Holographic Interferograms Research Articles

Visualization of 3D gas density distribution using optical tomography

This paper presents a visualization of a 3D gas density distribution, which arose from a safety analysis of a high-temperature gas cooler reactor. The density distribution is reconstructed from holographic interferograms using the techniques of computed tomography. In the reconstruction process, a new reduced bandlimit technique is used in the filtered-backprojection algorithm to deal with the truncated projection data with noise. The results reconstructed from 12 view directions are verified qualitatively by an oxygen molarity detector. It shows that the filtered-backprojection algorithm, integrated with the reduced bandlimit technique, can reconstruct the 3D density distribution from the truncated and noisy projections, and that holographic interferometry is a non-disturbing and powerful tool in flow-visualization for 3D gas flows.

Monitoring and measuring electrochemical behavior of engineering alloys by optical interferometry

In a previous study, an optical corrosion meter was built based on a mathematical model relating to surface and bulk behaviors of metals in aqueous solution. The optical corrosion meter was established based on principles of holographic interferometry for measuring microsurface dissolution, i.e., mass loss, and on those of electrochemistry for measuring the bulk electronic current, i.e., corrosion current. The corrosion meter consists of an electrochemical cell in which the sample is immersed in aqueous solution. Furthermore, the corrosion meter has a holographic camera with a thermoplastic film for in situ processing holograms in order to obtain real-time holographic interferograms of the sample in the electrochemical cell. Results of the present work indicate that optical holography is a very useful technique for measuring the corrosion current density of different alloys in aqueous solutions. As a result, the corrosion current density of aluminium, stainless steel, low carbon steel, copper, and brass in 1M KCl, 1 M NaCl, 1 M NaOH, seawater and seawater solutions, respectively, were obtained. The obtained corrosion data from the optical corrosion meter (interferometric technique) were compared with corrosion data obtained on the same alloys in the specified solutions from the linear polarization method as well as from the weight-loss method. The comparison among the three techniques indicates that there is contrast in the results among the investigated alloys. In general, the new method of optical interferometry can be considered a more conservative method of corrosion measurement with respect to the linear polarization and weight-loss methods.

Vortex ring, shock-vortex interaction, and morphological transformation behind a finite cone

Axisymmetric compressible flow field induced by shock diffraction from a finite cone is investigated with experimental and computational methods. Double-exposure holographic interferograms show images of the density field integrated along the light path. Using the sight-integrated density based on the Able transformation, the axisymmetric computational results are compared qualitatively with the experiment. In the present paper, we observed some distinguishing flow physics: the fault structure of vortex ring, the shock-vortex interaction, and the morphological transformation of shock waves.

Fringe skeletonizing using an improved derivative sign binary method

A modified derivative sign binary method is proposed to extract fringe skeletons from interferometric fringe patterns. A fringe direction map ranging from 0° to 360° is obtained with an unambiguous relationship between the grayscale and fringe tangent direction. Using this approach, the derivative sign binary map is detected without a fringe direction jump. The dark (light) fringe intensity minimum (maximum) can be extracted automatically to define fringe skeletons. In addition, two different anisotropic one-dimensional filters are described that can be used for further improving the fringe quality. Examples are provided for a holographic interferogram and a Moiré fringe pattern to illustrate applications and benefits of the approach.

Some investigations in holographic microscopic interferometry with respect to the estimation of stress and strain in micro-opto-electro-mechanical systems (MOEMS)

Holographic microscopy with conjugate reconstruction for the interferometric determination of three-dimensional displacement was used for the investigation of the mechanical behaviour of micromechanic and microelectronic components. An experimental set-up for the exposure of the holographic interferograms is described for the application of the spatial heterodyne technique, for the application of phase shifting, and for electro-optic holography. Three holograms for different illumination directions recorded on one holographic plate were reconstructed conjugately, and spatial-heterodyne technique as well as phase-shift technique were used to evaluate the interferograms. Only by conjugated reconstruction, it is possible to obtain a perfectly optimised interferometer for the static evaluation method. The evaluation of interferograms, which are strongly disturbed by speckle noise, can be performed successfully. A comparison of the results of the application of these techniques is given. The influence of the speckle effect on the resolution was investigated.

