Optical Interferometric Method Research Articles

Electric Current Measurement with Enhanced Sensitivity Using two Metal-coated Fibres

Abstract An optical interferometric method using two metal-coated single-mode fibres is proposed for d.c. electric current measurement. Experimental results prove that the sensitivity of measurement can be well enhanced by the new method.

Electrokinetic properties of metal-dielectric interfaces

Using an optical interferometric method capable of determining mechanical displacements in the nm to pm range, measurements are reported of displacements resulting from electrically induced strains in a variety of metal-dielectric interfaces. The dielectrics include aqueous electrolytes, glycol, glycerol, silicone oil and polyethylene. The displacements are shown to conform to the predictions of the Lippmann equation. The implications of these measurements are discussed and are believed to be particularly important in the initiation of failure in polymeric insulation at high voltage. The results also suggest possible device applications based on the electromechanical, piezoelectric properties of these interfaces.

Phase Measurement by Differentiating Interferometric Fringes

Abstract In this paper we discuss a method of wavefront phase detection by differentiation of the interferometric fringes. We show that only one phase step is required to determine the wavefront phase. In the process of differentiation, Moiré fringes are formed. Conditions on the angle of tilt introduced between the interfering beams to overcome the formation of Moiré fringes are also presented. The method is shown to be suitable for techniques such as null optical testing or interferometric methods where comparison is made between a master and a test. We present in this paper the theory of the method and experimental results obtained for both specular and speckle interferometric fringes.

Acousto-optics in Poland

Polish achievements in acousto-optics are reviewed, including optical holographic interferometric methods for ultrasonic fields and vibrating transducer examination, ultrasonic light diffraction phenomena and their modulation problems, material examination of anisotropic liquids and solids, and construction of acousto-optical devices. Topics reflect research being conducted in university centers in Gdansk, Gliwice, Poznan, and Warsaw. The studies are described and illustrated by means of arbitrarily chosen examples. Over one hundred references are cited.

A high-accuracy dilatometer for the range ?20 to 700�C

We have constructed a linear-thermal expansion apparatus that employs a potassium-loaded heat pipe to provide a homogeneous temperature environment for the sample and utilizes the Merritt-Saunders (optical interferometric) method of observing its expansion. The apparatus is similar in many respects to one described previously. Temperature regulation and measurement are accomplished through the use of a dedicated laboratory microcomputer operating with a simple program. Two platinum resistance thermometers, read automatically by a digital resistance bridge, provide, on command, both the temperature of the heat pipe and that of the sample chamber. Changes in sample length are determined from measurements of the corresponding changes of optical fringes from a Fizeau interferometer as recorded on film. The coefficients of thermal expansion of two Pt-Rh alloy samples determined using the present apparatus agree at the±2 ppm level with those determined for a similar sample using the previous apparatus.

Time-resolved electron density measurements in an ArF excimer laser discharge

The electron density in an ArF excimer laser discharge has been measured by means of a time-resolved optical interferometric method. By comparing the behavior of electron density in the absence of F 2 gas with that in the presence of F 2 gas, the dissociative attachment rate is estimated from graphical calculation.

Pressure-dependent transient behaviour of the population of atomic and molecular metastables in He discharge

The transient behaviour of the population of excited state helium atoms (2 3S 1, 2 1S 0, 2 3P) and molecules (2sσ 3Σ + u) under a fast pulsed discharge excitation in pure helium has been studied experimentally using the optical interferometric method and the absorption method with nanosecond time-resolution. Experimental results are presented of the time dependent behaviour of these populations in the afterglow over a wide range of gas pressure from 35 Torr to 3 atm.

Photodisplacement imaging—A static regime

An optical interferometric method has been used to measure the static surface deformations caused by a point-focused cw laser. Experiments carried out in Plexiglass show that one can guess for defects or inhomogeneities under the surface through the topography of these deformations.

Optical observations of unidirectional solidification in microgravity

Optical interferometric, shadowgraph, and streak photographic methods are used to obtain temperature profiles, concentration gradients, and fluid velocities in NH4Cl-H2O metal-model solution during unidirectional solidification in microgravity. This study elucidates earlier low gravity suborbital rocket experiments and lays the groundwork for space shuttle experiments. The design and operation of the optical units are presented, and results are detailed to ground based experiments. The low gravity experiments were conducted using a KC-135 aircraft flying a parabolic trajectory.

Piezoelectric Relaxation in Ferroelectric AgNa(NO2)2

The complex piezoelectric constants, d 21 , d 22 and d 23 , of ferroelectric AgNa(NO 2 ) 2 have been measured by two quasi-static methods; one is the optical interferometric method and the other is based on a comparison with the piezo-electric constant of quartz. The measurement covered the temperature range from 40°C to -80°C and the frequency range from 5 Hz to 50 kHz. All d 2 j 's show dispersion of the Debye type, d 2 j (ω)= d 2 j (∞)+[ d 2 j (0)- d 2 j (∞)]/(1+ i ωτ). The relaxation time, τ, which is of the order of 5 ×10 -6 sec at room temperature coincides with the dielectric relaxation time and shows critical slowing down toward T c (37°C). It has been found that the dipolar contribution, [ d 2 j (0)- d 2 j (∞)], and the ionic and electronic contribution, d 2 j (∞), are of opposite signs to one another and the static piezoelectric constant, d 2 j (0), changes its sign at some temperature in the ferroelectric phase.

Optical interferometric measurement of the thermal expansion of NdP5O14

The anisotropic thermal expansion coefficients of NdP5O14, a stoichiometric laser material, have been measured by an optical interferometric method. The expansion coefficients are αa = (10.0±1.3)×10−6,αb = (9.5±1.1)×10−6, and αc = (8.3±1.0)×10−6.

