Fringe Separation Research Articles

Shear wave interferometry, an application of sonoelastography

Sonoelastography is an ultrasound imaging technique where low-amplitude, low-frequency (LF) vibration is detected and displayed via real-time Doppler techniques. When multiple coherent shear wave sources exist, shear wave interference patterns appear. Two shear wave sources at the same frequency create hyperbolic shaped interference patterns in homogeneous, isotropic elastic media. Shear wave speed can be estimated from the fringe separation and the source frequency. If the two sources are driven at slightly different sinusoidal frequencies, the interference patterns no longer remain stationary. It is proven that the apparent velocity of the fringes is approximately proportional to the local shear wave velocity. With this approach, local shear wave speed in elastic media can be estimated. In addition, with a single shear wave source at frequency f and the ultrasound probe externally vibrated at frequency f−Δf, a novel type of moving interference between the shear waves and the frame of reference motion is created. The moving interference fringes represent the shape of shear wave wavefronts while traveling at a much slower speed. This approach provides a real-time visualization of shear wave propagation and local wave speed estimation from which local stiffness is inferred. [Work supported by NIH.]

Analysis of HRTEM images for carbon nanostructure quantification

Image processing algorithms have been developed to extract fringe length, tortuosity and separation from high resolution transmission electron microscopy images. To validate the separation algorithm, a comparison is made between the image-based fringe separation and that obtained by analysis of X-ray diffraction data for a progressively heat-treated carbon black. Agreement is favorable. To illustrate the utility of the analysis parameters for a range of carbon nanostructures, analysis is applied to a series of pyrolytically prepared carbon soots – qualitatively described as containing amorphous, graphitic or fullerenic nanostructure. For all processing, the intermediate image, in the form of a skeletonized binary image of the original high resolution transmission electron micrograph, is shown and found to accurately reflect the nanostructural organization within the carbon as visually observed. Statistical results for each analysis parameter, extracted from the binary images, are presented in the form of histograms and quantitatively distinguish the different carbon nanostructures.

Laser-Scattering-Based Method for Investigation of Ultra-Low-Loss Arc Fusion-Spliced Single-Mode Optical Fibers

Standard arc fusion splicing of optical fibers does not include buckling, angular, or lateral offsets. With fusion splicing, a tiny core axial offset exists. It originates from an index modification in the core region due to the heat treatments accompaniment to the splice process. Such axial offset practically contributes to causing the major power loss. In this paper, a new method based on the forward-scattering technique is described to examine standard exactitude ultra-low-loss fusion splicing of single-mode fibers. The method provides the ability to estimate the splice loss. For the first time, a modified scattering pattern is recorded for the spliced intermediate junction of arc fusion-spliced fibers. The deformed scattering pattern takes a diffractionlike shape pattern. The fringe separation between the most two outer solid fringes showed a direct proportionality to the power loss due to splicing. The method could be used to suppress such inescapable axial offset significantly, even in fibers with a large core eccentricity. An ultra-low-loss splicing without conventional power monitoring could be achieved.

First Observations with a Co-phased Six-Station Optical Long-Baseline Array: Application to the Triple Star Virginis

We report on the first successful simultaneous combination of six independent optical telescopes in an interferometric array. This is double the number of independent telescopes, and 5 times the number of independent baselines, heretofore combined simultaneously. This was accomplished with the Navy Prototype Optical Interferometer at Lowell Observatory, near Flagstaff, Arizona. We describe the main technologies demonstrated, including hybrid six-way beam combination, nonredundant multiple optical path modulation for fringe separation, and the fringe detection electronics. To test the array’s suitability for high

Light Figures and Group-to-Phase Velocity Ratio in Anisotropic Media

It is shown that light figures can be employed for determination of the group-to-phase velocity ratio without measurements of the absolute value of refractive index. It is applicable to uniaxial media and, after generalization, to biaxial media. In some cases the sample thickness is not required. The method was applied to weakly biaxial TlInS2 semiconductor-ferroelectric with well-defined light figure patterns at room temperature. It is shown that the obtained results are consistent with the available data on optical transitions near the band gap of this material. In combination with measurements of interference fringe separation in polarized transmission intensity (PTI) spectra the proposed method is supposed to allow for the determination of the absolute values of refractive indices.

