Laser Interferometry Method Research Articles

ヘテロダイン干渉法による動的変位計測のディジタル化

The dynamic measurement of nanometer-order displacements was realized by using our heterodyne laser interferometry method. The measuring system of the existing method contains two analog devices, namely, a frequency divider and a phase meter, and various electrical and electronic noises are apt to be picked up by them. In addition the frequency divider has a minimum limit of 1/32 and troublesome manual operation is needed in the range exchange. To avoid the above inconveniences, we replaced the analog devices with a digital method using a special software package. The improvement was successful and the measurable frequency range was expanded to 300 Hz and above.

Seismoacoustic Hydrophysical Complex for Monitoring the Atmosphere–Hydrosphere–Lithosphere System

The seismoacoustic hydrophysical complex intended for investigation of the interaction of geospheres wave fields in a frequency range from 1 μHz to 1 Hz is described. The complex consists of a shore-based system of laser strain meters, laser nanobarograph, bottom station with a hydrophone and a temperature-sensitive element, weather station, and seismoacoustic radiator. The use of modern laser-interferometry methods provided a deformation sensitivity of ∼10–10 and an atmospheric-pressure sensitivity of 10 mPa.

Design of Composite Surrogate Mirror Support Structure

Three multimaterial support structures were designed and built to support 200 mm (8 in.) diameter “surrogate” mirrors for the deployable optical telescope (DOT) ground experiment at the Air Force Research Laboratory (AFRL/VS). A “spider-truss” structure was selected for its stiffness. Materials used included “Invar” alloy and AS4-epoxy composite rods manufactured by the “pultrusion” process, for their low thermal expansion coefficients, and aluminum for its machinability and low density. The composite rods were pultruded at AFRL/VS, and their coefficients of thermal expansion (CTE) were determined by a laser interferometry method. Finite-element method (FEM) analysis of the vibration modes of the structure was conducted to determine the optimum selection of materials. FEM analyses were also used to determine the mirror surface figure errors caused by ±5°C temperature fluctuation, as a function of the materials chosen. The paper discusses the rationale for the materials selection and design issues.

On the jump-like creep of cross-linked polymers and composites based on them

The study on the jump-like character of creep of differing in their morphology polymers was continued. The creep processes were recorded using the method of laser interferometry, allowing investigations on strain rate inhomogeneity on micron level and determination of strain jump parameters. Polyester resins and filled composites based on them were used as objects of the investigation. It is shown that the characteristics of jump-like creep change considerably depending on material composition and strain stage. It is assumed that the strain jumps on micron level reflect the presence of ordered formations of the same scale in the structure, as well as their transformations.

Determination of the piezoelectric coefficients d of PZT ceramics and composites by laser interferometry

We have measured the piezoelectric coefficients of PZT ceramics by resonance and laser interferometry methods. The surface displacement was measured by a single-beam Michelson interferometer. A stable double-beam interferometer was also used to suppress the effect of bending. The piezoelectric coefficients dij of the PZT ceramic and of the 0–3 ceramic–polymer composites were determined from the displacements. The results for PZT dij coefficients obtained by the both methods are in good agreement.

The electronic laser interferometry and laser heating method for residual stress determination

Residual stress is one of the causes which makes defects in engineering components and materials. These residual stresses can occur in many engineering structures and can sometimes lead to premature failures. There are commonly used methods by which residual stresses are currently measured. But these methods have a little damage and other problems; therefore, a new experimental technique has been devised to measure residual stress in materials with a combination of electronic laser interferometry, laser heating and finite element method. The electronic laser interferometer measures in-plane deformations while the laser heating and cooling provides for very localized stress relief. FEM is used for determining the heat temperature and other parameters. The residual stresses are determined by the amount of strain that is measured subsequent to the heat-up and cool-down of the region being interrogated. A simple model is presented to provide a description of the method. In this paper, the ambiguity problem for the fringe patterns has solved by a phase shifting method.

Concentration polarization of ion-exchange membranes in electrodialysis: An interferometric study

The three-frequency laser interferometry method is used for studying the concentration polarization of ion-exchange membranes in a wide range of current densities. The concentration and temperature fields of solutions involved in electrodialysis of sodium chloride are measured simultaneously. The proposed method makes it possible to measure absolute values of local concentrations of acids and bases that form during irreversible dissociation of water molecules at the solution-membrane interfaces following an increase in the current density above the limiting value. According to an analysis of the concentration and temperature distributions in an electrodialyzer channel, maximum variations in the measured quantities occur near the interface. Dependences of the near-membrane concentrations and temperatures on the current density are compared with the voltammogram. The comparison shows that reaching the limiting current density sharply accelerates the nonequilibrium dissociation of water molecules and increases the temperature