Shock wave interaction with a spiral vortex

Previous studies on shock–vortex interactions have either been numerical in nature with idealized boundary conditions and prescribed vortex flows, or in complex experimental flow fields, such as where the vortex is shed at the trailing edge of an aerofoil. In this study a bifurcated shock tube facility has been constructed where two plane waves arrive sequentially at the trailing edge of a wedge. The first shock wave results in a spiral vortex being shed, which is then impacted by the second wave. Accurate control of the delay between the two shock waves was achieved using a highly repeatable piston actuated shock tube driver. A number of interesting new features of this interaction have been identified. The work specifically examines the development of a transient pressure spike, physically occupying an area less than 0.5 mm in diameter and having a duration of 15 μs, with a pressure nearly two-and-a-half times that of the surrounding fluid. This has been done both numerically using an adapting mesh Euler code, and experimentally, the latter with the careful use of fast response miniature pressure transducers. Numerically generated holographic interferograms and shadowgraph images have been generated for direct visual comparisons with the equivalent experimental results of the whole flow field, from which the reason for the production of the pressure spike is established as being due to local shock wave focusing resulting from part of the shock being pulled around the vortex to impact on itself. The generation of a second pressure peak is also examined, as is the wave field emanating from the interaction and the influence on the vortex. The use of both experimental images and numerical flow visualization algorithms were found to provide complimentary information, which allowed for detailed investigation and understanding of the shock wave–vortex interaction.

Effect of Interference-Fringe Noises in Numerical Analysis of Sinusoidally Phase-Modulated Holographic Interferograms: Theoretical Investigation

In this paper, we present a numerical analysis of the effect of random noises contained in interferograms of a vibrating object. We theoretically investigated the case where several Bessel-function arguments are used to determine object-vibration phasors. The value of each argument can be calculated from holographic interferograms with phase-modulation phasors of the same magnitude but of different phases. The root-mean-square (rms) error values of object-vibration amplitudes are different for the two algorithms, called synchronous and sum algorithms. At smaller object-vibration amplitudes, values determined by the former have higher accuracies, while for larger amplitudes, those determined by the latter have higher accuracies. Averaging these values by weights, which are the square reciprocals of the respective rms errors gives higher accuracies. The rms error values depend on the phase-modulation magnitude. These values in the cases of the former and latter algorithms are minimum at phase-modulation magnitudes of 0.640π and 0, respectively.

Holographic Interferometry Using a Double-Pulse Ruby Laser with Nonsimultaneous Flashes of Pump Lamps

A method for extending the interval between paired laser pulses is investigated. This method is based on pumping an active medium by two groups of flash lamps with nonsimultaneous discharges, each of which excites a giant pulse. It is established that, at asymmetric pumping with respect to the cavity axis, a difference in the pulse propagation paths is achieved because of the thermooptic distortions of ruby rods, which result in the impossibility of recording holographic interferograms for a pulse separation exceeding several milliseconds. An unlimited interval between pulses is achieved when using a four-lamp laser pump chamber ensuring axially symmetric pumping.

Visualization of shock-vortex interaction radiating acoustic waves

Unsteady compressible flow fields past a wedge and a cone, evolved by propagation and interaction of shock waves, slip lines, and vortices, are studied by shadowgraphs and holographic interferograms taken during the shock tube experiment. The supplementary numerical calculation also presented time-accurate solution of the shock wave physics which was essential to recognize the similarity and dissimilarity between the wedge and the conical flows. The decelerated shock detained by the vortex interacts with the small vortexlets along the slip layer, producing diverging acoustics: this phenomenon is more distinct in the case of wedge flow for a given shock Mach number. The decelerated shock penetrated through the vortex core constitutes a transmitted shock, which eventually merges with the diaphragm shock that bridges the vortex pair/vortex ring. This phenomenon became remarkably salient in the case of conical flow.

