Extension of the controlled sensitivity range in holographic interferometry with a lateral shear

The possibility of controlling the measurement sensitivity in shearing interferometry with a small lateral shear is considered. A method based on recording several holographic interferograms with different magnitudes of lateral shear and with different carrier frequencies of holographic fringes during a single exposure is proposed. The measurement sensitivity of the interference patterns is controlled at the stage of optical processing of the combined holographic interferograms with lateral shear, when the interferograms are illuminated by two coherent light beams and the filtering of the corresponding diffraction orders is performed. The results of the experimental testing of the proposed method by using it for the visualization of the melting zones of planar polymethylmethacrylate samples under heat treatment are presented.     

Real-time holographic interferometry using superposed compensating holograms

Superposed compensating holograms are shown to be a promising tool for solving a number of problems in real-time holographic interferometry, in particular, obtaining of interference patterns with fixed parameters of reference fringes and adjustment of the measurement sensitivity. The proposed approach is tested through visualization of the melting of a PMMA planar sample by means of lateral shear holographic interferometry.     

Enhancement of measurement sensitivity in determination of changes in the shape of a wavefront by holographic lateral-shearing interferometry

A method for increasing measurement sensitivity in the visualization of dynamics of changes in wavefront shape with the use of holographic lateral-shearing interferometry is considered. At the first stage of this method, a photograph of a reference shear interferogram obtained with tuning to closely spaced fringes is recorded under linear conditions. After chemical treatment, the photograph of the reference shear interferogram is installed in exactly its initial position. At the second stage, a series of photographs of lateral-shear interferograms of the wavefront under study is recorded under nonlinear conditions using the photograph of the reference interferogram. The photographs of the lateral-shear interferograms are optically processed by two coherent beams with selection of the highest diffraction orders, which makes it possible to visualize the dynamic component of the wavefront deformation with an increase in the measurement sensitivity (the static component is excluded in this case). The effect of the degree of nonlinearity of photograph recording on the range in which the measurement sensitivity can be controlled during the optical processing of a pair of matched photographs or one double-exposure photograph of interferograms recorded at different values of a lateral shift is analyzed.     

用实时全息术研究低速变化过程的一种简易系统

研制了一种用于研究物体低速过程的简易系统，它由带有液门原位化学处理的实时全息干涉装置和具有连拍功能的相机以及一台氦氮激光器组成，是一种简易实用的“低速、实时全息干涉摄影系统”。用它记录了火箭推进剂样品在室温，常压下的燃烧过程，１００瓦普通只灯逐级加压的点燃过程，对实时全息图的记录和处理采用了一种可获得高反衬度的新技术，拍摄的成功率高，干涉条纹的反衬度好，它为研究物体的低速变化过程提供了一种有力的手     

Reduction of the error in measuring the wedge angle of transparent plates in holographic reverse-shearing interferometry

To reduce the error in measuring small wedge angles of transparent plates by holographic reverse-shearing interferometry, it is proposed to form a pair of interference patterns using joint plate rotation and alternate tuning to an infinitely wide band in the right and left patterns. The results of experimental approval of the method used to form interferograms of a glass plate with a small wedge angle, which indicate a higher sensitivity of this method and, as a consequence, a smaller measurement error, are presented.     

Recent contribution in color interferometry and applications to high-speed flows

Recent improvements brought to color interferometry for analyzing high-speed flows are described through different applications. First, the optical technique based on differential interferometry using a polarized white light and one or two Wollaston prisms allows to record high-speed interferograms of the flow downstream of a circular cylinder. Then, this technique has been applied to axisymmetric flows for studying an interaction between a supersonic hot jet and a coaxial supersonic flow. Another application concerns the study of hypersonic flows using Wollaston prisms with a large birefringence angle. Finally, the analysis of gaseous mixture and the evolution of two-gases interface submitted to an acceleration is presented. Interferograms analysis is made from a modeling of interference fringes versus the optical path difference which allows to easily extract quantitative information of the gas density. In order to obtain absolute measurements of the gas density, real-time holographic interferometry has been developed using a three-color laser source and a panchromatic holographic plate. The technique generates the achromatic white fringe which makes the zero order of interference fringes easy to identify. An application is presented in a 2D subsonic wind tunnel, in which the unsteady wake flow past a cylinder is recorded at high framing rate. In this optical setup, transmission holograms are used. As a conclusion, an approach is proposed to analyze the 3D flows from real-time color holographic interferometry using reflection holograms and the problems to solve are described.     