Differential laser-interferometer for thermal expansion measurements

The differential laser interferometry method and its application for measuring the thermal expansion of samples is described. The thermal expansion of single-crystal Al2O3 (corundum) was measured up to 1000 K with the differential laser-interferometer. The changes in the distance between two faces of a stepped shape sample are measured. The main feature of the apparatus is simultaneously monitoring two fringe signals that are 90° out of phase. This improvement of the basic laser-interferometer allows us to remotely measure the thermal expansion of minerals with high precision. The overall sensitivity with which we can detect changes in length is about 1/100 of the wavelength of the He-Ne laser (1/100 of 0.6328 × 10−6 m). After adjusting for errors caused by heat, the thermal expansion data measured with the differential laser-interferometer are in good agreement with previous reports. Use of this apparatus allows the investigation of the high-temperature thermodynamic properties of important rock-forming minerals.

Laser-interferometry study of the barrier effect in the electrodialysis of amino acid solutions

Electrical mass transfer of amino acids through ion-exchange membranes is modeled experimentally by the laser-interferometry method. A direct proof is obtained for the barrier effect in electrodialysis of solutions of amino acids at current densities exceeding the limiting value.

Determination of the mass of an imploding gas puff

A method for determination of the mass of an imploding gas puff with the use of piezoelectric gages has been proposed and tested. The data obtained in this experiment are compared with those obtained by the method of laser interferometry of gas. The measurement results of both experimental sets are in good agreement within the operating range of delays between the opening of the gas valve and the operation of the current generator.

Diagnostics and analysis of incident and vapor shield plasmas in PLADIS I, a coaxial deflagration gun for tokamak disruption simulation

Tokamak disruption simulation experiments have been conducted at the University of New Mexico using the PLADIS I plasma gun system. Earlier work had characterized the plasma-surface interaction in terms of parameters such as incident energy from bucket calorimeter measurements and rough measurements of beam area from flat damage targets. A variety of new plasma diagnostics have been used to further investigate the characteristics of the incident plasma beam and vapor shield plasma in a simulated tokamak disruption. These diagnostics have included laser interferometry, two-color pyrometry, emission spectroscopy, and other methods to quantify the characteristics of the incident and vapor shield plasmas of a simulated tokamak disruption. The synthesis of different beam area measurement techniques is used to determine the radial structure of the plasma beam. Vacuum ultra violet spectroscopy is used to determine the thickness and internal structure of the vapor shield plasma. Results from two-color optical pyrometry and surface pressure measurements are used to determine the dynamics of vapor shield formation.

Quantitative flaw reconstruction from ultrasonic surface wave fields measured by laser interferometry

A quantitative imaging method for ultrasonic nondestructive testing of structures is presented. The method employs two-dimensional surface-vibration data that is obtained by laser interferometry methods such as holography and digital phase-stepping shearography. In this method, a surface wave field generated by a narrow-band contacting or noncontacting ultrasonic transducer is Fourier transformed to obtain a spatial-frequency domain representation of the wave field. The appropriate Green’s function is then deconvolved from the wave field to obtain quantitative images of effective scattering sources. Since scattering strength is directly proportional to the local contrast of the structure, these images provide a direct map of internal flaws in structures such as plates and shells. The method is valid for strongly scattering inhomogeneities, and can employ scattered evanescent waves to obtain resolution of flaws much smaller than a wavelength. Simulated and experimental results illustrate the efficacy and quality of the imaging method.

Experimental Study on Heat Flux from an Argon RF Plasma Using Laser Interferometry Method

The plasma heat flow to a birefringent substrate (LiNbO3) in an argon rf discharge has been investigated with the help of a laser interferometry method. This method is based on monitoring the variation of natural birefringence with temperature by the interferometry. The evaluation of the temperature curve shows that heat flux from the plasma towards the substrate depends on which electrode the substrate is put on. While the value is about 8% of the applied power in the case of the substrate on the powered electrode, the heat flux decreases to less than 1% in the case of on the grounded electrode. Ion fluxes have been obtained from the measured values of plasma potential, electron density and electron temperature. In the case of low pressure the ion flux approximately agrees with the value of the heat flux. However it decreases with an increase in pressure, and is almost 35% of the heat flux at 200 mTorr. Gas temperature in the plasma has been measured using a thermocouple in order to investigate the influence of gas pressure on the heat flux by neutral particles. The result shows that the gas temperature increases by raising the gas pressure.

Continuous monitoring of acid stratification during charge/discharge by holographic laser interferometry

The change in the acid concentration in the vertical direction in a lead/acid battery is monitored continuously during charge/discharge cycling by means of a holographic laser interferometry method. It is found that there is a difference in the acid distribution in the upper and lower parts of the electrolyte due to uneven reaction speeds and acid movement by natural convection. This causes an interesting re-emergence of an uneven distribution during the interval between charge and discharge.