Transmission Electron Microscopy and Photoluminescence Characterization of InAs Quantum Wires on Vicinal GaAs(110) Substrates by Molecular Beam Epitaxy

InAs quantum wires have been naturally formed on vicinal GaAs(110) surfaces with giant steps by molecular beam epitaxy. Transmission electron microscope observations reveal the high density of stacking faults and the moire fringe for thick wires (>4 ML) due to the large InAs–GaAs lattice mismatch. From the moire fringe separation, thick InAs wires are found to be completely relaxed. No defect is observed for thin wires (<4 ML). Strongly polarized photoluminescence (PL) observed for InAs wires confirms the carrier confinement to the quantum wire structures and the strain effect induced by the large lattice mismatch. A considerable energy shift is observed in the excitation intensity dependence of PL, indicating large nonuniformity.

Analysis of coseismic surface displacement gradients using radar interferometry&amp;colon; New insights into the Landers earthquake

The map of the coseismic displacement field generated by interferometric processing of synthetic aperture radar &amp;lpar;SAR&amp;rpar; images taken before and after the June 28, 1992, Landers earthquake sequence brings new insights into the nature of deformation caused by these earthquakes. We use the interferometric map generated by Massonnet et al. &amp;lpar;1993&amp;rpar; to analyze the surface displacement field in the vicinity of the fault trace. Complexities in the fringe pattern near the fault reflect short&amp;hyphen;wavelength variations of the surface rupture and slip distribution, and attest to large displacement gradients. Along two sections of the fault, characteristic fringe patterns can be recognized, contrasting in density and direction with patterns observed away from the rupture. In order to understand the observed fringe patterns, we compute synthetic interferograms in three simple cases: &amp;lpar;1&amp;rpar; rigid&amp;hyphen;body rotations about a vertical axis, &amp;lpar;2&amp;rpar; about a horizontal axis &amp;lpar;tilt&amp;rpar;, and &amp;lpar;3&amp;rpar; distributed, simple shear. The orientation and spatial separation of interferometric fringes predicted by these models help constrain near&amp;hyphen;field deformation and rupture parameters. Where the Kickapoo fault connects with the Homestead Valley fault, the interferogram shows a clear pattern of parallel N20&amp;deg;W fringes separated by about 160 m. This pattern and vertical offsets measured along the Kickapoo fault suggest that the block between this fault and the Johnson Valley fault may have been tilted, down to the west. A 5&amp;hyphen;km block lifted by l m on one side would be tilted by an angle of 0.01&amp;deg; &amp;lpar;190 &amp;mu;rad&amp;rpar;, producing fringes separated by about 160 m, parallel to the tilt axis. Such a tilt, parallel to a N20&amp;deg;W direction, would account for the gradual, northward increase of the vertical slip component observed along the Kickapoo fault. This tilt may also explain the 1 m of reverse slip observed along the &amp;ldquo;slip gap&amp;rdquo; section of the Homestead Valley break. Between the southern end of the Johnson Valley fault and the Eureka Peak fault, where no surface rupture has been mapped, the dense pattern of fringes implies distributed shear, probably resulting from fault slip at depth. The density and direction of the fringes in the gap are consistent with a right&amp;hyphen;lateral slip of 1.2&amp;ndash;3.8 m on a blind fault locked above the depth of 1.5&amp;ndash;2 km. Such observations of small wavelength features in the SAR interferogram bring new insights into the near&amp;hyphen;field displacement gradient and thus on response of the uppermost crust to seismic rupture.

