Laser Interferometric Technique Research Articles

Interferometric measurement of the physical constants of laser dye solvents

The absolute value of refractive index and its variation with temperature of benzene and chloroform at He-Ne laser wavelength 6328 Å are measured. The measurements are carried out using laser interferometric technique. This technique is based on the shift of interference pattern when rotating the sample in one arm of a newly developed Mach–Zehnder interferometer. The refractive index shows a linear relationship with temperature in the range of interest. The thermal refractive index coefficients of benzene and chloroform are all negative. Applying Maxwell’s theory and Lorentz–Lorenz function, the obtained results are used for calculating the optical permittivity (or dielectric susceptibility) as a function of temperature and many other important related physical constants.

Mach–Zehnder optical system as a sensitive measuring instrument

A laser interferometric measurement technique that uses a Mach-Zehnder interferometer is developed. This technique permits studies of the physical processes that involve a change in the refractive index with temperature to a high degree of accuracy. A theoretical derivation has been formulated to permit computation of the refractive index of transparent materials. The technique is particularly useful in studying slight changes in refractive index of various gases, solutions over a considerable region, and flow patterns in wind tunnels.

Time Dependent Indentation Testing At Non-Ambient Temperatures Utilizing the High Temperature Mechanical Properties Microprobe

AbstractTime dependent indentation data for pure indium from -100 °C to 75 °C is presented. The properties reported include hardness, indentation strain rate, stress exponent and apparent activation energy for creep. These properties were measured using a depth-sensing indentation system capable of performing experiments between -100 °C and 300 °C in ultra-high vacuum. In addition, by employing laser interferometric techniques, this system can obtain displacement data with time constants as low as 50 ns. This allows the investigation of the material response to very fast stress changes over an extremely wide range of strain rates. The adverse and beneficial dynamic effects of step-loading the indenter into the surface of the material will be discussed. Initial results obtained from this type of experiment show that it is possible to obtain energy dissipation or damping information from the material being studied.

Dynamic bore/interaction effects on metal armature performance (railguns)

It is pointed out that metal armatures must be designed to accommodate dynamic bore-armature interaction under electromagnetic loading. High forces must be maintained to ensure low-voltage, nonarcing metal-to-metal contacts. This contact force must be maintained despite relative rail and armature motion. The authors have measured railgun barrel and armature dynamic motion and contact forces, due to electromagnetic loading. They have measured rail motion when subjected to electromagnetic loading, for several different barrel designs using laser interferometric techniques. They have also determined armature contact forces from in situ measurements using load cells. They describe the experiments, and results, and their assessment of the design requirements imposed by these data.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Thickness-direction coefficient of thermal expansion measurement of thin polymer films

A highly sensitive capacitance-change technique, suitable for thin polymer films, has been developed for the measurement of the coefficient of thermal expansion (CTE) in the film-thickness direction. Using this technique, we have determined the thickness-direction CTE of Kapton polyimide to be about 81±4 ppm/°C, averaged over the temperature range 50–150 °C. This polymer was chosen because it is widely used in the electronics industry for the fabrication of flexible printed circuits. Two other techniques, a Fabry–Perot laser interferometric technique, and the more conventional but less sensitive thermomechanical analysis, were also investigated. The thickness-direction CTEs obtained from the three techniques were at least a factor of 2.4 greater than the in-plane CTE of about 34±2 ppm/°C. The in-plane CTE, found here via simple length measurements, was in good agreement with literature values. It is speculated that the CTE anisotropy observed might be due to the in-plane molecular orientation of the polymer chains.

Locally varying particle masses due to a scalar fifth-force field

If a scalar field mediates a fifth force, masses of elementary particles will be affected locally by massive sources, resulting in a change of size of macroscopic objects. The effect is shown to be testable by using an ultra-sensitive laser interferometric technique when it is fully developed for the use in gravity-wave detectors.

Laser interferometric techniques in orthopaedics

(1991). Laser interferometric techniques in orthopaedics. Journal of Medical Engineering & Technology: Vol. 15, No. 6, pp. 209-221.

Direct measurement of the piezoelectric shear coefficient d15 under non-resonant conditions

A new method is developed to measure the piezoelectric shear coefficient d 15 at low frequency (100–400 Hz) using a laser interferometer technique. The d 15 coefficient of PZT-5 was measured by detecting the shear strain excited by an ac electric field under non-resonance conditions. The d 15 coefficient obtained this way is 647 pC N ( ± 16 pC N ) and is in good agreement with the value published in the literature. The d 15 coefficient is also confirmed by measuring the electromechanical coupling coefficient k 15 under the resonance condition (the value is 603 pC N ). The advantage of the new method is that the measurement can be done under non-resonance conditions, the electric field level is precisely known and the non-linearity in d coefficient can be determined down to very low field levels.