Concentration fields of solutions under electrodialysis with ion-exchange membranes

The laser-interferometric method for measuring concentration profiles in compartments of electrodialyzers with a small intermembrane distance is developed using an optical cell with a moveable membrane. The method of laser interferometry is used for determining of the limiting diffusion current density by the minimal interface concentration of the solution. The method of a local distributive analysis of diffusion boundary layers of two-component solutions by two-frequency laser interferometry is proposed and the distribution of concentrations in the sodium chloride-calcium chloride system is investigated.

Electrodynamic reciprocity method for vibration standards

In a previous paper, a reciprocity calibration formula different from the Levy–Bouche’s is derived [L.-F. Ge, Proceedings of the XIII IMEKO World Congress, 2606–2610 (1994)]; the latter has been regarded as a standard method [ISO 5347-0, 1987; ISO/DIS 5347-20, 1990]. The new formula is S=(RT/jω)1/2 (V/ms−2), where T is the mean of the transfer admittance ratio, Tn=Mn/(Yn−Yo) and R is the voltage ratio for the typical three-transducer-two-experiment procedure, in which an electrodynamic transducer serves as reciprocal one. This method is suited to the low- and mid-frequency ranges, and most accurate at 100–1000 Hz. This paper reveals that a coefficient of variation, i.e., ratio of standard deviation of Tn to its mean value, can be viewed as a reciprocity index of such an electrodynamic calibration system including two transducers and a solid mass medium. An index smaller than 0.5% indicates that the system is better reciprocal, and can be calibrated more accurately. At frequencies higher than about 3000 Hz, nonlinear problems, such as stress wave effect and resonance, become pronounced, and should be considered; a better way would be to apply other more available methods, such as the laser interferometry and piezoelectric reciprocity method.

Study of the dimensional stability of a carbon-fiber-reinforced plastic by the method of laser interferometry

1. The method of laser interferometry is the most sensitive, precise, and reliable method for measuring microscopic changes in the geometric dimensions of specimens of carbon-plastic, since the measurements are scaled to a natural length — fractions of the wavelength of the laser radiation. 2. The drift of the geometric dimensions of "dry" and "moist" specimens of carbon-plastic under natural conditions occurs during the first several hours. The sign of the drift differs on different specimens: dry specimens are saturated by moisture and the linear dimensions increase; drying takes place in the case of the moist specimens, i.e. the linear dimensions decrease (see Fig. 3). 3. Preliminary thermocycling stabilizes the geometric dimensions of carbon-plastics and improves their dimensional stability. The moistening-drying cycle does not increase the dimensional stability of the composite. 4. The location of the reinforcing fibers in the surface layers affects the dimensional stability of a carbon-plastic only in the case of dry specimens. Less drift occurs in specimens in which the fibers are longitudinally oriented. 5. Specimens that are stored for a long time and then chemically dried to a constant mass have the same dimensional stability as freshly prepared thermocycled specimens (curves 2–4 and 7, 8 in Fig. 3).

Experimental study of fracture processes in rock

The Fracture process zone in compact tension specimens of Indiana limestone was investigated to study its effect on the fracture mechanics parameters in such materials. Specimens were tested up to the peak load, and propagation of the crack from a preexisting notch was monitored. Experiments were designed to study the two features of the fracture process zone in rocks: ligament connections and microcracking. To observe this zone with high sensitivity and accuracy, laser interferometry methods were adopted. Holographic Interferometry was used to observe initial crack propagation. To obtain more quantitative measurements of the displacement field, in realtime, the recently developed technique of electronic speckle pattern interferometry was applied. This technique can provide continuous video recording of the interferometric fringe pattern, depict the evolution of the fracture process, and measure profiles of crack opening displacements. The macroscopic observations of full-field displacement by the laser techniques were supplemented by post mortem observation of the fracture region under a scanning electron microscope. Regions around the crack were studied after the test for possible presence of microcracks. An interactive finite element code was used to compute the stress intensity factors of the propagating crack-tip and displacements. Finite element computations were used to evaluate the effect of the process zone on crack propagation.

Determination of internal mechanical stresses in coatings by a laser interferometry method

Determination of internal mechanical stresses in coatings by a laser interferometry method

Determination of the amplitudes of mechanical stresses and displacements in short cylindrical piezoelectric transducers with passive layers

The distribution of dynamic mechanical stresses and displacements in piezoelectrical transducers with a transition layer, made in the form of hollow cylinders whose length is commensurable with the radius, is considered. Expressions for the mechanical stresses and displacements in relation to the voltage are obtained by solving the boundary-value problem of forced transducer vibrations. This axisymmetric problem is stated under the assumption that the hypothesis of plane sections holds. It is found that the greatest dynamic tensile stress acts on the transition layer and that the strength of cylindrical transducers with a transition layer is primarily determined by the strength characteristics of the material of which the transition layer is made. The theoretical results are supported by experiments performed according to the laser interferometry method.