Improved algorithm for image encryption based on stochastic geometric moiré and its application

A technique based on optical operations on moiré patterns for image encryption and decryption is developed. In this method, an image is encrypted by a stochastic geometric moiré pattern deformed according to the image reflectance map. The decryption is performed using pixel correlation algorithm in the encrypted image and the stochastic geometrical moiré pattern. The proposed technique has a number of advantages over existing encryption techniques based on moiré gratings. No original moiré grating can be reconstructed only from the encrypted image. Stochastic moiré grating can be deformed in any direction what is an important factor of encryption security. Finally, the quality of the decrypted image is much better compared to decryption methods based on the superposition of the regular and deformed moiré gratings. The proposed technique has a great potential, because the process is performed using computational algorithms based on optical operations and optical components are avoided.     

Formulation of moiré fringes based on spatial averaging

The use of moiré technique in measurements often involves locating the position of moiré fringe and in some cases determining its profile. Due to intensity fluctuation in the fringe pattern, these measurements are accompanied by some errors. It is possible to define a smoothed version of the original fringe pattern and then formulate the related subject in accordance with the characteristics of this new pattern. This procedure reduces these types of errors and gives a well-defined profile of the fringes. In this paper a formulation of moiré phenomenon based on spatial averaging is presented which, without ignoring any of frequencies, leads to a smooth profile.     

TDI imaging and scanning moiré for online defect detection

This paper explains the application of scanning moiré in association with TDI (Time Delay and Integration) imaging for complete peripheral inspection of cylindrical objects. Based on the structured light technique, a grating pattern modulated by deformations, such as dents on the surface of a rotating cylindrical object, is recorded using a TDI camera. The illumination system consists of an intensity modulated, line generating laser diode aligned at an angle to the camera axis. By using the TDI option for recording every nth line, an online scanning moiré pattern is generated. After providing a simple explanation of the scanning moiré, the effects of object rotation speed and TDI scan speed on the fringe pattern are discussed and demonstrated. The techniques presented here offer low cost solutions to industrial machine vision tasks related to peripheral imaging and inspection of cylindrical objects.     

STEM (scanning transmission electron microscopy) analysis of femtosecond laser pulse induced damage to bulk silicon

This work reports on the structural changes that take place in wafer grade silicon when it is micro-machined with ultra-short laser pulses of 150 fs duration. A Chirped Pulse Amplification (CPA) Ti:Sapphire laser was used, with an operating wavelength centered on 775 nm and a maximum repetition rate of 1 KHz. The laser induced damage was characterized over the fluence range 0.43–14 Jcm^-2, and for each fluence a progressively increasing number of pulses was used. The analytical tools used to characterize the samples were all based upon electron microscopy. A 30 KeV scanning transmission electron microscope (STEM) imaging technique was developed to observe defects in the crystal lattice and the thermal-mechanical damage in the area surrounding the laser machined region. Mechanical cross sectioning (in conjunction with Scanning Electron Microscope (SEM) surface imaging) was also used to reveal the internal structure, composition, and dimensions of the laser machined structures. Based on this analysis, it will be shown that laser machining of silicon with femtosecond pulses can produce features with minimal thermal damage, although lattice damage created by mechanical stresses and the deposition of ablated material both limit the extent to which this can be achieved, particularly with high aspect ratios. A key feature of the work presented here is the high-resolution STEM images of the laser-machined structures. PACS  42.65.Re; 42.62.Cf; 61.80.Ba; 61.82.Fk; 68.37.Hk; 68.37.Lp     

Measurement of vibration amplitude by an optical fiber-based moiré interferometer

A projected-fringe fiber-based moiré interferometer is proposed to measure the local amplitude vibration of a diffuse surface. The technique is based on an optical fiber interferometer which projects interference fringes on the object surface. The visibility of these carrier fringes is modulated by a function of local amplitude vibration. Full-field quantitative analysis is performed by analyzing the fringe pattern with a 2-D Fourier transform method. Theoretical details, and experimental results are presented.     

Image hiding based on time-averaging moiré

Image hiding based on optical time-averaging moiré technique is presented in this paper. It is a new visual decoding scheme when the secret image is embedded into a moiré grating and can be interpreted by a naked eye only when the image is harmonically oscillated in a predefined direction. The secret image is visualized at strictly defined amplitude of oscillation. Computational and experimental examples are used to demonstrate the functionality of the method.     

Measurement of the thermal expansion coefficients of ferroelectric crystals by a moiré interferometer

A moiré interferometer is used to measure the thermal expansion of two ferroelectric crystals, LiNbO₃ and KTiOPO₄. The crystal samples are patterned with a chromium reflective grating and used as a diffractive component in a reflective grating interferometer. The thermal expansion of all the three axes of congruent LiNbO₃ and of x and y axes of the flux-grown KTiOPO₄ were measured from room temperature to 200 °C. For this temperature range the thermal expansion coefficient has been modeled by a second-order polynomial and its coefficients have been estimated by accurate analysis of the resulting moiré fringe pattern.     