Structural characterization of carbon nanotubes and nanoparticles by high-resolution electron microscopy

The fringe separation in high-resolution electron microscopy images of carbon nanotubes changes from equally spaced on both sides of the tube hollow to unequally spaced and expanded on one side when tilted about the tube axis. This observation cannot be explained by the previously proposed equally spaced coaxial shell model. An unequally spaced non-coaxial closed shell nested model is proposed. Unlike the equally spaced imperfect shell model, there are no intrinsic defects and thus no dangling bonds associated with the unequally spaced closed perfect shell nested model. The recently reported compressive and intercalation behaviour of carbon nanotubes can be rationalized in terms of the unequal spacing and morphological defects in the nanotube structure.

Black-and-white fringes and the colors of caustics

Fine-scale interference fringes that decorate caustics produced with white light appear black and white with high contrast. This is surprising, as the elementary expectation, supported by theory and computer simulation, is that the fringes should be highly colored. The fringe separation is several arc minutes and therefore close to the resolution limit of the eye. Under magnification (even of a photograph), the colors are revealed. Therefore black-and-white fringes are an illusion, giving a dramatic naked-eye illustration of the fact that the angular resolution of the visual system is better for luminance than for color.

The 6m mm-VLBI telescope at Kagoshima, Japan

VLBI observations of millimeter wavelengths can probe the broad line emission and jet forming regions of quasars, and the scale of an accretion disk around massive black holes in nearby active galaxies, which are self-absorbed at longer wavelengths. Therefore, the extension of the mm-VLBI network is timely and urgent problem. We are now planning to move Nobeyama 6 m mm VLBI telescope to Kagoshima. The telescope will be placed at Kinkohwan park in Kagoshima City in late 1992 and will be operated in 1993. The frequencies for VLBI observations will range from 22 GHz to 100 GHz.To date, there are two mm-VLBI facilities in Japan: Nobeyama 45 m and Kashima 34 m, However, the longest baseline is only about 200km EW which provides a fringe separation of 17 mas. This is not sufficient for high resolution mapping. A 10 m telescope which is under construction at Mizusawa, 400 km north from Kashima which will be usable up to 43 GHz and will add a north-south baseline, which is very important for astrometrie measurement.

Comparative Holographic Moire Interferometry: Separation Of Moire Fringes From The Carrier Interference Pattern

Comparative holographic moire interferometry (CHMI) permits defect detection by comparison of the mechanical responses of two macroscopically identical specimens at equal loading. In the present work a technique of moire fringe separation is suggested that is amenable to automatic readout. Two approaches are proposed and experimentally verified: phase shifting of the carrier interference pattern and auxiliary carrier fringe generation with subse-quent optical filtering. The phase shifting method is applicable to an additive moire scheme with two reference beams. Auxiliary carrier fringe generation can be used in both additive and multiplicative CHMI. The frequency constraints of the latter method due to the optical recording arrangement and mechanical responses of the tested specimen are analyzed.

Whole-area photoelastic analysis by image processing on the principal-stress direction and separation of isochromatics from isoclinics.

In order to perform an accurate stress analysis in the framework of photoelasticity with computer-aided image processing, it is desireble to obtain the difference of the principal stresses and their directions over the whole area of the model, comparing the calculated result with the experimental data visually in each step of processing. The authors, in this paper, would like to focus on the classical photoelastic method with a plane polariscope. The subjects discussed are as follows : 1) to devise an explicit description of an equation for the direction angle of the principal stresses, analyzing the structural equation of the intensity of light in a plane polariscope, 2) to establish an algorithm for the calculation of the principal-stress direction over the whole area of the model, 3) to verify the effectiveness of the algorithm through various applications with experimantal data, 4) to present a method for more accurate and reliable separation of isochromatic fringes from isoclinic fringes, and, finally, 5) to propose a new method for computer-aided photoelastic analysis which can utilize a limited number of isoclinic patterns.

Observation of two-zone Ramsey fringes using laser Stark spectroscopy of a molecular beam.

