Fringe Spacing Research Articles

An adaptive singular value decomposition (SVD) algorithm for analysis of wavelength modulation spectra

Optical interference fringes due to unwanted etalons are often the limiting uncertainty in diode laser spectroscopic trace gas measurements. Temporal variations in the fringe spacings, phases, and amplitudes introduce systematic baseline changes that limit useful signal averaging times to ∼1000 s, and constrain minimum detectable absorbances to between one and three orders of magnitude worse than the fundamental limiting noise sources (shot noise and/or detector thermal noise). We describe an adaptive numerical filtering method based on singular value decomposition (SVD) that shows, for the system studied, a fivefold reduction in baseline drift due to unwanted etalons over a one-week-measurement period. The adaptive algorithm is fast (<1 ms per computation), robust, and uses linear methods. It is computationally equivalent to principal component analysis (PCA). The test system was acetylene detected using a near-infrared telecommunications laser operating at 6541.96 cm-1. The gas detection limit was 20 ppb (1σ) over the one-week measurement.

Fringe spacing and phase of interfering matter waves

We experimentally investigate the outcoupling of atoms from Bose-Einstein condensates using two radio-frequency (rf) fields in the presence of gravity. We show that the fringe separation in the resulting interference pattern derives entirely from the energy difference between the two rf fields and not the gravitational potential difference between the two resonances. We subsequently demonstrate how the phase and polarization of the rf radiation directly control the phase of the matter wave interference and provide a semiclassical interpretation of the results.

Turbo machine tip clearance and vibration measurements using a fibre optic laser Doppler position sensor

This paper presents a novel fibre optic laser Doppler position sensor for single blade tip clearance and vibration measurements at turbo machines, which offers high temporal resolution and high position resolution simultaneously. The sensor principle is based on the generation of a measurement volume consisting of two superposed fan-like interference fringe systems with contrary fringe spacing gradients using wavelength division multiplexing. A flexible and robust measurement system with an all-passive fibre coupled measurement head has been realized employing diffractive and refractive optics. Measurements of tip clearance and rotor vibrations at a transonic centrifugal compressor performed during operation at up to 50 000 rpm (833 Hz) corresponding to 21.7 kHz blade frequency and 586 m s−1 blade tip velocity are presented. The results are in excellent agreement with those of capacitive probes. The mean uncertainty of the position measurement was around 20 µm and, thus, considerably better than for conventional tip clearance probes. Consequently, this sensor is capable of fulfilling the requirements for future active clearance control systems and has great potential for in situ and online tip clearance and vibration measurements at metallic and non-metallic turbine blades with high precision.

Triple-biprism electron interferometry

Triple-biprism electron interferometry has been developed to flexibly control all interference parameters, i.e., interference region (size and shape), fringe spacing, and fringe angle. Each filament electrode of the upper and middle electron biprisms is installed in the individual image planes of the objective and first magnifying lenses, respectively. One more filament electrode of the lower biprism is set between the crossover plane and image plane behind the second magnifying lens. The azimuth angle between the upper and middle filaments is set at 90°, and lower filament is set at about 45° for both of the above filaments. Among many possible optical setups, we chose the setup with the easiest and most flexible control of all the interference parameters through theoretical investigation and experimental confirmation. The interferometer was constructed in a 1×106V field emission electron microscope, and the overall performance was demonstrated and investigated experimentally.

Formalism for testing theories of gravity using lensing by compact objects. III. Braneworld gravity