Specific features of partially coherent holography of dynamic objects

A method for recording partially coherent holographic interferograms is proposed, which makes it possible to control the sensitivity to the object point displacement by instrumental means. In this case, a decrease in sensitivity is accompanied by a decrease in the depth of the reconstructed image, which simplifies automated inputting of the resulting interferogram into a computer for further processing. The calculations showed that the partially coherent holograms using transverse scale transformation in one of the arms of a recording interferometer with a scale factor different from −1 possess the interferometric sensitivity, whereas the partially coherent holograms with the wave-front rotation in one of the arms of a recording interferometer lack the interferometric sensitivity to the displacement of object points during recording. The latter feature allows us to record objects whose displacement considerably exceeds the wavelength of recording radiation.

Holographic analysis of musical instruments

Musical instruments, when excited by bowing, plucking, blowing, or striking, vibrate in rather complicated ways. These complicated vibrations can be described in terms of normal modes of vibration, and understanding the normal modes or eigenmodes is important to understanding sound production in the instrument. Holographic interferometry offers by far the best spatial resolution of operating deflection shapes (and hence of normal modes), since it looks at an almost infinite number of points. Holographic interferograms may be recorded on photographic film or electronically by means of TV holography. We discuss various methods for holographic interferometry and its applications to several different types of musical instruments.

Formation of holographic shearing interferograms for wave-front monitoring

Formation of holographic shearing interferograms for wave-front monitoring

Spatial Filtering of Holographic Interferograms of Lateral Shear for Wave-Front Control

Conditions for lateral shear interferogram formation in fringes of infinite width to control converging wavefronts for a double-exposure recording of Fresnel holograms of a mat screen are analyzed for the case of spatial filtering of a diffraction field in the record reproduction stage. The interferometer sensitivity is shown to be limited due to reference wave aberrations during double-exposure hologram recording, when a photoplate is displaced before the second exposure.

Vibration mode separation of transient phenomena using multi-pulse digital holography

A rectangular flat metal plate is made to randomly vibrate when excited by a shaker. A digital holographic interferometry out-of- plane optical system is used to investigate the temporal development of the induced transient deformations. The system relies on two and four laser pulses emitted within a single envelope of the flashlamp contained in the oscillator cavity of a ruby laser, and also on three CCD cameras used to record two or four digital images resulting from the same number of holographic interferograms. Hologram data reconstruction is per- formed digitally and Fourier evaluated to obtain quantitative deformation data for each of the formed interferograms. The deformation data is bro- ken down into resonant mode components, sums of which are used to computer reconstruct the experimental deformation data. The error pro- duced when using a finite sum of resonant mode components is consid- ered. Experimental and computer reconstruction results for the transient vibration deformation of the plate are presented and compared. © 1999 Society of Photo-Optical Instrumentation Engineers. (S0091-3286(99)01712-2)

Acoustics of ancient Chinese bells

Many ancient Chinese bells, some more than 3000 years old, remain from the time of the Shang and Zhou dynasties. Most of these bells, being oval or almond shaped, sound two distinctly different musical tones, depending upon where they are struck. Studies of these bells have provided us with much knowledge about the musical culture of Bronze age China. Results are reported from our investigations of original bells in the Shanghai Museum and the Sackler Gallery at the Smithsonian Institution, as well as replica bells in our own laboratory. Modes of vibration in original bells, obtained by experimental modal testing in the museum, compare very well with holographic interferograms of replica bells. Our results are compared with our catalogue of data on ancient Chinese bells gathered by other investigators. Although acoustical studies have revealed a great deal about ancient Chinese music and casting practices, several questions still remain unanswered.

