Three-dimensional flow visualization system by holographic interferometry

A holographic system has been developed to visualize a three-dimensional fluid flow. The system consists principally of a thermoplastic film, a monochrome video camera, a microcomputer with image-processing capability and a printer. The system makes it possible to measure a slow flow. Two examples of such, the bimodal and mixed-mode convection flows within a Bénard cell, are presented.     

All-around holographic three-dimensional light field display

Technology for all-around holographic three-dimensional (3D) light field display is proposed in this paper. A plane mirror keeps rotating around the optical axis. At each angular position, the mirror-image's Fourier CGH of the target object is projected onto the mirror. The reflected CGH contributes a specific viewing angle range to the target object. Linking up all viewing angle ranges in the horizontal plane, all-around display can be realized via the “afterimage” effect. An all-around holographic 3D light field display is implemented experimentally here with a 60 Hz SLM by introducing an observer tracking unit in the proposed display system.     

Real-time analysis of 3-D axisymmetric refractive index field by photorefractive holographic interferometry

A real-time test method for determining the refractive index distributions of 3-D axisymmetric temperature field around a flame with the use of a photorefractive holographic interferometer is proposed. Some techniques in data processing for improving the quality of resultant interferogram are developed. Experimental results, which show the effectiveness of this method and agree with theoretical expectations, are also given.     

全息干涉计量中干涉计量场的统计特性

本文运用统计学方法推导了全息干涉计量中散斑计量场的统计特性.证明了:干涉计量场的复振幅为复圆高斯随机变量;干扰计量场强度的概率密度服从负指数分布;散斑干涉计量场的系综平均值代表变形信息.     

Rainbow holographic interferometry

A one-step rainbow holographic process is applied to holographic interferometry. Experimental demonstrations of double exposure and time-average interferograms are included. Comparison is made with the conventional holographic process. We found that the rainbow process provides better equality and less speckle noise.     

Wave optics analysis by phase-shifting real-time holographic interferometry

The purpose of this work is to study the potentialities in the phase-shifting real-time holographic interferometry using photorefractive crystals as the recording medium for wave-optics analysis in optical elements and non-linear optical materials. This technique was used for obtaining quantitative measurements from the phase distributions of the wave front of lens and lens systems along the propagation direction with in situ visualization, monitoring and analysis in real time.     

Temporal phase retrieval from a complex field in digital holographic interferometry

We describe a novel method of processing complex phasors in digital holographic interferometry (DHI). Unlike the commonly used digital phase subtraction method that operates on the phase itself, the proposed method operates on the complex phasor instead. Two temporal phase retrieval algorithms are developed in which the complex phasor of each pixel is measured and analyzed as a function of time. The developed algorithms are demonstrated in profile measurement of step heights. Experimental results show that the proposed phase retrieval algorithms for DHI perform well compared with conventional methods.     

Quantitative visualization of the laser induced plume behavior using quasi-heterodyne holographic interferometry

It is very important that we understand the dynamic behaviors of the laser induced plume in welding, because the laser induced plume has considerable effects on welding efficiency and the quality of materials. Many experimental studies have been performed in order to observe the plume behaviors using a visualization method. In this paper, we describe the visualization and quantification of the laser induced plumes by pulse holographic interferometry. A pulsed Nd:YAG laser was used for the generation of laser induced plume and a Q-switched Ruby laser was employed to record the weld plume. For qualitative visualization of the laser induced plume, we used the double-exposure holographic interferometry. Then, we chose the quasi-heterodyne holographic interferometry with the dual-reference-beam and phase shifting in order to visualize the plume quantitatively. The experimental results show the visible behavior of the laser induced plume according to a change in the output power of the pulsed Nd:YAG laser and the time delay of Q-switched Ruby laser. Finally, we obtained the quantitative results by using the dual-reference-beam.     

Analogue difference holographic interferometry for two-wavelength contouring

Difference holographic interferometry uses holographic illuminations from the master object for the illuminations of the test object. The principle has been applied successfully for deformation measurement, phase object investigation and for contouring, as well - but in the last case within the two-refractive index method, only. Its application for contouring with the two-wavelength method is still missing - although it does exist already in the much later developed digital holographic interferometry.The present paper resolves this discrepancy and provides the better “analogue quality” by reporting the first realization of the analogue difference holographic interferometry in the two-wavelength contouring. Experimental evidence is presented not only for the existence of the application but for the numerical correctness of difference making, too. The measuring range extension achieved is threefold.     