Braneworld gravity is a model that endows physical space with an extra dimension. In the type II Randall-Sundrum braneworld gravity model, the extra dimension modifies the spacetime geometry around black holes, and changes predictions for the formation and survival of primordial black holes. We develop a comprehensive analytical formalism for far-field black hole lensing in this model, using invariant quantities to compute all geometric optics lensing observables. We then make the first analysis of wave optics in braneworld lensing, working in the semi-classical limit. We show that wave optics offers the only realistic way to observe braneworld effects in black hole lensing. We point out that if primordial braneworld black holes exist, have mass M, and contribute a fraction f of the dark matter, then roughly 3e5 x f (M/1e-18 Msun)^(-1) of them lie within our Solar System. These objects, which we call "attolenses," would produce interference fringes in the energy spectra of gamma-ray bursts at energies ~100 (M/1e-18 Msun)^(-1) MeV (which will soon be accessible with the GLAST satellite). Primordial braneworld black holes spread throughout the universe could produce similar interference effects; the probability for "attolensing" may be non-negligible. If interference fringes were observed, the fringe spacing would yield a simple upper limit on M. Detection of a primordial black hole with M <~ 1e-19 Msun would challenge general relativity and favor the braneworld model. Further work on lensing tests of braneworld gravity must proceed into the physical optics regime, which awaits a description of the full spacetime geometry around braneworld black holes.

Optical phase-conjugation studies in Acid blue 9 dye-doped gelatin film using low-power He–Ne laser

We report on the observation of optical phase-conjugation (OPC) in Acid blue 9 dye-doped gelatin film using a low-power continuous-wave (He–Ne, 633 nm, 35 mW) laser by the degenerate four-wave mixing (DFWM) method. The intensity of the phase-conjugate signal was measured as a function of time of exposure. The phase-conjugate signal contributions from induced transmission and reflection gratings were measured. The fringe spacing (Λ) of the transmission and reflection gratings formed in the Acid blue 9 dye film were calculated as 5.12 and 0.32 µm respectively.

Determination of Thermal Diffusivities, Thermal Conductivities, and Sound Speeds of Room-Temperature Ionic Liquids by the Transient Grating Technique

We report measurements of thermal diffusivity of several room-temperature ionic liquids (RTILs) using the transient grating method. Measurements are carried out using ionic liquids with small concentrations of an inert dye that is excited by the 532 nm output of a Nd:YAG laser in a grating with a fringe spacings of (92 and 104) μm. The experiments give thermal diffusivities from which thermal conductivities can be determined, sound speeds, and acoustic damping parameters for seven ionic liquids. In this study, we have used combinations of the cation 1-butyl-3-methylimidazolium ([BMIm]+) with the anions tetrafluoroborate ([BF4]-), hexafluorophosphate ([PF6]-), and bis(trifluoromethylsulfonyl)imide ([Tf2N]-) and combinations of the anion [Tf2N]- with the cations 1-ethyl-3-methylimidazolium ([EMIm]+), 1-pentyl-3-methylimidazolium ([PMIm]+), 1-hexyl-3-methylimidazolium ([HMIm]+), and 1-octyl-3-methylimidazolium ([OMIm]+) to determine the effect of anion and cation on the thermophysical properties of the RTILs...

X-ray phase contrast imaging at MAMI

Experiments have been performed to explore the potential of the low emittance 855MeV electron beam of the Mainz Microtron MAMI for imaging with coherent X-rays. Transition radiation from a micro-focused electron beam traversing a foil stack served as X-ray source with good transverse coherence. Refraction contrast radiographs of low absorbing materials, in particular polymer strings with diameters between 30 and 450μm, were taken with a polychromatic transition radiation X-ray source with a spectral distribution in the energy range between 8 and about 40keV. The electron beam spot size had standard deviation σh = (8.6±0.1)μm in the horizontal and σv = (7.5±0.1)μm in the vertical direction. X-ray films were used as detectors. The source-to-detector distance amounted to 11.4m. The objects were placed in a distance of up to 6m from the X-ray film. Holograms of strings were taken with a beam spot size σv = (0.50±0.05)μm in vertical direction, and a monochromatic X-ray beam of 6keV energy. A good longitudinal coherence has been obtained by the (111) reflection of a flat silicon single crystal in Bragg geometry. It has been demonstrated that a direct exposure CCD chip with a pixel size of 13×13μm^2 provides a highly efficient on-line detector. Contrast images can easily be generated with a complete elimination of all parasitic background. The on-line capability allows a minimization of the beam spot size by observing the smallest visible interference fringe spacings or the number of visible fringes. It has been demonstrated that X-ray films are also very useful detectors. The main advantage in comparison with the direct exposure CCD chip is the resolution. For the Structurix D3 (Agfa) X-ray film the standard deviation of the resolution was measured to be σf = (1.2±0.4)μm, which is about a factor of 6 better than for the direct exposure CCD chip. With the small effective X-ray spot size in vertical direction of σv = (1.2±0.3)μm and a geometrical magnification of up to 7.4 high-quality holograms of tiny transparent strings were taken in which the holographic information is contained in up to 18 interference fringes.

