Visual characteristics of inhomogeneous acoustic waves

Experimentally obtained visualizations of propagating inhomogeneous acoustic waves driven by zero-order antisymmetric Lamb waves (flexural waves) in water are presented. The inhomogeneous waves are visualized by optical holographic interferometry. A series of photographs show the evolution in time of instantaneous acoustic pressure distributions associated with propagating inhomogeneous waves. The photographs reveal characteristic features of flexurally driven inhomogeneous waves such as transversely attenuated wavefronts oriented perpendicularly to the plate boundary and a phase propagation velocity along the boundary approximately equal to the plate wave velocity (250 meters/second). Effects due to the dispersive nature of the flexural plate waves are also noted in the photographic series. Features distinguishing these subsonic, inhomogeneous surface waves (also called trapped or evanescent waves) from the leaky, lateral or head wave and also from incompressible fluid motions associated with low frequency vibrations of fluid loaded plates are identified. The relevance of inhomogeneous acoustic waves driven by subsonic flexural waves to practical sound-structure interaction problems is discussed.     

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.     

Four-pulse interferometric recordings of transient events by pulsed TV holography

With traditional double-pulsed holographic interferometry or pulsed TV holography, the experiment usually has to be repeated to allow the recording of a time sequence of interferograms of the event. With the proposed technique a sequence of four interferograms of a solitary transient event is measured. A twin oscillator, injection-seeded, pulsed Nd:YAG laser is incorporated into a pulsed TV holography set-up. With orthogonal polarisation and double pulsing of each of the two channels of the laser, four pulses are recorded on two separate CCD-frames. Four interferograms of a laser-impacted plate obtained from the same experiment, show how the bending waves develop and propagate in the plate.     

Comparison of double-pulse digital holography and HPFEM measurements

Pulsed digital holographic interferometry is a widely used technique for measurement of surface deformations. The results are displayed as high-quality images containing the surface deformation represented as a continuous function with high-precision and good resolution. On the theoretical side, the high precision finite-elements method (HPFEM) can be used to compute whole deformation maps of elastic continua, with a resolution comparable to that obtained with digital holographic interferometry. To prove the latter a series of resonant modes from a flat rectangular metal plate obtained with digital holographic interferometry will be compared to the same modes obtained under the same conditions with HPFEM. A very useful measurement concept is reached by combining both methods since they can be performed in parallel and within the same working area.     

Recording receptance of flat plates by holographic interferometry

In the study of mechanical vibrations of structures, the complex ratio of the displacement of the structure at a point divided by the force input to the structure at the same point or a different point is called receptance. This ratio is usually recorded in magnitude and phase by using piezoelectric transducers attached to the structure. This paper describes a study of the feasibility of recording the displacement of a square cantilevered plate not just at one point but over the entire plate surface, by using holographic interferometry. For purposes of comparison of the two techniques a piezoelectric transducer was attached to a free corner of the plate and the displacements at that point were recorded over the frequency range of interest. Although the dynamic range of the holographic technique was found to be somewhat limited, it was found that it is quite feasible to calculate at least the magnitude of the receptance by recording displacements holographically. Since the holographic fringe formation is an integrated effect in time, it was not possible to record the phase by holographic means. The displacements recorded at the corner of the plate by the two methods agreed very well.     

Real-time holographic interferometry using photorefractive sillenite crystals with phase-stepping technique

This work presents a holographic interferometer that uses the photorefractive sillenite crystals in diffusive regimen whose configuration exhibits diffraction anisotropy for real-time holographic interferometry. The writing–reading process of holographic interferogram was done in real-time, connected with an interferogram-analysis method that uses the phase-stepping technique for quantitative measurement of changes on an object. The holographic interferograms from the analyzed surface were captured and they were used to calculate the phase map with four-frame technique. The unwrapping process used was the cellular-automata technique. We obtained quantitative results for some applications: measurements of micro-rotation of surfaces, punctual micro-displacements on an aluminum plate, stress on a dog's jaw, among others; adding new promising applications possibilities for basic research, dentistry and technological areas.     

光纤全息散斑干涉计量

脉冲激光经光导纤维传输后，其偏振性变化为随机分布，相干性有所降低，但它用在全息干涉计量中却有突出的优点，对于涉条纹的形成和清晰度没有影响。经常使用的光纤散斑全息干涉系统有两种类型：一种是只用传光束形成物光，参考光，此种系统形成的全息象清晰度有所下降，但做全息干涉计量时对条纹的衬比度和清晰度没有任何影响．另一种类型是物光和参考光都是用光导纤维传输，然后用光纤传象束将物体的象进行传输，再用透镜将其成象在底片上，做双曝光全息干涉时则形成全息散斑干涉计量，用全息方法再现时干涉图类似“杨氏”条纹。本文对上述两种系统，结合实验结果、分三种情况进行了研究。文章共分为三个部分：（一）引言；（二）散斑全息干涉计量；（三）结论。     

二次曝光全息术在圆柱形冲击波会聚过程观测中的应用

本文对全息曝光技术进行了分析,设计了一种全息干涉仪,对圆柱形冲击波会聚过程的不稳定性进行了观察,并得出了几个有重要价值的结论。     

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.     

