Holographic Interferometer Research Articles

Adaptive filter algorithms for interference patterns of diffusion measurements

A holographic interferometer is used to measure diffusion coefficients of binary molten salt mixtures. The composition of such transparent mixtures is proportional to the refractive index. The composition changes cause local variations of the refractive index during diffusion. These variations are visualized by interference fringes, which are photographed by a CCD camera. Exact detection of the intensity extreme values of the fringes is essential to calculate diffusion coefficients. As irregular illumination and noise disturb the detection, adaptive filter algorithms are applied to reduce noise sufficiently while maintaining all relevant information.

Measurement of the a.c. impedance of aluminium samples by holographic interferometry

In the present investigation, holographic interferometry was utilized for the first time to measure the alternating current (a.c.) impedance of aluminium samples during the initial stage of anodization processes in aqueous solution without any physical contact. The anodization process (oxidation) of the aluminium samples was carried out chemically in different sulphuric acid concentrations ( 0.5–3.125% H 2SO 4 ) at room temperature. In the mean time, a method of holographic interferometric was used to measure the thickness of anodization (oxide film) of the aluminium samples in aqueous solutions. Along with the holographic measurement, a mathematical model was derived in order to correlate the a.c. impedance of the aluminium samples in solutions to the thickness of the oxide film of the aluminium samples which forms due to the chemical oxidation. The thickness of the oxide film of the aluminium samples was measured by the real-time holographic interferometry. Consequently, holographic interferometry is found very useful for surface finish industries especially for monitoring the early stage of anodization processes of metals, in which the thickness of the anodized film as well as the a.c. impedance of the aluminium samples can be determined in situ. In addition, a comparison was made between the a.c. impedance values obtained from the holographic interferometry measurements and from measurements of electrochemical impedance spectroscopy. The comparison indicates that there is good agreement between the data from both techniques.

Dual hologram shearing interference technique for wind tunnel flow fields testing

A novel optical diagnostic technique, dual hologram shearing interferometry, for measuring density gradients of different phase objects is proposed and demonstrated. The lateral shearing is achieved by using a phase grating. A holographic interferometer has been developed and designed on the base of a single pass Z type conventional schlieren device. The interferometer’s scheme is insensitive to acoustical disturbances, similarly to the conventional schlieren layout, and is capable of recording holograms with a continuous wave laser during the wind tunnel run.

Transient thermal lensing measurement in a laser diode pumped NdxY1−xAl3(BO3)4 laser using a holographic shearing interferometer

A new technique for measuring a thermal lens, using a holographic shearing interferometer is presented. This technique was used to measure transient thermal lensing in a laser diode pumped NYAB laser. The measured thermal lensing power was proportional to the pumping laser diode intensity, with a gradient of 1.1 × 10−1m−1 mm2/W. The transient response time of the thermal lens was 1.5 s, this value being consistent with the temporal decline of the second harmonic power.

Real-time photorefractive interferometer for dynamic phase perturbation by self-interference in LiNbO_3

We propose a simple real-time system and demonstrate its use for measuring dynamic optical phase perturbation. In this system we used a 0.1-wt. % Fe:LiNbO(3) to record the self-interference grating with incident light. The system is a new kind of real-time holographic interferometer. After rise time in the interferometer, the speed for showing the fringes is as fast as that of dynamic phase perturbations. Characteristics of the interferometer are proposed and examined.

Holographic polarization interferometry

A new approach based on the combination of the advantages of holographic interferometry with those of polarization measurements is developed. This approach gives the possibility to apply the polarization method to the investigation of objects which fully depolarize the illuminating light wave. These objects can be presented, for example, by diffusely reflecting surfaces. In the process of realization of this approach, the holographic interferometer becomes the polarization system which is equivalent to a set of single axial crystal plates or optically active media. This system rotates the polarization plane of the object wave at angles, the values and directions of which are proportional to the values and directions of changes of the investigated parameters of the object. As a result, the possibility arises to increase not only the accuracy but also the spatial resolution and informativeness of holographic methods. Different applications of holographic polarization interferometry are also considered in this paper, i.e. for determining the height and direction of surface relief, the values and directions of surface point displacements and for investigating transparent objects.

Real‐time holographic interferometry using optical phase conjugation in photorefractive materials and direct spatial phase reconstruction

The structure and operation of a holographic interferometer that uses photorefractive Bi12TiO20 crystals as reusable recording mate- rials and computer image processing for rapid and precise interpretation of the fringe patterns are discussed. Different types of two-wave and four-wave mixing were applied to optical testing by double-exposure ho- lographic interferometry. A very convenient matching was found in the phase-conjugation setup for the Bi12TiO20 crystals and usual He-Ne la- sers, when the exposures were of ;10 s for light energy densities of 4310 23 W/cm 2 . Simple algorithms and direct spatial phase reconstruc- tion were used for computer image processing of the fringe patterns. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: real-time holographic interferometry; optical phase conjugation; photorefractive materials; fringe image processing; direct spatial phase demodu- lation.