High-sensitivity holographic interferometry method for studying transparent objects with small transverse size

A new method for studying transparent objects with a small transverse size is considered. The method is based on lateral-shift holographic interferometry combining the displacement of the transparent object under investigation between the recordings of a pair of holographic interference patterns and their optical treatment. The interference patterns of the transparent object under investigation with a lateral shift equal to or larger than the linear size of the object are equivalent to the interference patterns obtained in a double-beam interferometer with a reference wave. In addition, such patterns are characterized by a higher sensitivity of imaging of optical inhomogeneities of the object under investigation. The results of experiments on testing this method for monitoring optical inhomogeneities of the active medium crystal of a solid-state laser are reported. The resultant interference patterns depict optical inhomogeneity of the crystal with a sensitivity 12 times higher.     

Enhancement of sensitivity of measurements of the holographic lateral-shear interferometry in studies of fast processes

The possibility of enhancing the sensitivity of measurements upon visualization of temporal variations of a phase object by means of optical processing of the holographic lateral-shear interferograms, without the necessity of detecting the original holographic interferograms under nonlinear conditions, is considered. In rewriting the original holographic interferogram, it is advisable to change the orientation of the holographic fringes and to record the secondary holograms under nonlinear conditions. The proposed method for increasing the sensitivity of measurements was used to visualize variations of thickness of a polymethyl methacrylate plate in the course of its thermal treatment.     

Application of holographic addition and subtraction to quadratic motion analysis

Hologram interferometry of objects moving with constant acceleration has been investigated with special reference to the techniques of holographic addition and subtraction, which results in an extension of the range of measurement of conventional time average holography. Distribution of intensity in the fringes has been plotted for some typical cases.     

Increase in the sensitivity of holographic reverse shearing interferometry due to the combination of object rotation with optical processing of holograms

It is shown for the holographic reverse shearing interferometry, which is used in investigations of phase objects with limited sizes, that combination of rotation of the object under study during hologram recording with subsequent optical processing of a pair of matched holograms makes it possible to obtain, with a much higher sensitivity, aberration-free interference patterns reflecting the changes in the wavefront induced by the object studied. The results of the experimental testing of the proposed method for the cases of optical processing of matched and optically conjugate reverse shearing holograms are reported.     

Real-time color holographic interferometry devoted to 2D unsteady wake flows

A new optical technique based on real time holographic interferometry in true colors has been implemented around the transonic wind tunnel of the ONERA-Lille center to analyze 2D unsteady wake flows. Tests realized in color interferometry, real time and double exposure, use simultaneously three wavelengths of a continuous waves laser (argon and krypton mixed) and holograms are recorded on silver-halide single-layer panchromatic Slavich PFG03c plates. The very principle of real-time true color holographic interferometry uses three primary wavelengths (red, green and blue) to record, under no-flow conditions, the interference among the three measurement beams and the three reference beams simultaneously on a single reference hologram. After the holographic plate is developed, it is placed on the test setup again in the position it occupied during exposure and the hologram is illuminated again by the three reference beams and three measurement beams. A flat, uniform color can then be observed behind the hologram. So a horizontal, vertical, or even circular fringe pattern can be formed and the achromatic central fringe can be made out very clearly. The single color is used to determine the path difference zero on the interferograms. The flow studied was the unsteady flow downstream of a cylinder placed crosswise in the test section. A sequence of hundred interferograms was recorded on the flow around the cylinder at Mach 0.37. The vortex formation and dissipation phases can be seen very clearly, along with the fringe beat to either side of the cylinder.     

A method for increasing the sensitivity of determination of the wavefront distortion in optical processing of holographic lateral shear interferograms

A method for obtaining interference patterns of increased sensitivity in optical processing of holographic lateral shear interferograms recorded under linear conditions at a shear exceeding the size of a phase object under study is proposed. Cases of reconstruction of interference patterns of increased sensitivity using matched and optically conjugate holographic lateral shear interferograms are considered. It is shown that two-and fourfold increases in sensitivity, respectively, are obtained in these cases. The validity of the method proposed is confirmed experimentally     

Evaluation of a method to determine interferometric phase derivatives

A recently published method for the determination of phase derivatives maps by direct manipulation of three or more phase-shifted interferograms is tested for accuracy. The method is evaluated on computer-simulated holographic and electronic speckle pattern interferometry fringes and the results are assesed through the calculation of two comparative parameters: the relative image difference and the linear correlation coefficient. It is shown that errors in the phase derivative strongly depend on the filtering method used for smoothing the fringe patterns. An experimentally recorded ESPI fringe pattern is used to confirm the predictions of the numerical simulations.     

