3N 4 and 8 wt.% of sintering additive. The microscopic evidence indicates that β-Si 3N 4 seeds play an important role in microstructural development and mechanical properties for silicon nitride ceramics. The growth of β-Si 3N 4 grains is initiated from the seeds, resulting in a core/shell microstructure observed in the abnormal grain growth. The internal dislocation, π-boundary, and Moire fringes are present in Si 3N 4 grains, which were formed to compensate the mismatch and compositional differences between the two grains. Coalescence can occur at the final stage of sintering.

Solid-state dye laser with moiré gratings

We fabricated distributed-feedback (DFB) solid-state dye lasers with moire gratings. We formed a moire grating pattern by superimposing two grating patterns with a rotation angle. The moire gratings were fabricated by an “etchless” process utilizing a two-beam interference method. The gratings were coated with solidified rhodamine-B. The five laser devices were pumped with the second harmonic generation of a Nd:YAG laser and we obtained narrow-banded laser oscillations at 590, 600, 610, 620, and 630 nm wavelength. Full widths at half maximum of laser spectra were less than 0.5 nm. The results indicated that a moire fringe can function as a resonator of DFB solid-state dye lasers.

As cluster array formation in GaAs grown by molecular-beam epitaxy at a low temperature and δ-doped with phosphorus

GaAs films δ-doped with phosphorus (one monolayer) were grown by molecular beam epitaxy at a temperature of 200°C (LT-GaAs), isochronally annealed at 400, 500 or 600°C, and studied by transmission electron microscopy. Analysis of the moire fringes in the electron microscopy images of the clusters formed upon annealing revealed that their microstructure and orientation relationship correspond to the parameters of pure As clusters in GaAs; hence, there is no considerable incorporation of phosphorus from the matrix into the forming clusters during precipitation of excess As. Examination of the cluster’s spatial distribution across the LT-GaAs films showed no variation in the cluster array’s concentration near the P °-layers for the used growth and annealing conditions. Thus, phosphorus, being introduced into a LT-GaAs film in the form of °-layers, behaves as the isovalent Al impurity and differs from such isovalent impurities as In and Sb by the effect on the spatial distribution of As clusters.

1A1-C17 モアレ縞を用いた加速度可視化マーカ

We developed an acceleration visualization marker using moire fringe which can display a stripes pattern that corre spond to a magnitude of acceleration. The proposed marker consists of two elastic plates and two plates printed with strips and needs not electric elements such as an amplifier and strain gauges. When proposed marker takes a picture by using a high-speed camera, an acceleration can be measured from remote place. We have experimentally verified the utility of the proposed marker by taking a picture with the camera, and processing the image.

Alignment measurement method for imprint lithography using moiré fringe pattern

A simple and high-accuracy alignment measurement method based on a moire fringe pattern is proposed. It involves relative rotation positioning and relative linear displacement measurement. Taking full advantage of the magnification effect of moire fringe in angular and linear displacement, the relative rotation between the template and the wafer is determined first by measuring the inclination of the moire fringe, and then the relative linear displacement between them is acquired by evaluating the spatial phase shift of two matched moire fringes. The frequency components in the orthogonal directions of the fringe image obtained by a fast Fourier transform (FFT) and zooming process are used to measure the inclination of the moire fringe. By selecting different orthogonal directions, a moire fringe with any inclination can be measured accurately. When gratings are adjusted to parallel, a frequency-domain analysis is also used to extract the spatial phase of fringes at a given frequency. According to the relationship between spatial phase and linear displacement, the misalignment is detected. In experiments, the repeatability for the misalignment measurement has reached 4.8 nm (3).

Time-averaged patterns produced by stochastic moiré gratings

A simple computational algorithm is proposed for visualization of time-averaged moire fringes. Time-averaging numerical techniques can be exploited for the construction of a cryptographic hash function. It appears that visualization of values of that hash function at continuously increasing amplitude of harmonic oscillation can produce interesting optical patterns. Chaotic and visually intriguing patterns are observed when the input of the hash function is selected as an array of random numbers uniformly distributed in the interval [0;1]. Such stochastic moire gratings produce aesthetically beautiful pictures and can be used to explore aspects of the quality of a random number generator.

반복사인격자에서 동시에 생기는 두 가지 무아레 무늬를 이용한 회전변위의 가시적 측정

컴퓨터 전산모의와 회전자를 이용한 실험을 통하여 회전변위에 따른 반복사인격자 한 쌍이 만드는 무아레 무늬의 변화를 세밀하게 조사하여 반복사인격자가 겹쳐서 동시에 생기는 두 가지의 서로 다른 무아레 무늬를 사용하는 작은 회전변위를 측정하는 가시적 방법을 보여준다. 이 무아레 무늬는12도 이상의 큰 각도 측정에 유용한 장주기의 넓고 긴 직선무늬와 12도 이하의 작은 각도 측정에 유리한 좁고 짧은 복잡한 직선무늬로 이루어져 있다. 그리고 무아레 무늬의 회전방향에 따라 회전변위의 회전방향도 동시에 가시적으로 판별할 수 있다. We present the precise visual measurement method of rotational displacements using two different moire fringes simultaneously generated by repeated sinusoidal gratings. We investigate the variation of moire fringes depending on rotational displacements through computer simulation and experiment using a rotator in detail. The moire fringes are composed of the wide linear fringe part with a long period and the narrow linear fringe part with a short period. These parts are superior to the angle detection of more than 12 degrees and less than 12 degree, respectively. Additionally, the method can be visually used in the determination of the rotational direction by observing the moire fringe's direction.

Characteristic analysis of evanescent wave moiré fringes

Based on the characteristics of evanescent wave moire fringes generated from subwavelength gratings, we numerically investigated the contrast of moire fringes for two gratings with and without a silver slab. The effect of the gratings' geometrical parameters on the contrast of moire fringes is analyzed in detail by using the finite-difference time domain method. Numerical results show that great enhancement of the contrast of evanescent wave moire fringes could be achieved by surface plasmon excitations on a silver slab. These evanescent wave moire fringes with high contrast will have potential applications in the nanofabrication field. (C) 2008 Optical Society of America.