Diffusion Coefficients of Rb+ and Cs+ Ions in Molten Nitrate Systems

Abstract The tracer diffusion coefficients of 86Rb and 137Cs ions in the molten (Li-Na)NO3, (Li-K)NO3, (Li-Rb)NO3, and (Li-Cs)NO3 systems have been measured by means of a paper strip method. Results from the paper strip method in some pure nitrates are compared with the results from capillary and optical interferometric methods. With increasing concentration of LiNO3, the diffusion coefficients at 350°C are found to decrease in the (Li-Na)NO3 system and to increase in the (Li-K)NO3, (Li-Rb)NO3, and (Li-Cs)NO3 systems. For 86 Rb in (Li-K)NO3 an increase is followed by a decrease. These findings are discussed by taking into consideration the free space in the solvent system and the ionic interaction between the diffusing and the surrounding ions.

Piezo- and elasto-optic properties of deuterium oxide under high pressure

The variation of the refractive index of D20 with pressure has been determined using g the high precision optical interferometric method.(AIP)

Methods for the analysis of ternary free-diffusion processes by the Rayleigh optical interferometric method

Equations are presented for the analysis of ternary free-diffusion processes in liquid systems by the Rayleigh optical interferometric method. Four different analytical derivations are given and two numerical methods of analysis are discussed.

Piezo- and elasto-optic properties of liquids under high pressure. I. Refractive index vs pressure and strain

The variation of the refractive index of liquid with pressure to 14 kbar has been determined by an optical interferometric method. The liquids studied are carbon tetrachloride, n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane, benzene, chlorobenzene, methyl alcohol, and water at room temperature. Since most of these liquids freeze at room temperature even before 14 kbar is reached, the measurements were carried out up to the freezing point or 14 kbar, whichever pressure is lower. In every case the refractive index increases with pressure with pronounced nonlinearity, particularly at high pressure. This nonlinearity is reduced considerably when the same data on Δn are considered as a function of the volume strain indicating that the nonlinear piezo-optic behavior of liquids is just a manifestation of nonlinear P–V relationship. Further, it is found that the slight nonlinearity noticed in the Δn−ΔV/Vo relationship could be still further reduced when the variation in refractive index is treated as functions of the Lagrangian and Eulerian strains. In particular, the Eulerian strain ε is found to yield a much larger range of strain over which a simple linear relationship between Δn and ε is obtained irrespective of the nature of the liquid or the equation of state used to compute the strain.

The effects of cross-section deformations on the displacements of a multiple-shell roof composed of π-shaped elements

The subject of this paper is the analysis, by means of an optical-interferometric method, of the displacements of a multiple-shell roof, composed of π-shaped elements, mutually connected by linear hinges. The first part deals with both the warping of the section (due to combined bending and torsion) and plane cross-section deformations: two different theoretical approaches (‘rigid section’ and ‘deformable section’) are considered, so that experimental and theoretical results can be compared; a linear load is applied to each hinge in turn, In the second part, the effects of diaphragm spacing on the section distortion are analysed in the case of a single prismatic element.

Optical Image Subtraction

There are several methods for optically subtracting one image from another in order to detect differences between scenes or between photographs of scenes. There are many applications for such a technology, including earth resource studies, meteorology, automatic surveillance and/or inspection, pattern recognition, urban growth studies, and bandwidth compression. This paper presents an overview of several techniques for obtaining optical image subtraction, including holographic, interferometric, coding, and positive-negative superposition methods. As part of this review, a table is presented summa-rizing and comparing the characteristics of more than twenty-five approaches. An extensive bibliography is also given.

Polarisationseffekte in der Hyperfeinstruktur von65Cu I, 3d 94s 2 m 2 D

The hyperfinestructure of the transition65CuI, 3d 104p 2 P 3/2—3d 94s 2 m 2 D 5/2 was investigated by optical interferometric methods. For the hfs-factors the following values were found:A(65Cu,m 2 D 5/2)=26,79(3) mK andB(65Cu,m 2 D 5/2)=5,81(10) mK. The core polarization of them 2 D-terms and the Sternheimer corrections in the calculation of the quadrupolmoment of copper 65 from theB-factors of the terms 3d 9 4s2 m 2 D and 3d 10 4p 2 P 3/2. were discussed.

Interferometric measurement of electron density in a high-current discharge

An optical interferometric method has been used to measure the electron density in Sceptre IV for various discharge conditions. The interferometer, which was of the common-path type, was used in conjunction with a rotating mirror camera to find the variations of electron density, integrated across the discharge tube, with respect to space and time. Mean densities of the order of 1014 cm-3 have been measured. Large-scale losses and injection of particles were observed for all discharges, but otherwise the discharge behaviour was very non-reproducible. Low electron densities during the discharge are associated with the mechanism producing the `bars' observed in `streak' photographs taken simultaneously with the interferograms.

The Determination of Residual Stresses in Hardened, Ground Steel

Abstract The residual surface stresses induced by grinding a hardened SAE 4340 steel have been investigated by means of x-ray diffraction and by optical interferometric methods. The depth of penetration of the residual stresses increases as the severity of grinding is increased. The higher the hardness level of the steel, the greater is the absolute value of the residual stress. The magnitude of the residual stresses varies from 100,000 psi in tension to 135,000 psi in compression depending on the hardness level of the steel and the severity of grinding. Light grinding produces residual compressive stresses while heavy grinding produces tensile stresses.