Static and dynamic deformations stimulated by ion implantation

The laser interferometric technique has been applied for the investigation of the quasi-static and dynamic components of the elastic deformation of crystalline silicon wafers during implantation of Ar + and He + ions. The absolute values of the integral stress and the amplitude of deformation vibrations are measured as a functions of implanted ions dose, energy and current density and compared with the dose dependencies of the surface acoustic waves (SAW) velocity in the implanted layer. The correlation between integral stress, amplitude of vibrations and SAW velocity variations is shown.

The use of organosilicon polymers in multilayer plasma resist processing

The unique resistance of organosilicon polymers to oxygen plasmas has led to their widespread use in multilayer resist processing. A study of their etching properties shows a correlation between their structure and etching characteristics. Often, these characteristics are obtained by means of laser interferometric techniques. Using a model of this laser signal we have identified various processes which combine to form an oxygen plasma resistant layer atop these organosilicon polymers. In particular, we have discovered that the etching characteristics of these polymers is relatively independent of the specific structure. Rather, the silicon content of these polymers plays the dominant role in providing resistance to these plasmas. For polymers having a high silicon content, the laser signal is regular and sinusoidal; for lower concentrations (<10%), the laser signal shows irregularities which can be explained by means of the model. From an analysis of these laser traces and a comparison to the model, we show that the process of formation of a resistant “oxide” layer is dependent upon the temperature during etching and that other organometallic polymers show a similar behaviour.

Measurement of mean velocities, velocity fluctuations and Reynolds stresses in a turbulent jet with a modified laser interferometric technique

A new optical technique for the measurement of flow velocities with a laser interferometric technique was reported by Menn et al. (1981). Since then the technique has been improved and the authors describe the technique as well as a digital signal processing procedure which has been developed to computer the velocity components from the signal acquired. The method was used to measure velocity fluctuations and Reynolds stresses in an axisymmetric circular air jet. Experimental results are presented and compared with measurements of previous researchers.

Compression and polymorphism of potassium to 400 kbar

Both the compression and polymorphism of K were investigated to about 400 kbar at room temperature in a diamond-anvil pressure cell by optical and X-ray diffraction techniques. The ambient b.c.c.-K(I) is stable to about 120 kbar. The compression data for K(I), fitted to the Birch equation of state, yielded the zero-pressure bulk modulus B 0 = 29.9 ± 0.2 kbar and its first pressure derivative B' 0 = 4.15 ± 0.10. These values agree very well with those of recent data derived from the direct measurement of length changes using piston-displacement (to 20 kbar) and laser interferometer (to 7 kbar) techniques. On the basis of the compression data for K(I) alone, Bridgman's pressure scale may be overestimated by about 10 kbar at 100 kbar and that of Kennedy and LaMori may be underestimated by about 5 kbar at 50 kbar. Two high-pressure polymorphs of K were revealed in the pressure range 100–200 kbar. The b.c.c. → f.c.c. transition in K was observed to occur near 120 kbar, accompanied by a −2.5% discontinuous change in volume. The sample changes gradually from silver to gold in the range 130–150 kbar. The f.c.c.-K.(II) transforms further into an as yet undetermined structure between 170 and 190 kbar. No change in colour was observed in the latter transition. K(III) is stable up to at least about 400 kbar. The equation of state for the f.c.c. phase of K cannot be established. The volume of K was compressed more than 60% in the vicinity of 200 kbar, however.

Instrument for velocity and size measurement of large particles

A new instrument for velocity and size measurement of large particles in two-phase flows was introduced and demonstrated. This instrument which is based on the laser interferometer technique uses two Ronchi gratings. The two separate diffraction modes formed by the gratings interfere with each other and generate the necessary fringe pattern. The instrument can be continuously matched to particles from 100 μm to the centimeter range.

Lithium [Li*(2 2P J)] fine structure transitions and quenching induced by collisions with molecular hydrogen [H2, D2

Dye laser excitation and interferometric fluorescence analysis techniques were used to measure collision induced quenching and fine structure transition rate coefficients in the 7Li*(2 2PJ)+H2,D2 systems at a temperature of 564 K. The quenching and fine structure transition energy transfer processes all occur at ’’gas kinetic’’ rates, but the magnitudes of cross sections for each process are determined by different electronically nonadiabatic interactions at different ranges of internuclear separation. Fine structure transition cross sections are determined by the forms of long range interaction potentials, which are undoubtedly very similar to those of the isoelectronic Li*(2 2PJ)+He system. Quenching cross sections are determined by short-to-intermediate range interaction potentials, some of which may effectively be coupled by fine structure transitions. Simple dynamical models provide limited insight into these rate processes, suggesting that ab initio potential hypersurface calculations plus refined quantal and/or semiclassical dynamical computations using these hypersurfaces are required for proper treatment of the Li*(2 2PJ)+ H2,D2 systems.