Dynamic holographic interferometry by photorefractive crystals for quantitative deformation measurements

A holographic interferometer that uses two-wave mixing in a photorefractive (Bi12SiO20) crystal under an applied ac field is described. The interferometer uses a repetitive sequence of separate record and readout times to obtain quasi real-time holographic interferograms of vibrating objects. It is shown that a good signal-to-noise ratio of the interferometer is obtained by turning off the object illumination and the applied ac field during readout of the hologram. The good signal-to-noise ratio of the resulting holographic interferograms enables phase measurement, which allows for quantitative deformation analysis.

101 光導電プラスチックによる過渡3次元密度分布の計測

The time sequential measurement technique for three-dimensional density distributions in a channel was evaluated. Using the holographic interferometer, information of the density distributions were visualized as fringes. In the real time method, the wave before disturbance is recorded on a hologram, then the hologram is developed at the initial set position. When the hologram is reconstructed, the fringes are caused by the interference between reconstructed wave of the undisturbed field and wave through the disturbed field. Since the reconstructed wave contains the information of the undisturbed field including the channel surface refraction, the fringe pattern represent only the optical phase changes inside the channel. However it is usually difficult to develop without movement or shrink. Using the photoconductor-plastic processed by solvent vapor, the hologram can be developed without any movement. In this study, buoyancy driven exchange flow of air and helium gas were measured using real time hologram with photoconductor-plastic. The transient three dimensional density distribution of buoyancy driven exchange flow are reconstructed, showing the effectiveness of the proposed technique.

A Study on the Characteristics of Elastic Wave Propagation in Plates Using Double Pulsed Laser Holographic Interferometry

In this paper, the propagation of elastic wave generated by loading impact to plates made of isotropic of anisotropic material was studied. And the influence of boundary conditions (free or clamped edge) upon the reflection of elastic wave was anlyzed. Also, double exposure holographic interferometer using ruby pulse laser was formed in order to investigate transient waves. Before the elasitc wave was reflected from the edges, the elastic wave of isotropic plate such as aluminum plate showed circular interferometric fringe pattern, whereas that of anisotropic plate such as epoxy composite laminates showed elliptical one. And the transverse displacement curves obtained from experiment and theory for both plates agreed well. Also, the waves reflected from the boundary edges showed much differences according to the boundary condition of edges.

Interferometric Tomography Measurement of Spatial Temperature Profiles in Premixed Flame. Application of Dual Plate Fourier Transform Interferometry.

Dual plate Fourier transform interferometry combined with tomographic techniques was investigated to measure three-dimensional temperature profiles in a premixed flame. The dual plate method can overcome several problems and limitations of conventional Fourier transform interferometry. A six-directional two reference beams holographic interferometer is described, with which the conventional contour fringe and the modulated fringe can be obtained simultaneously. The results obtained are as follows. (1) It is not necessary to know the exact value of carrier frequency to extract the phase distribution from a modified interference fringe. (2) The inherent errors caused by the leakage of Fourier spectra and initial phase value are eliminated by its subtraction process. (3) Instantaneous spatial temperature profiles of a laminar premixed flame are presented.

Visualization study on the thermo-hydrodynamic phenomena induced by pulsative heating in He II by the use of a laser holographic interferometer

A visualization method for cryogenic thermo-hydrodynamic phenomena is established by using a laser holographic interferometer. The technique is applied to the study of some transient heat transfer, that is the thermal shock wave propagation and onset of boiling in He II. All these phenomena are induced by a pulsative heating from a thin-film planar heater. The evolution of an initial trapezoidal thermal pulse into a thermal shock wave and the subsequent propagation is visualized at various temperatures. The temperature rise due to diffusive process caused by the action of high density vortices, that is the formation of a thermal boundary layer adjacent to the heater, and subsequent boiling are observed. The finite-amplitude pressure wave is found to be generated in response to the onset of pulsative heating. Further, a visualization of evaporation from an He II free surface caused by the incidence of a thermal shock wave is made and the propagating speed of the vapor front is measured from visualization photos.

Method of heat and mass transfer enhancement in film evaporation

Combined heat and mass transfer processes that occur when water evaporates from a flowing film have been investigated. The major emphasis of this work studied methods to enhance heat and mass transfer rates from the film. A fiber-optic holographic interferometer was used to measure the local heat and mass transfer coefficients from the air—liquid interface, and a set of thermocouples and a dewpoint hygrometer were used to measure the average heat and mass transfer rates in the system. First, without utilizing any enhancement techniques, the local and average transfer rates from the water solution were determined, then a mechanical method for enhancing the heat and mass transfer rates was investigated. In this method, 2 mm glass rods were used to disturb the liquid film flow, which also disturbed the flow of the air stream. The local temperature and concentration distributions were calculated and used to evaluate the local Nusselt and Sherwood numbers. It was observed that average Nusselt number Nu av and average Sherwood number Sh av for the water solution have a maximum which depends on the pitch of the glass rods.

