Isochromatic fringes in photoelasticity

The structure of the isochromatic fringe pattern in a two-dimensional photoelastic model is investigated with the phase diagram method of the theory of dynamic systems. Isochromatics are interpreted as phase paths (or level curves) of a Hamiltonian system. Possible singularities of the fringe pattern are analyzed.     

Effect of pharmacological suppression of secondary hyperparathyroidism on cardiovascular hemodynamics in predialysis CKD patients: A preliminary observation

Cardiovascular events are the principal cause of mortality in patients with chronic kidney disease (CKD). Secondary hyperparathyroidism (SHPT), a common complication of CKD, contributes to cardiac dysfunction. This study is an attempt to demonstrate the effects of parathyroid hormone suppression with oral calcitriol on cardiovascular hemodynamics. Twenty predialysis CKD patients with SHPT were given calcitriol therapy for 12 weeks. Ten similar patients received placebo. Echocardiographic assessment of cardiac function was performed at baseline and after 12 weeks of treatment. Calcitriol therapy effectively suppressed SHPT. Baseline left ventricular (LV) end diastolic diameter and LV end systolic diameter were 4.86+/-0.48 and 2.86+/-0.33 cm, and the mean FS was 41.02+/-4.79%. Left ventricular end systolic and end diastolic volumes were normal (42.30+/-9.07 and 91.40+/-19.68 mL). The ejection fraction was slightly reduced (53.54+/-3.57%). Pretreatment Doppler indices including E velocity (0.816+/-0.087 m/s), A velocity (0.696+/-0.089 m/s), and E/A ratio (1.193+/-0.210) were significantly impaired. After 12 weeks of calcitriol therapy, there was no significant change in the LV dimensions or ejection fraction, but there was a significant improvement in the diastolic parameters, namely the A velocity (0.680+/-0.084) and E/A ratio (1.238+/-0.180). Secondary hyperparathyroidism is an important factor in the pathogenesis of cardiovascular complications in CKD. There is evidence to support that correction of hyperparathyroidism can improve the systolic dysfunction seen in advanced kidney disease. This study shows that diastolic dysfunction seen in predialysis CKD patients may also be possibly improved with calcitriol therapy.     

毛玻璃转速对干涉条纹成像质量的影响

针对大平面菲索干涉图像的相干噪声问题,采用旋转毛玻璃片的方法改变光束的相干性,来降低干涉系统的噪声。通过对毛玻璃的转速与条纹对比度和系统信噪比之间的关系进行仿真,获得最佳干涉条纹状态所需要的毛玻璃控制参数。在不同控制参数下获取干涉图像,并分别对各图像的条纹对比度和系统信噪比进行分析。研究结果表明,增加的毛玻璃转速,虽然在一定程度上降低了干涉图像的对比度,但却有效地提高了信噪比,便于后续的干涉图像处理。

     

Generation of carrier fringes in holography and shearography

Double-exposure holography and double-exposure shearography are often used together with the carrier fringe technique, which requires additional shifting of the light source in a prescribed manner between exposures. In the holographic carrier fringe technique, difficulty in prescribing a suitable movement of the light source may be alleviated through visualization of the moiré fringes that are reconstructed by slight displacement of two overlaid families of ellipsoids in a holodiagram. Because shearography is the first differential of holography, it is often impractical to perform two successive optical differentiations on the ellipsoids to visualize the shearographic carrier fringes. A simple method of discerning holographic and shearographic carrier fringes is described. The method is based on the hyperboloids in a holodiagram that represent Young's (interference) fringes produced by the interference of two point sources. The hyperboloids are analogous to holographic carrier fringes, whereas the moiré patterns reconstructed from two overlaid hyperboloids are analogous to shearographic carrier fringes. Use of this method for explaining the formation of deformation fringes in plate bending, as well as the effect of light-source movement on the deformation fringes, is also illustrated.     

Resolving quadrature fringes in real time

In many interferometers, two fringe signals can be generated in quadrature. The relative phase of the two fringe signals depends on whether the optical path length is increasing or decreasing. A system is developed in which two quadrature fringe signals are digitized and analyzed in real time with a digital signal processor to yield a linear, high-resolution, wide-dynamic-range displacement transducer. The resolution in a simple Michelson interferometer with inexpensive components is 5 x 10(-13) m Hz(-1/2) at 2 Hz.     

Black-and-white fringes and the colors of caustics

Fine-scale interference fringes that decorate caustics produced with white light appear black and white with high contrast. This is surprising, as the elementary expectation, supported by theory and computer simulation, is that the fringes should be highly colored. The fringe separation is several arc minutes and therefore close to the resolution limit of the eye. Under magnification (even of a photograph), the colors are revealed. Therefore black-and-white fringes are an illusion, giving a dramatic naked-eye illustration of the fact that the angular resolution of the visual system is better for luminance than for color.     

Photoelectric recording of interference fringes

Summary The comparison of the results of measurements of Fabry and Perot master gages obtained by the photoelectric recording and by taking photographs of interference rings was carried out for a 100-mm-long master gage and for 47-, 80-, and 100-mm long quartz gages. In each case the result coincided with the difference remaining within measurement errors.Advantages of the photoelectric recording method include: its objectivity, reliability, and the speed with which the result is obtained. In addition, the use of this method offers wide possibilities for using in the interference length-measurements of spectral lines from the part of the spectrum close to the infra-red region, which makes possible the extension of the range in which absolute measurements of gage blocks in wavelengths of light can be performed.     