Well-resolved Ramsey fringes have been demonstrated using laser Stark spectroscopy of ${\mathrm{CH}}_{3}$F in a molecular beam with two interaction regions. Fringe separations as low as 155 kHz were obtained. The interaction regions were produced by masks containing slits placed in the Gaussian-profile beam of a cw ${\mathrm{CO}}_{2}$ laser. Population inversion resulting from a frequency sweep associated with the curvature of the slit-diffracted wave fronts has limited the observations at high laser-power values. An imaging system has been shown to eliminate this effect. Experiments with three and five laser-molecular beam crossings were also conducted to demonstrate the feasibility of using multiple interaction regions as a tool for high-resolution spectroscopy. The results have been modeled using the optical Bloch equation for a two-level system. Good agreement with the experiment has been obtained.

Tidal mixing in the channel isles region derived from the results of remote sensing and measurements at sea

Satellite images and measurements at sea have identified a pattern of tidal fringes S.W. of Jersey. From the fringe separation it is possible to estimate the residual currents in the region. From the dissipation time scale of the fringes it is possible to derive a value for the non-dimensional coefficient of tidal mixing.

Fatigue crack growth measurement in a CSM composite using compliance and Moiré techniques

In the present work fatigue crack growth tests under constant load conditions were carried out on centre-notched biaxial specimens in order to measure the effects of load biaxiality in air and also in a dilute acidic environment. Initially a compliance calibration technique was used to determine the effective crack length so as to overcome difficulties connected with visual measurement and to present the fatigue results on a fracture mechanics basis when using conventional stress intensity factors. However, the compliance method becomes unreliable when the biaxiality factor is large or the crack length small, so the Moiré fringe technique was used to provide a method independent of biaxiality and probably of the usual environmental effects. Measurement of the fringe separation allowed the crack length to be determined, while dislocations in the fringe pattern showed the crack opening mode. The merits of the two techniques were compared and assessed using the Paris law relationship, based on conventional fracture mechanics.

Wave-front curvature in a Fizeau wavemeter

The effect of imperfect collimation on the fringe separation of a Fizeau wavemeter is calculated. It is shown that illumination in a plane normal to the wedge face and parallel to the wedge axis enables the detector array to be positioned such that the wavelength error caused by spherical wave-front curvature introduced by the beam expander becomes insignificant to 1 part in 10(8), and no dispersion correction for the wedge plate is required. It is also shown that a sealed air wedge is capable of a wavelength precision approaching 1 part in 10(8).

Anomalous wave interference at Z 3-exciton resonance of CuCl

The transmission and the reflection spectra of a thin CuCl single crystal of 0.15μ thickness have been measured in the Z 3-exciton resonance region at 1.6K by using a weak dye-laser light as a light source. Well resolved interference fringes have been obtained over the exciton resonance. In the higher energy region than the longitudinal exciton's energy, the separation of adjacent fringes cannot be explained by interference of the lower branch polariton waves (LBP) or the upper branch polariton waves (UBP). These structures have been explained by the mutual interference effect between the UBP and LBP waves, anomalous waves. This has been confirmed by the measurements of two-photon absorption due to the excitonic molecule via respective polariton states.

Metre Wavelength Solar Radio Bursts with Periodic Modulation

Observations of solar radio bursts in the frequency range 125-150 MHz are described. It is found that their properties are consistent with those observed for similar bursts in the 30-55 MHz range, except that all, rather than just a small proportion, showed periodic intensity maxima or fringes in the frequency-time plane. Fringe separation ?f was found to change with frequency between 30 and 150 MHz according to ?f 8 f 1.48, a result inconsistent with Faraday rotation as the cause of the fringes.

Application of faraday's effect in static and dynamic holographic photoelasticity

The basic principle of applying Faraday's effect to achieve the separation of fringes in static and dynamic holographic photoelasticity, and a study and application of Faraday's light rotator are described in this paper. It is proposed that Faraday's light rotator be used for automating photoelastic instrumentation for measuring isoclinics and the decimal orders of isochromatic fringes.

Folded-wave interferometer for laser-matter interaction studies

A folded-wave interferometer that allows for independent adjustment of the background fringe separation of two output interferograms is described. This white-light wide-angle instrument, based on the Michelson interferometer, has a large field of view limited only by the imaging optics.