Phase-shifting real-time holographic interferometry that uses bismuth silicon oxide crystals

A bismuth silicon oxide crystal is used in the diffusion regime as a dynamic recording medium in a real-time holographic interferometer based on anisotropic self-diffraction. This device is connected with an interferogram-analysis method that uses the phase-shifting technique for quantitative measurement of diffusive-reflecting object deformations. In addition to the usual error sources in phase shifting, the temporal interferogram erasure is studied and is found weakly perturbative for the measured phase. It is shown that quantitative measurements are possible for low-intensity object beams (8 µW/cm(2)) and a large observed area. Apractical situation of defect monitoring in a composite structure is presented.

Effect of additives on the regeneration of a dilute absorbent

Combined heat and mass transfer processes that occur when a liquid desiccant is regenerated in an opencycle system have been investigated. The experimental setup consists of a channel where an absorbent solution flows over a heated plate and a stream of air flows over the liquid film in a counterflow arrangement. Additives were introduced to a liquid desiccant, a lithium chloride solution, and their effects on the transfer rates were studied using a two-wavelength fiber-optic holographic interferometer to determine the local heat and mass transfer coefficients from the air-liquid interface. The additives selected in this study were a surfactant, anionic sodium lauryl sulfate, and a polymer, anionic poly aery lamide. Nomenclature at = mass fraction of the /th component b = fringe thickness CA — concentration of water vapor C*A — dimensionless concentration of water vapor DAR — binary mass diffusion coefficient, m2/s D,, = hydraulic diameter, m hmx = local convection mass transfer coefficient, m/s /zv = local convection heat transfer coefficient, W/m2-K

Holographic interferometry using two-wavelength holography for the measurement of large deformations

Visible holographic interferometry is generally too sensitive for the measurement of large deformations. We present a holographic method that permits an increase in the range of measurable deformations. It requires the use of two different wavelengths, λ(1) and λ(2), and two holograms in series. We develop the theoretical basis of a method that permits the obtention of an interferogram as if a longer equivalent wavelength, λ(eq) = λ(1)λ(2)/|λ(1) -λ(2)|, were used. The method is experimentally tested by use of a setup that can be easily converted into a classical single-wavelength holographic interferometer, permitting comparison of the interferograms of the same deformation produced with both methods. Significant results are presented.

Holographic studies of the bubble generated by a seismic airgun

Using a Nd:YAG laser in single and double pulse mode, the dynamic behavior of bubbles generated by a small airgun, placed in a water tank, has been investigated. Single pulse holograms of the bubble have been obtained with the purpose of investigating the shape and smoothness of the surface. Interferometric holography, or double pulse holography, of the bubble has been performed in order to detect the pressure wave from the gun at the early stages of the bubble expansion. The optical phase delay of the laser beams traversing the test section is caused by a local change in the refractive index of the water in the tank due to the acoustic disturbance. A theory for relating the change of the refractive index to bubble parameters is presented. Modeling of interferometric holograms has been performed with the aim of qualitatively comparing them with the recorded holograms. From the holograms it is observed that the surface of the bubble is relatively smooth during the first expansion. During the contraction, and the following oscillations, the bubble surface becomes highly nonsmooth and chaotic due to the developed turbulence in the surrounding water.

Shock Wave Reflection and Focusing over Circular Concave Walls.

A planar shock wave reflecting from a circular concave wall generates a local pressure/temperature amplification at a certain point adjacent to the center of the concave wall. This phenomenon is, so-called, shock wave focusing but, in this case, it is caused by the collision of a pair of triple points formed on the shock reflection process. This mechanism is considered to be governed by the behavior of these triple points and depends on the shape of reflector. In this paper, in order to clarify the contribution of the triple points and its three-shock structure to the focusing mechanism, the difference of an initial angle of concave wall as a shape of reflector was discussed. Particularly, the behavior of a secondary triple point and its slip line behind a normal shock which was formed due to the inverse Mach reflection was investigated by using double exposure holographic interferometer. Numerical simulation was also carried out using Harten-Yee type second order upwind TVD finite difference scheme applied to 2-D Euler equations. The numerical results are compared with the interferograms.

レーザーホログラフィー干渉計の低温熱流体現象への応用

A laser holographic interferometer was successfully applied to the visualization of the phenomena in cryogenic liquids, in particular the visualization of natural convection in liquid nitrogen and of thermal and pressure wave propagations, transient boiling and transient evaporation from a free surface in superfluid helium (He II). This technique has the advantage in yielding straightforward quantitative data. Counting interference fringes which appear in a holographic image provides quantitative information on the temperature or pressure variation in the liquid of interest. This method was also found to be applicable to even a very small variation of temperature, especially in thermal shock waves.

Interferometer based on the Talbot effect in holography

This paper discloses an interferometer based on the Talbot effect in holography and combining in itself properties of the Talbot and of the holographic interferometers. The second grating is replaced with the hologram of the first grating in the interferometer proposed, which constitutes its difference from the Talbot interferometer and which results in an interferometer having four output informational channels with different sensitivities.