Automatic analysis of speckle photography fringes

Speckle interferometry is a technique adequate to metrological problems such as the measurement of object deformation. An automatic system of analysis of such measurements is given; it consists of a motorized x-y plate positioner controlled by computer, a CCD video camera, and software for image analysis. A fringe-recognition algorithm determines the spacing and orientation of the fringes and permits the calculation of the magnitude and direction of the displacement of the analyzed object point in images with variable degrees of illumination. For a 256 x 256 pixel image resolution, the procedure allows one to analyze from three fringes to a number of fringes that corresponds to 3 pixels/fringe.     

Vector representation of Moiré fringes

Moiré fringes are represented as vectors and their characteristics established using vector algebra. It is shown that the Moiré fringe vector of deformation is the vector sum of those due to extension and rotation.>     

Code counting of optical fringes: methodology and realization

A new optical fringe-counting method that entails coding interference fringes is proposed. This method features not only the implementation of reliable bidirectional optical fringe counting but also the accurate counting of oscillating optical fringes. Its main merit is the achievement of a higher phase resolution, lambda/16 (lambda, wavelength), as opposed to lambda/8 of earlier fringe-counting methods. The robustness of fringe-code counting with regard to relative phase variations in the sine and cosine interference signals constitutes another merit of this method. The principle and realization circuit of the fringe-code-counting method are described in detail, and the experimental results with a resolution of lambda/16 are presented to show the feasibility of this method.     

Errors in film refractive-index determinations from interference fringes

An analysis of interference fringes (channel spectra) in transmission or reflection spectroscopy of optical films can provide an accurate method for determining the refractive index or thickness of the film. If the index is changing and the common equation n = 1/(2tΔv) determined from the positions of two adjacent maxima in the interference pattern is employed, the resulting refractive index does not lie between the correct values at the frequencies of the two maxima as intuitively expected but well outside this range. This error can be large and is not restricted to the previously discussed case of an index with a linear dependence on wavelength.     

光栅莫尔条纹细分及辨向方法研究

提出了一些新的基于数字处理技术的莫尔信号细分及辨向方法.单光栅副莫尔条纹采用差值细分方法;双光栅副莫尔条纹采用乘积细分法.将信号进行区间划来实现辨向.实验采用DSP器件内置的高速A/D模块实现数/模转换,利用DSP专用指令实现信号的滤波、细分和辨向.实验结果表明,单光栅副和多光栅副的细分精度分别为3"和0.3".     

Polygon approximation of the fringes of diffractive elements

In the electron-beam fabrication of interferogram-type diffractive elements, such as diffractive lenses, continuous fringes are often approximated by polygons to reduce the data volume. Local wave-front errors are then generated that scatter light and give rise to background noise. A roughness parameter beta is introduced to quantify local phase errors in polygon-encoded diffractive structures. An efficient numerical method is developed to compute the Fresnel diffraction pattern of a polygon aperture. Polygon-approximated diffractive axicons and lenses are then investigated to determine the dependence of the signal fidelity on beta. It is found, e.g., that the maximum local phase error must be as large as pi/6 rad before the Strehl ratio S of a paraxial diffractive lens reduces below S = 0.9. However, much smaller errors can noticeably break the circular symmetry of the diffraction pattern.     

Multiple rotation assessment through isothetic fringes in speckle photography

The use of different pupils for storing each speckled image in speckle photography is employed to determine multiple in-plane rotations. The method consists of recording a four-exposure specklegram where the rotations are done between exposures. This specklegram is then optically processed in a whole field approach rendering isothetic fringes, which give detailed information about the multiple rotations. It is experimentally demonstrated that the proposed arrangement permits the depiction of six isothetics in order to measure either six different angles or three nonparallel components for two local general in-plane displacements.     

Interferometric array illuminator with analysis of nonobservable fringes

Interferometric methods for array generation offer various advantages over diffractive methods. Use of polarizing elements in an interferometric array illuminator results in interesting properties in addition to improving the efficiency considerably from low levels. The array pattern appears as nonobservable fringes that can be observed only with a polarizer, and the interferometer is insensitive to one of the tilt components. A thorough analysis of such an interferometric array illuminator is presented in this paper. Several possible applications of such an interferometer in addition to use as an array illuminator are proposed.     

Crack-tip isochromatic and isopachic fringes at a bi-material interface

The optical evaluation of the stress intensity factors and the distribution of the principal stresses from isochromatic and isopachic fringes is presented. The stress intensity factors and the principal stresses at the bi-material interface crack-tip are experimentally determined using the comparison photoelastic and isopachic measurements. The size and the shape of crack-tip isochromatic and isopachic fringes, at a bi-material interface under static load, are studied. When the crack-tip, which is perpendicular to interface, is at the interface of the bi-material, the isochromatic and the isopachic fringes depend on the properties of the two materials. Thus, the isochromatic and the isopachic fringes are divided into two branches. The size of the two branches mainly depends on the elastic modulus and the Poisson’ s ratio of the two materials.     

Interpretation of fringes obtained with coherent gradient sensing

An interference analysis for double-grating shearing interferometry called coherent gradient sensing is presented, and the results are compared with an earlier geometrical optics analysis and a Fourier optics analysis based on the Fresnel approximation. The influence of the order of approximation in these analyses and the equivalence of fringe interpretation in each case are discussed.