On a Comparison between Mechanical Stress Isolines and X-Ray Interferometric Moiré Curves

In the present paper, it is demonstrated that mechanical stress isolines and x-ray interferometric moiré curves are identical. In particular, if dislocations are incorporated into the crystal block of an interferometer, the moiré pattern will coincide with dislocation stress isolines calculated in the context of linear elasticity theory.     

相移阴影莫尔基于迭代LSM拟合

相移阴影莫尔技术相位高度存在着非线性关系,无法在全场获得均匀相移,因而致使经典的相移算法不能得到精确解.对此,提出了一种基于最小方差迭代的相移阴影莫尔技术,该技术通过垂直光栅面等间距移动光栅来产生相移,但光栅移动距离可不采用固定值,所以相移过程灵活|使用在高度解调过程中确定的逐点相移增量来抽取精确的测量相位,实现了相移阴影莫尔技术中固有的相位高度非线性误差补偿.结果表明,该方法可通过干涉图计算光栅的移动量,具有相移器的自标定特性.     

Femtosecond laser pulse irradiation of Sb-rich AgInSbTe films: Scanning electron microscopy and atomic force microscopy investigations

The single-layer and multilayer Sb-rich AgInSbTe films were irradiated by a single femtosecond laser pulse with the duration of 120 fs. The morphological feature resulting from the laser irradiation have been investigated by scanning electron microscopy and atom force microscopy. For the single-layer film, the center of the irradiated spot is a dark depression and the border is a bright protrusion; however, for the multilayer film, the center morphology changes from a depression to a protrusion as the energy increases. The crystallization threshold fluence of the single-layer and the multilayer films is 46.36 mJ/cm², 63.74 mJ/cm², respectively. PACS 79.20.Ds; 78.55.Qr; 78.66.Jg; 68.37.Ef; 68.37.Ps     

Recent advances in spin-polarized scanning tunneling microscopy

Considerable progress in the field of spin-polarized scanning tunneling microscopy (SP-STM) has been achieved recently by gaining a high degree of control with regard to properties of the tunneling tip. It is found that by choosing the appropriate material for the magnetic thin film coating of the tip sensitivity to either the samples in-plane or perpendicular magnetization component can be achieved. Using SP-STM in external magnetic fields, domains and domain walls of two atomic layers thick Fe on a W(110) substrate are studied. A residual domain of enhanced stability against remagnetization is observed. Furthermore, a new imaging mechanism is identified which allows the use of even non-magnetic tungsten tips to observe contrast between magnetic domains and domain walls. The effect exploited is a modification of the electronic band structure which is induced by spin–orbit coupling. PACS 75.50.Ak; 75.75.+a; 68.37.Ef     

Lattice bending in x-ray interferometers

This paper investigates both theoretically and experimentally the effect of lattice bending on the output signals of a two-crystal x-ray interferometer of the Laue LLL type. The cross section intensity of the outgoing beams is modulated by the moiré effect produced by the overlapping of the analysing lattice on the x-ray standing field in front of it. Since the intensities of the transmitted and diffracted beams are integrated, the moiré pattern causes loss of visibility in the x-ray fringes and a non-linear phase shift, which depends on the pitch alignment of the analysing crystal with respect to the fixed crystal. The analysis of this phase shift allows the lattice curvature to be estimated.     

Imaging photothermal microscopy for absorption measurements of optical coatings

For absorption measurement of large-aperture optical coatings, a novel method of imaging photothermal microscopy based on image lock-in technique is presented. Detailed theoretical analysis and numerical calculation are made based on the image photothermal technique. The feasibility of this imaging method is proved through the coincidence between the theoretical results of single spot method and multi-channel method. The measuring speed of this imaging method can be increased hundreds of times compared with that of the raster scanning. This technique can expand the applications of photothermal technique.     

Investigation of the mechanism of polarization switching in ferroelectric capacitors by three- dimensional piezoresponse force microscopy

A mechanism for the switching behavior of (111)-oriented Pb(Zr,Ti)O₃-based 1×1.5 m² capacitors has been investigated using three-dimensional piezoresponse force microscopy (3D-PFM). A combination of vertical and lateral piezoresponse force microscopy (VPFM and LPFM) has been used to map the out-of-plane and the in-plane components of the polarization. The three-dimensional polarization distribution was reconstructed by quantitative analysis of the PFM amplitude images of poled PZT capacitors while taking into account contrast variations in the PFM phase images. The switching behavior of the capacitors was determined by comparison of the static domain patterns in the same capacitors after both positive and negative poling. While 180° degree switching was observed, surprisingly, the switching process was dominated by 90° polarization vector rotation. Furthermore, central regions of the capacitors were characterized by the presence of charged domain boundaries, which could lead to imprint (preference of one polarization state over another). PACS 85.50.Gk; 77.80.Fm; 77.80.Dj; 68.37.Ps     

The interpretation of x-ray interferometer moiré patterns

In most experiments the x-ray-interferometer moire bands take the form of curves which complicate the problem of reconstructing the distribution pattern of deformations in single-crystal blocks giving rise to such moirés. In the paper we consider the regularities in the variation of the interplane distances and relative rotations of these planes for which moiré lines close in form to the experimental ones are obtained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 8–12, April, 1984.     