Digital phase shift holographic interferometry and its application in the experimental flow study

The application of digital phase shift holographic interferometry to flow-visualization and flow temperature measurement of a 2D thermal flow field was experimentally investigated. An improved recording system for two reference beam phase shift holographic interferometry is set up for this experiment, and details of this experimental technique are described. The phase distribution obtained by this technique presents an excellent picture of flow visualization. From this phase image, temperature distribution of the 2D thermal flow field is also calculated and compared with some measured values obtained using thermocouple probes.     

The measurement of residual stresses by sandwich holographic interferometry

Sandwich holographic interferometry was first proposed by Prof. N. Abramson in 1974. There are many advantages in using this method. One of its most important virtues is that it can compensate for rigid body displacements between the two exposures and is very convenient in practical operation. The authors have already made a detailed theoretical analysis of in-plane and out-of-plane displacements. This paper describes experimental measurements of the residual stresses in welds, by studying the curvature or the second-order derivative of the fringes of in-plane or out-of-plane displacements, using sandwich holographic interferometry. The stresses are obtained quantitatively, and are verified by an experiment involving measurements of the stresses of a flat plate.     

利用压电移相器判别物体变形方向

本文提出了一种在实时全息干涉计量术中利用压电移相器判别物体形变方向的简单而可靠的方法,文中给出了它的原理和实验验证.     

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.     

Measurement of properties of silver telluride thin films using holography

Holography is an interferometric method of recording the light waves diffracted by a subject illuminated with coherent light. Holographic interferometry (H.I.) is one of the most important applications of holography. It is concerned with the formation and interpretation of fringe patterns, which appears when a wave generated at some earlier time and stored in a hologram is later reconstructed by interfering with comparison wave. We report a technique, which uses double exposure holographic interferometry together with simple mathematical interpretation, which allow immediate finding of stress and thickness of thin film. We tested the same for different normalities of solutions. It was further noticed that the fringe spacing changes with solution concentration as well as time of deposition. The thin films are prepared using electrodeposition technique. It’s structural, morphological and optical study carried out by XRD, SEM, and UV-Vis-NIR spectrophotometer.     

Coherent optical measurement techniques in profilometric determination of local mass transfer coefficients

Some measurement techniques using a coherent light source in profilometric determination of local mass transfer coefficients are described in this paper. Different optical setups for holographic interferometry coupled with the two basic profilometric techniques: the swollen polymer technique and the sublimation technique, are described in detail. Finally, the application of electronic speckle pattern interferometry to profilometric measurements is also discussed.     

Holography and electronic speckle pattern interferometry in geophysics

Geophysical applications of holography and ESPI are reviewed. First, laboratory experiments of rock deformation and failure with holographic interferometry and holographic in situ stressmeters are briefly summarized. Then, holographic measurements of tunnel deformations made in Japan are described. The holographic recording system, consisting of an He---Ne gas laser and associated optical elements, was installed in a tunnel at the Amagase Crustal Movement Observatory, Japan in 1984. Tunnel deformations caused by tidal and tectonic forces have been precisely determined using the ‘real-time’ technique of holographic interferometry. Finally, some attempts to apply ESPI to geophysical measurements are introduced.     

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     

电子学全息干涉术用于温度场测量

探讨了用电子学全息干涉术（双称数字全息干涉术）测量温度场分布及其变化的可行性，利用所设计的全息干涉实验光路，对一电烙铁头部周围温度场分布进行了实时全息记录，进而利用一维快速傅里叶变换及数字滤波处理再现出了反映温度场分布的全息干涉条纹图样，实验结果表明，与传统的光学全息干涉术相比，电子学全息干涉术借助于高分辨率CCD记录及高速计算机数字处理技术，从而可实现光学全息图的数字化记录、存储和重现。同时，利用再现物场相位倍增原理还可实现对干涉条纹数目的倍增，或利用物场相位分布的直接计算精确获取任意两点间的相位差，从而提高测量精度。此外，由于能够在不改变光路的前提下以较高的重复频率完成光学全息图的记录，电子学全息干涉术可以用于记录三维物场的变化并接近实时地再现和测量三维物场的变化规律，因此是一种极有发展前途的新型实时全息干涉计量技术。     

物面单反射镜波前分割三光束全息干涉计量研究

提出了一种用于分析物体三维位移场的全息干涉计量新方法。该方法将一个小平面反射镜贴于被测物体的表面，用三束呈空间分布的发散光波，在干版的三个不同区域或同一部位，记录被测物体的三个独立的双曝光干涉图。这些干涉图被由小平面反射镜运动造成的参考光虚点光源的位移所调制。基于对这种调制的理论分析，导出计算参考光虚点光源和被测物体三维位移的二个线性方程组。     

Light-induced lens analysis in photorefractive crystals employing phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities of phase-shifting real-time holographic interferometry for the analysis of light-induced lens in photorefractive and nonlinear optical materials. We show that this technique can be used for quantitative evaluation of the phase distribution of a wavefront changed by a light-induced lens and, consequently, the refractive index changes in these materials. The basic principle of this technique combines real-time holographic interferometry with phase-shifting technique for interferogram analysis. This method is demonstrated with in situ visualization, monitoring and analysis in real-time and uses a Bi₁₂SiO₂₀ crystal as the holographic medium and a Bi₁₂TiO₂₀ as the test sample.