Measurements of velocity–acceleration statistics in turbulent boundary layers

An advanced laser Doppler velocimetry system is developed to acquire measurements of fluctuating velocity–acceleration statistics in turbulent boundary layers. These correlations are enabled by customized burst signal processing that estimates both the Doppler frequency and the rate-of-change of Doppler frequency, which are related to the particle velocity and acceleration by the interference fringe spacing. The measurements give important insight into the near-wall turbulence structure since the statistical correlations of interest, u i a j ¯ appear directly in the Reynolds stress transport equations as a sum of the velocity–pressure gradient correlation, - 1 ρ u i ∂ p ∂ x j + u j ∂ p ∂ x i ¯ , the dissipation rate, 2 ν ∂ u i ∂ x k ∂ u j ∂ x k ¯ , and the viscous diffusion, ν ∇ 2 u i u j ¯ . The immediate power of such measurements is that combinations of terms in the Reynolds stress transport equation may be characterized by a single statistical measurement at one location in the flow—no gradients need be computed. In the present paper, data are presented for a constant-pressure 2D turbulent boundary layer at Re θ = 6800. Near-wall results for the dominant term in the velocity–acceleration tensor, the streamwise correlation ua x ¯ , compare favorably with DNS for the same quantity at Re θ = 1410 and Re τ = 640; furthermore, the quantity exhibits no Reynolds number effects within experimental uncertainties. The balance of the velocity–acceleration equation in the streamwise direction is presented, giving the first measurements for the profile of the velocity–pressure gradient correlation with this technique. This study exhibits the potential of the technique to be applied to more complex flows, particularly those 3D separating flows in which the motions contributing to the velocity–acceleration correlations become dominant.

Synthesis and Characterization of Mo‐Oxide Nanoribbons

Mixed valence Mo‐oxide nanoribbons have been synthesized using MoO3 as precursor and hexadecylamine (HDA) as surfactant under hydrothermal condition at 180°C for 1 to 10 d. The morphology of the product is found to depend strongly on the duration of hydrothermal treatment, temperature and HDA/Mo ratio. The powder diffraction patterns of pre‐and post‐hydrothermally treated materials exhibit the highly intense and sharp reflections at low scattering angles that are typical for layered structures. The IR spectrum of Mo‐HDA composite is quite similar to hydrothermal treated samples except shifting of few bands to higher energy side. The weight change in TG‐DTA curves indicates the presence of HDA as intercalates. The SEM images of samples reveal the layered and flat nanoribbons formation. Dimensions of these flat nanoribbons found from SEM images are about 160 nm in thickness, 430–620 nm in width and several micrometers in length. The high resolution TEM images of Mo‐oxide nanoribbons corroborate the XRD results and the fringe spacing paralleling to the nanolayers is estimated to be 3.52 nm, which is close to the (001) lattice spacing of lamellar Mo‐oxide nanoribbons.

Reconstruction technique for off-axis electron holography using coarse fringes

A reconstruction technique for off-axis electron holography not requiring Fourier transformation is presented. Background intensity and amplitude modulation recorded in a hologram are normalized using an envelope function, and a cosine-function image corresponding to interference fringes is retrieved from the hologram. A reconstructed phase image is then calculated from the retrieved cosine image. After phase unwrapping, the phases due to carrier frequency and Fresnel diffraction from the biprism are removed using a reference hologram, and the corrected phase image is obtained. One advantage of this method is that the spatial resolution does not rely on the interference fringe spacing. Another advantage is that the phase image has no artifacts due to windowing of the sideband, which occurs in the usual Fourier-transformation method. Details of the calculation process and demonstrations of the method using a latex sphere particle and self-assembled Co nanoparticles are described.