Shearing interferometry using lateral shears in opposite directions

Different schemes of recording shearing interferograms using shears of wave fronts in opposite directions are considered. It is shown that interference patterns depicting the derivative of the wave front phase with an increased sensitivity can be obtained both on separate carriers and on one common carrier without nonlinear recording of a pair of interferograms. Results of experimental verification of the method including a series of interference patterns with sensitivity increased by two times and different tuning of fringes are given.     

Application of correlation speckle photography for measuring contact pressures

A method for measuring contact pressures based on the measurement of irreversible changes in a surface microrelief by the speckle photography technique is presented. The analytic dependence between the change in the contrast of the carrying Young’s fringes and the relative area of change in the microrelief is considered. An example of a contact interaction between a cylinder end and a flat slab, the latter with a specially produced regular roughness on its contact surface, is used to experimentally verify the relation between the irreversible change in the roughness, the change in the contrast of the holographic interference fringes, and the change in the contrast of the carrying Young’s fringes. It is shown that the sensitivity of correlation speckle photography is higher than the sensitivity of the correlation holographic interferometry technique.     

Dual hologram interferometry

This report describes dual hologram interferometry, a new electro-optic technique used to calculate two-dimensional density distributions from measurable changes in index of refraction. Using this technique, two scenes recorded at different times are stored in separate holograms. One hologram contains reference data depicting the subject in an undisturbed state and the other hologram describes the same subject in a test or disturbed condition. Desired interference patterns are obtained by super-imposing the two separate scenes which are simultaneously reconstructed from each hologram. Specific interferograms, infinite fringe and various finite fringe patterns, are obtained by carefully regulating the optical attitude between the holograms and the reference beam during reconstruction of the scenes. In this project, dual hologram interferometry is used to describe quantitatively free convection from a uniformly heated right circular cylinder. Temperature distributions through the boundary layer and local heat transfer coefficients are determined at different azimuth positions. The results are compared both to experimental data obtained from another holographic technique and to a theoretical prediction of this specific test. This investigation shows that dual hologram interferometry accurately records changes in index of refraction which means the technique can be used to accurately measure experimental fluid flow data.     

二次曝光全息术对微波等离子体推进器羽流的诊断及计算机模拟

二次曝光全息术是诊断等离子体电子数密度的一个有效测量方法,具有非接触式测量及不受等离子体发光干扰等优点.根据阿贝尔变换公式,通过计算机应用matlab程序数值模拟了各种不同电子数密度状态下的等离子体干涉图.同时拍摄了航天器中微波等离子体推进器羽流的二次曝光全息图,再现了不同状态下的干涉图样.通过分析和对比两次干涉图,得出了羽流的电子数密度.     

Application of the holographic carrier fringe and FFT technique for deformation measurement

This paper describes a holographic system based on the use of fibre optics and automatic spatial carrier fringe pattern analysis. Carrier fringes are generated by simply translating the object beam between two exposures. Single-mode optical fibres are used to transfer both the object and reference beams. The fast Fourier transform method is used to process the interferograms: it extracts phase from fringe patterns resulting from the interference of tilted wavefronts. The method is illustrated by measuring the deformation of an arbitrarily clamped, uniformly loaded circular plate. The results are given for the perspective plot of the out-of-plane deformation field, the maps of wrapped and unwrapped phase, and a contour map of the unwrapped phase.     

Sequential hologram interferometry with diffusely illuminated objects

Two simple holographic multiplexing techniques for sequential hologram interferometry of a diffusely illuminated object are described. These techniques enable one to use the frozen-fringe hologram interferometry to study a quasi-continuous change in the object and so regain some of the advantages of real-time hologram interferometry. In the first method of multiplexing with a single reference beam, a small angle prism is used for varying the direction of the reference beam between successive exposures and a double-exposure hologram is recorded at each position of the prism. In the second method of multiplexing with multiple reference beams, a separate reference beam is used for recording each state of the object independently and the interference pattern between any two states is obtained by simultaneous reconstruction of two light fields. The advantage of this method over the previous one is that it is also suitable for dynamic studies. Some reconstructed interferograms of a diffusely illuminated transparent object under different stresses are presented as illustrations.     

Production of holograms with shearing interferometers using a wide light source

Interferograms with narrow fringes obtained with grating and polarization interferometers using a wide source allow the use of some processes of holographic interferometry and schlieren techniques for investigating a reconstructed wavefront. The reconstructed interference patterns of a sphere's supersonic flow are presented. A scheme for obtaining colour schlieren patterns is described.