三维温度场的激光全息与干涉层析

本文论述了多方向干涉层析再现三维温度场的原理,提出了多方向象面全息干涉法,并利用这种方法测量了三维温度场分布;进一步提出了一种更有实用价值的多方向法布里-珀罗干涉法,它具有实时性,能用于真实瞬态流场的测量.     

Quantitative analysis of holographic particle data

There are several well known difficulties in forming and analysing holographic particle data in the micrometre and submicrometre size range. This paper suggests that these problems can be overcome by using a combination of research techniques. Firstly, it has been found that it is possible to record images of submicrometre particles by using conventional photographic materials. Essentially, a diffraction limited optical component has been used to provide aberration free particle images. Secondly, the sensitivity of the holographic material has been increased with the use of specialized holographic processing chemicals. Thirdly, it has been found that it is possible to encode holographically double, slightly displaced, particle images by using a pulse laser. Thus, Young's fringes can be obtained directly from the stored holographic data, and the particle velocity can be measured directly from the hologram. Fourthly, the holographic particle data can be automatically analysed, using a software program. Finally since the data is stored holographically, it is possible to obtain instantaneous 3-D particle velocities. This paper demonstrates that it is possible to perform holographic particle image velocimetry automatically, with only a small amount of preprocessing.     

双波长全息干涉计量分析

本文分析和讨论了双波长全息干涉计量的单次曝光法和双曝光法。这两种方法都提供了用可见光得到相当于不可见的长波干涉的结果,其测量灵敏度和测量精度可以通过选择合适的工作波长而能得到调整。     

Fixed Q pulsed holographic interferometry

Continuous wave laser time-averaged type holographic interferometry has long been used for the analysis of structural vibrations. The exposure time is usually much larger than the vibration period. The brightest interference fringe corresponds with the nodal region, i.e. that portion of the surface that remains stationary during exposure. The application of the technique is, however, like all continuous wave laser holography, limited to structures that can be observed in a vibration free environment.The output of a ruby laser oscillator in use at Marchwood Engineering Laboratories (MEL) consists of a random series of spikes contained in an envelope of about 800 μ. The coherence length of the output is greater than 1 m. Use of this output allows the production of time-averaged holograms in unstable environments. Due to the random nature of the output, the fringes are not readily quantifiable but show the characteristic bright zero-order fringe of continuous wave time-averaged holography.     

Aberration-free lateral shear holographic interferometry

Lateral shear interferometry is considered as a possible means for optical correction of wave fronts reconstructed from singly and doubly exposed holograms. Optical aberrations are eliminated in a moiré pattern by superposing two lateral shear interferograms using waves diffracted by original holograms. It is shown that the singly exposed hologram allows compensation for only optical inhomogeneities due to the substrate, while the doubly exposed hologram also excludes aberrations due to the recording system. The experimental results supporting the efficiency of the method as applied to imperfect substrates of holograms are presented.     

Reference fringes in holographic interferometry

This paper describes the application of reference fringes in double exposure holography of transient phase objects. This includes selection of fringe patterns and fringe number densities suitable for the quantitative analysis of the hologram. Methods of realizing different reference fringe patterns are presented. As the focus of the interference fringes depends on the optical arrangement, different systems are discussed.     

Picosecond three-color holographic digital interferometry

The possibilities of multicolor digital holographic interferometry are experimentally studied upon measuring displacements of a surface in radiation of a picosecond Nd:YAG laser with the radiation frequency conversion into harmonics (λ₁ = 1.06 μm, λ₂ = 0.53 μm, and λ₃ = 0.35 μm). It is shown that three-color digital holographic interferometry makes it possible to increase the measurement accuracy of displacements. The peculiarities of multicolor digital holographic interferometry by picosecond pulses are discussed.     

Two-wavelength dispersion holographic lateral-shift interferometry

It is demonstrated that two-wavelength holographic interferometry with a small lateral shift in a grating interferometer makes it possible to study the dispersion characteristics of transparent objects using probe beams with arbitrary wavelengths. Interference patterns reconstructed represent fringes on the reconstructed image of the object, which characterize the value of the derivative of the difference between the refractive indices of the medium under study at the probe wavelengths along the direction of the shift. The results of experiments employing the method proposed are presented.     

频闪相移全息干涉计量

本文将相移技术应用在频闪全息干涉计量中,获得了振动物体的定量分析结果.分析了频闪光脉冲宽度对计算结果的影响,并给出了实验结果.