Array Formation in Evanescent Waves

A chessboard pattern: Polystyrene particles form arrays at the silica–water interface, trapped in the evanescent field of two counterpropagating laser beams (see figure; particle size: 460 nm). In the horizontal direction, the periodicity of the array is twice the spacing of the interference fringes of the laser beam. In the vertical direction, the periodicity depends on the particle diameter and the ionic strength, which affects the repulsive potential between the charged latices.

Topographical Mapping of Surface and Interface Profiles by Using Acoustic Interferometry

The model is presented to explain formation of interference fringes appearing in acoustic images obtained by the acoustic microscopy. In the model, the residual vibration in the vibrator is overlapped by the vibration due to the ultrasonic wave reflected from the surface of the solid. The model was confirmed by the periodical change in the output of the vibrator with the water path. Then acoustic images of an inclined glass plate were observed to examine the influence of the inclination angle, the focal position and the wave frequency on the fringe spacing. A height difference corresponding to the fringe spacing was about a half wavelength of the ultrasonic wave in water. The interference fringes were also observed with a specimen with a deep notch under bending test and showed a good agreement with moire fringes. The presented model suggests that the interference fringes are also formed corresponding to profiles of a reverse surface and a boundary between dissimilar substances. This was confirmed by acoustic images of copper plates with a tapered edge and a shallow groove on the reverse surface, and also those of a copper plate with a dint on the reverse surface, covered by tin alloy solder.

Synthesis, Structure, and Electrochemical Properties of Li4Ti5O12

ABSTRACTLithium titanium oxide (Li4Ti5O12) spinels are promising negative electrode materials for application in energy technology. In this work, we have synthesized Li4Ti5O12 and investigated its structure, electronic properties, and electrochemical features using several analytical spectroscopy and microscopy techniques. The equally spaced lattice fringes obtained using by the high-resolution transmission electron microscopy (HRTEM) along with electron diffraction reveal that the grown Li4Ti5O12 is well crystallized in the spinel structure without any indication of crystallographic defects such as dislocations or misfits. The electronic structure determination using high-resolution X-ray photoelectron spectroscopy (XPS) coupled with compositional studies using energy dispersive X-ray spectrometry (EDS) indicate excellent chemical quality of the Li4Ti5O12. Under the optimal synthetic condition, the sample delivers a discharge capacity of 161 mAh/g at C/12. The good cyclability of Li4Ti5O12 is attributed to the small expansion (δV≈1%) of the elementary unit-cell.

Aspects regarding measurement of thickness of intergranular glassy films

Materials such as Si(3)N(4), SiC and SrTiO(3) can have grain boundaries characterized by the presence of a thin intergranular amorphous film of nearly constant thickness, in some cases (e.g. Si(3)N(4)) almost independent of the orientation of the bounding grains, but dependent on the composition of the ceramic. Microscopy techniques such as high-resolution lattice fringe imaging, Fresnel fringe imaging and diffuse dark field imaging have been applied to the study of intergranular glassy films. The theme of the current investigation is the use of Fresnel fringes and Fourier filtering for the measurement of the thickness of intergranular glassy films. Fresnel fringes hidden in high-resolution micrographs can be used to objectively demarcate the glass-crystal interface and to measure the thickness of intergranular glassy films. Image line profiles obtained from Fourier filtering the high-resolution micrographs can yield better estimates of the thickness. Using image simulation, various kinds of deviation from an ideal square-well potential profile and their effects on the Fresnel image contrast are considered. A method is also put forth to objectively retrieve Fresnel fringe spacing data by Fourier filtering Fresnel contrast images. Difficulties arising from the use of the standard Fresnel fringe extrapolation technique are outlined and an alternative method for the measurement of the thickness of intergranular glassy films, based on zero-defocus (in-focus) Fresnel contrast images is suggested. The experimental work is from two ceramic systems: Lu-Mg-doped Si(3)N(4) and SrTiO(3) (stoichiometric and nonstoichiometric). Further, a comparison is made between the standard high-resolution lattice fringe technique, the standard Fresnel fringe extrapolation technique and the methods of analyses introduced in the current work, to illustrate their utility and merits. Taking experimental difficulties into account, this work is intended to be a practical tool kit for the study of intergranular glassy films.