In vitro testing of bioprostheses: influence of mechanical stresses and lipids on calcification

Background. Structural valve deterioration of bioprostheses is mainly caused by the progressive development of calcification. Mechanical stresses or lipid deposits in porcine aortic leaflets have been proposed as major factors contributing to the calcification process. Methods. A new test protocol consisting of nondestructive holographic interferometry, which allows a quantitative deformation analysis of heart valves, and accelerated dynamic in vitro calcification was used. The rapid calcification fluid contained a final combined calcium and phosphorus concentration of 130 (mg/dL) 2 in barbital buffer solution. The calcification of 32 bioprostheses donated by different manufacturers (SJM Bioimplant, Biocor standard, Biocor No-React, Carpentier-Edwards SAV, Bravo, pericardial prototype) was assessed after up to 25 × 10 6 cycles by microradiography and the areas of calcification were compared with the holographic interferograms. The distribution of lipid droplets of four porcine prostheses were visualized by Sudan III stain before the calcification process. Results. Most of the tested bioprostheses had areas presenting with stress concentrations, and the dynamic in vitro testing resulted in leaflet calcification corresponding to the holographic irregularities. A strong correlation between calcification and stress distribution or lipid accumulation was found ( r = 0.72; r = 0.81, respectively). After 19 × 10 6 cycles, the Carpentier-Edwards SAV and the pericardial valves had significantly less calcification than other prostheses tested ( p = 0.003), but the variation among individual prostheses from the same manufacturer was even more pronounced. Conclusions. Mechanical stresses or lipid accumulation seems to play an important role in the calcification process of bioprostheses. Quality control of bioprosthetic valves using holographic interferometry has the potential to predict calcification before implantation.

Problems of interpretation of holographic interferograms near shock wave fronts

A method of avoiding ambiguity in the interpretation of interferograms near a shock wave front is proposed. The method is based on combining the double-exposure schlieren method and holographic interferometry. Relations for calculating, on the basis of data obtained by analyzing double-exposure schlieren photographs, both the density at the shock wave front and the gradient of the density directly behind the front, which is necessary for calculating the shifts of the interference fringes near the shock wave front, are presented.

Observations of the plasma dynamics of a vacuum spark from its soft x-ray emission

Experimental observations of the plasma dynamics in a vacuum spark are presented which permit measurements of the electron density and temperature during a large part of the compression phase of the pinch. The vacuum spark is generated by a low-impedance pulse forming line with a maximum current in excess of 100 kA. The discharge is operated in the hybrid mode in a titanium plasma. A laser focused onto the cathode provides the preionizing source. Soft x-ray emission from the current sheath is observed with an x-ray framing camera well before maximum compression. These observations are compared with holographic interferograms, both showing the formation of an axisymmetric rhombic boundary to the plasma sheath. The temperature and density of both the sheath and the internal plasma are observed until the formation of hot spots at the time of maximum compression. The temperature evolution of the hot spots is presented, showing a repeatable behavior that depends on the axial position.

Some characteristics of relief formation on photothermoplastic carriers used in double-exposure interferometry

An analysis is made of the main trends in the development of a surface relief on photothermoplastic carriers of optical information used to record double-exposure holographic interferograms. It is shown that high-quality interferograms require recording conditions (taking into account the composition of the material and the heating temperature of the thermoplastic carrier layer, as well as the parameters of the sensitizing corona discharge) where the surface of the photothermoplastic carrier can be treated in the equipotential approximation.

Interferometry of phase micro-inhomogeneities within macroscopic objects

A procedure by which simultaneous large- and small-scale inhomogeneities of the refractive index of an object can be assessed is presented. The information is obtained from a hologram and a simultaneous double-exposure holographic interferogram. The small-scale information is obtained by looking under magnification at the interference pattern which forms the actual hologram. This is complemented by observation of the image reconstructed from the same hologram. The large-scale information is obtained from the double-exposure holographic interferogram. The procedure was experimentally tested using a hand-drawn quartz fibre of in diameter. A straightforward application is shown in which the object under study is a laser-produced spark in air. Early on, small-scale structures are present in this type of micro-plasma. The method can be directly applied to obtain the density profiles of hot-spots developed in a transient plasma discharge. Other possible applications are suggested.