Moiré properties of Walsh functions

A new type of moiré experiment is presented. Each grating is synthesized by Walsh functions. These functions have the property of being cyclically periodic, and the resulting moiré is also cyclically periodic. Gratings synthesized by different Walsh functions were employed and a contouring measurement is described.     

Structural and ferroelectric properties of Pb1-xSrxTiO3 thin films

Strontium-modified lead titanate (PST) thin films with composition Pb_1-xSr_xTiO₃ (0.10<x0.60) were grown on Pt/Ti/SiO₂/Si substrates using a soft chemical process. The crystallization of the PST thin films was achieved by heat treatment at 600 °C. The structural and microstructural modifications in the films were studied using X-ray diffraction (XRD) and atomic force microscopy, respectively. The XRD study shows that the lattice parameters of polycrystalline PST thin films calculated from X-ray data indicate a decrease in lattice tetragonality with the increase in strontium content in these films. This indicates a gradual change from tetragonal to cubic structure. By atomic force microscopy analysis, the average grain size of the thin films was systematically reduced with the increase in Sr content. The dielectric property of the thin films was found to be strongly dependent on the Sr concentration. With 60 at.% Sr content, a ferroelectric to paraelectric phase transition was observed at room temperature. PACS 61.10.Nz; 68.37.Ps; 77.55.+f; 77.84.-s; 81.15.-z     

Graphitization of carbon nanofibers: visualizing the structural evolution on the nanometer and atomic scales by scanning tunneling microscopy

The structural evolution of carbon nanofibers submitted to high-temperature (1800, 2300, and 2800 °C) heat treatments has been investigated at the nanometric and atomic scales by means of scanning tunneling microscopy (STM). To complement the local STM observations, X-ray diffraction and Raman spectroscopy characterization of the samples were also carried out. On the nanometer scale, the as-grown nanofibers displayed an isotropic platelet morphology that developed into striped arrangements of increasing width at 1800 and 2300 °C, and into large, atomically flat terraces at 2800 °C. On the atomic scale, the starting nanofibers were characterized by tiny (2 nm) crystallites. The crystallites were observed to coalesce at 1800 °C into appreciably larger (3–4 nm) although still defective units. Atomic structures evidencing truly graphitic ordering (i.e. the typical STM triangular pattern with a periodicity of 0.25 nm) started to develop at 2300 °C. At this temperature, a segregation of graphitic domains and highly defective areas was noticed and attributed mainly to the mobility and subsequent aggregation of point defects (atomic vacancies). Long-range atomic-scale order was generally established in the nanofibers heat treated at 2800 °C, where only some incompletely graphitized, fragmentary graphenes were left on the surface. PACS 81.07.-b; 81.40.Ef; 68.37.Ef     

Photorefractive Fourier transform profilometer for the measurement of 3-D object shapes

In the present work dynamic moiré-like fringe patterns, produced by photorefraction with low spatial frequencies, applied for profile determination of small objects is proposed. Basically, a Fourier transform profilometry technique is developed for an automated profile determination. This means, as far as we know, a new experimental procedure that exploits the real time holographic two wave mixing in Bi₁₂TiO₂₀ crystal sample. Besides, the mainly advantages of this procedure are, comparatively to the classical fringe projection method using the Michelson interferometer, best fringe pattern contrast, less speckle noise, absence of noises produced by spurious reflections and, the most significant, a pure sinusoidal shape obtained by dynamic holographic moiré-like process using photorefraction.     

A study on the 3-D measurement by using digital projection moiré method

Moiré topography method is a well-known non-contacting 3-D measurement method. Recently, the automatic 3-D measurement technique by moiré topography has been developed in order to apply to the engineering and medical fields. The projection moiré topography is very attractive because of its high measuring speed and high sensitivity. In this paper, using the two-wavelength methods of projection moiré topography was investigated to measure the 3-D shape of an object with 2π-ambiguity problems. Rapid measurement can be accomplished by the synchronization between CCD camera and projector. The experimental results prove that the proposed scheme is capable of finding absolute fringe orders, so that the 2π-ambiguity problems can be effectively overcome so as to treat large step discontinuities in measured objects.