Lithium [Li*(2 2P1/2,3/2)] fine structure transitions induced by collisions with noble gas atoms

Dye laser excitation and interferometric fluorescence analysis techniques were used to determine collision induced fine structure transition rate coefficients in the Li*(2 2PJ)+ He, Ne, Ar, Kr, and Xe systems at a temperature of 555.7 K. All the noble gases induce transitions at ’’gas kinetic’’ rates, but differences in the individual magnitudes of the rate coefficients are probably sensitive to the long range portions of the Li*(2 2PJ)–noble gas interaction potentials. There is no appreciable isotope effect for 6Li*/7Li*+He, Ne, Ar systems. Simple models based upon localized transition concepts do not agree adequately with experimental results, suggesting that full dynamical computations using quantal and/or refined semiclassical formalisms are probably required for proper treatment of the Li*(2 2PJ)–noble gas systems and for stringent tests of various choices for the interaction potentials.

Optical interferometric observation of magnetostrictive vibration

A non-contact observation of magnetostrictive vibrational displacements in a rod and a disk of polycrystal nickel is made by means of a laser interferometric technique. It is found this interferometric method is quite reliable. The magnetostrictive vibrational displacements are measured easily with an error less than 10 Å.

A new measuring method of magnetostrictive vibration

A new method for measuring magnetostrictive vibrational displacements has been developed by utilizing a laser interferometric technique with sensitivity enough to detect a vibrational displacement of 10 Å. The most striking merit of this method is that a non-contact and reaction free measuring is essentially permitted. The reliability of this interferometric method is checked by measuring vibrational displacements of a cylindrical nickel rod specimen by means of both the present method and the conventional strain gauge method simultaneously. It is found that the agreement between the two experimental results obtained on the basis of these methods is very good. Therefore, it is concluded that the present interferometric method is quite reliable. The magnitude and the sign of the magnetostrictive vibrational displacements of the cylindrical rod specimens of a single crystal nickel and a polycrystal Ni60-Fe40 alloy are measured by means of the present interferometric method. Satisfactory results are obtained.

Microfabrication and evaluation of diffractive optical filters prepared by reactive sputter etching

Single or linearly superimposed square-wave surface-relief patterns in a transparent plate yield optical transmission characteristics similar to those of interference filters. Reactive sputter etching of fused quartz in CHF3 using Shipley 1350 H photoresist as an etch mask offers a well-controlled method to produce these complex structures. Gratings with periodicities of 1–2 μm and depths of up to 3 μm are fabricated with dimensional tolerances of ±0.02 μm using laser interferometric techniques. Superposition is obtained by successive masking and etching operations. The optical transmission characteristics of these diffractive filters are analyzed and compared with rigorous diffraction theory.

Crack-Tip Damage and Fracture Toughness of Boron/Aluminum Composites

The fracture behavior of center notched unidirectional boron/aluminum composite under tensile loading has been investigated. Load-crack opening displacement (COD) curves were obtained for crack length-to-width ratios varying from 0.05 to 0.5. The COD was measured across the crack surfaces by means of the laser interferometric technique (gage length of 500 μm). As expected, the interferometric displacement gage (IDG) was found to be very sensitive to the appearance of damage at the crack tip, resulting in highly nonlinear load-COD curves. The damage at the crack-tip has been carefully examined by radiographs, SEM, photomicrographs, interfero metric miscroscope and optical interferometry technique. Fracture strength results and experimental load-COD curves were compared with analytical predictions and an excellent agreement has been established. The resistance curve method has also been tried and found to be non- applicable. An understanding of the correlation between the observed failure modes and deformation characteristics has been achieved.

K-Calibration of Unidirectional Metal Matrix Composites

Load-displacement curves were obtained for center notch unidirectional boron/aluminum and borsic/titanium composites. Far field displacements, obtained by means of two standard clip gages, 1 and 0.25 inch long, respectively, were used to establish the variation of global compliance with crack length. The local compliance curve was obtained from the crack opening displacement (COD) measured across the crack surfaces by means of the laser interferometric technique. The Interferometric Displacement Gage (IDG), which is more sensitive to the appearance of damage at the crack tip, yielded nonlinear load displacement curves and seemed to better characterize the fracture behavior of composites. The experimental com pliance curves and the K-calibration results were found to be in good agreement with analytical predictions. The K-calibration curves of the com posites studied were found to be almost equal to that of the isotropic materials; both compliances were predictable by using the isotropic K- calibration.