Digital holographic interferometry based on wavelength and angular multiplexing for measuring the ternary diffusion

We present a novel method for dynamical measurement of the ternary diffusion by using digital holographic interferometry based on wavelength and angular multiplexing techniques. Two laser beams with different wavelengths (λ1=532 nm and λ2=473 nm) are used for the ternary diffusion measurement, and they are adjusted to make corresponding interference fringes in orthogonal directions on the CCD target. The orthogonal splitting of the fringes enables the spatial frequencies of each wavelength to be filtered separately in the Fourier spectrum of the hologram. Finally, they are reconstructed to obtain the molar concentration. This method is also suitable for two-phase diffusion measurement.     

基于莫尔理论的双波长全息干涉术分析

当用双波长全息干涉术通过单次曝光法或双曝光法对物体进行测量时 ,其效果相当于用一个等效波长λeq=λ1 λ2 /|λ1 -λ2 |对物体进行测量 ,扩大了测量波长的可选范围。采用莫尔理论从一个全新的角度对双波长全息干涉术的基本原理进行了分析和探讨 ,不仅揭示出了二者之间存在着的必然内在联系 ,而且还进一步证明了双波长全息干涉术的准确性和可行性 ,从而扩展了双波长全息干涉术的应用领域     

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.     

Digital holographic interferometry applied to the study of tympanic membrane displacements

Quantitative studies of the mechanical properties of tympanic membrane (TM) are needed for better understanding of its role in detailed clinical evaluation, its research being of extreme importance because it is one of the most important structures of the middle ear. By finding the membrane's vibration patterns and quantifying the induced displacement it is possible to characterize and determine its physiological status. Digital holographic interferometry (DHI) has proved to be a reliable optical non-invasive and full-field-of-view technique for the investigation of different mechanical parameters of biological tissues, i.e., DHI has demonstrated an ability to detect displacement changes in quasi-real time and without the need to contact the sample's surface under study providing relevant information, such as clinical and mechanical sample properties. In this research fresh tympanic membrane specimens taken from post-mortem cats are subjected to acoustic stimuli in the audible frequency range producing resonant vibration patterns on the membrane, a feature that results in an ideal application for DHI. An important feature of this approach over other techniques previously used to study the tympanic membrane vibrations is that it only requires two images and less hardware to carry out the measurements, making of DHI a simpler and faster technique as compared to other proposed approaches. The results found show a very good agreement between the present and past measurements from previous research work, showing that DHI is a technique that no doubt will help to improve the understanding of the tympanic membrane's working mechanisms.     

Dynamic measurement by digital holographic interferometry based on complex phasor method

In this paper, complex phasor (CP) method is employed in digital holographic interferometry. Unlike commonly used digital phase subtraction (DPS), the proposed technique processes a CP instead of phase. It is shown that the results obtained by directly filtering the phase produce large errors. It is demonstrated that the phase is not a signal but rather a property of a signal. In addition, the results obtained by the CP method are also compared with those obtained by conventional sine/cosine transformation method.     

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.     

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.     

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。     

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.     

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.     

Self-referenced spectral interferometry

A new femtosecond pulse characterization, named self-referenced spectral interferometry, is introduced. Based on linear spectral interferometry, the reference pulse is self created from the pulse being characterized. This self reference results from pulse shaping optimization and non-linear temporal filtering.     

XeCl discharge diagnostic by holographic interferometry

A direct measurement of the electron-density time evolution in the active medium of a self-sustained XeCl laser discharge has been performed by means of the holographic interferometry technique. The time and space resolved behaviour of the discharge seems to confirm that the halogen depletion instability and the hot spots developing in the cathode region are the basic mechanisms which determine the premature termination of the output laser pulse.     

用全息干涉法测量杨氏模量

通过对悬臂梁受力前后双曝光全息图进行再现，测量出干涉条纹序数与相对应的位置坐标，再利用最小二乘法求杨氏模量．     

Attosecond spectral shearing interferometry

We show that the complete characterization of arbitrarily short isolated attosecond x-ray pulses can be achieved by applying spectral shearing interferometry to photoelectron wave packets. These wave packets are coherently produced through the photoionization of atoms by two time-delayed replicas of the x-ray pulse, and are shifted in energy with respect to each other by simultaneously applying a strong laser field. The x-ray pulse is reconstructed with the algorithm developed for optical pulses, which requires no knowledge of ionization physics. Using a 800-nm shearing field, x-ray pulses shorter than approximately 400 asec can be fully characterized.     

Diffusion studies in liquids by holographic interferometry

Liquid diffusion coefficients are very important basic data for research and many applications in chemical engineering and in other fields, such as biological systems, pollution control and separation of isotopes. Holographic interferometry technique with accuracy and promptness is one of the most widely used techniques for diffusivity studies. We report an interferometric technique to determine the diffusion coefficient of transparent liquid solutions. As the diffusion progresses with time the refractive indices at different planes in the cell are different, and the characteristic extreme points of the fringe patterns shift outward. The interference fringes was obtained and recorded on a PC using a CCD camera. By judging the interferogram with a computer procedure the concentrations at different planes can be obtained by the relation between concentration and refractive indices, furthermore, the diffusion coefficient can be obtained by calculation. The obtained diffusivity values matched very well with the existing experimental results.     

Measuring the displacement vector by holographic interferometry

Triple exposure holographic interferometry provides knowledge of the displacement vector. Between the first two exposures the object is displaced by a calibrated amount, and before the last exposure it is translated by an unknown amount.