104 低コヒーレンス干渉を利用した断面内速度場計測(2)(OS1-1 光工学による流体計測法の応用と新展開,OS1 光工学による流体計測法の応用と新展開,オーガナイズドセッション)

An imaging interferometer with low-numerical-aperture objectives and a CCD camera is proposed and studied for application to a particle image velocimetry (PIV) system. Sectional images are obtained based on the optical coherence tomography with the lateral resolution about 40μm. The motion of tracer particles within a coherence gate are detected from difference images between video frames and vector maps are obtained by using auto-correlation PIV. Two types of particle image acquisition conditions are found according to the fringe spacing, which affects the detected motion of tracer particles.

Realization of POLICRYPS Gratings: Optical and Electro-Optical Properties

ABSTRACT In this paper we report a detailed characterization of a new structure (POLICRYPS) in which liquid crystal films are completely separated by polymer slices. This structure behaves as a Bragg diffraction grating and exhibits efficiencies that can become as high as 96–98%. The temperature dependence of the diffraction efficiency can be explained in terms of a Kogelnik-like model. A numerical simulation has been implemented which makes use only of real values of physical quantities and accounts for the experimental results with good accuracy. An applied electric field is able to switch off the grating, with a characteristic switching time which is lower than 1 ms. Threshold values of the field vary in the range 3–5 V/μm for gratings with a 1.39 µm fringe spacing.

Fringe projection profilometry with nonparallel illumination: a least-squares approach

Under a nonparallel illumination condition, fringe patterns projected on an object have unequal fringe spacing that would introduce a nonlinear carrier phase component. This Letter describes a nonlinear carrier removal technique based on a least-squares approach. In contrast with conventional methods, the proposed algorithm would not magnify phase measurement uncertainty, nor does it require direct estimation of system geometrical parameters. The theoretical expression of the carrier phase function on the reference is derived and expanded in a power series. The unknown coefficients in the series are determined by a least-squares method. By subtracting the calculated carrier phase function from the unwrapped phase map, the phase distribution of the object profile is obtained.

아날로그 신호처리를 이용한 백색광 간섭 피크의 검출

A signal processing method for white light interferometry (WLI), which performs a series of analog signal processing steps to locate the central interference fringe position at high speed: is developed and applied to a WLI temperature sensor system. We found that the new method has random walk of with good linearity. However, the temperature change in the path-matching interferometer results in drift of the measured sensor output. The temperature dependence of drift in the WLI temperature sensor system, was calculated to be . It is also found that the relationship between the peak spacing in the interferogram and the spacing measured by the method can be nonlinear when the fringe spacing is comparable to the coherence length of the source.

Structural evolution of turbostratic carbon nitride after being treated with a pulse discharge

Turbostratic carbon nitride was prepared by the pyrolysis of melamine and then treated with a pulse discharge for different times. It is found that after this high-temperature short-time treatment, the structures of the products have changed while the high nitrogen content has been effectively maintained. The obtained product was characterized by X-ray diffraction and infrared spectroscopy. The composition was measured by an element analyzer. An orthorhombic CN x phase has been obtained, identified by transmission electron microscopy coupled with selected area electron diffraction. High-resolution transmission electron microscopy revealed that the product has some nanocrystals having a fringe spacing of approximately 0.32 nm, which embedded in a turbostratic matrix.