Interference Fringe Pattern Research Articles

Interferometric measurements of dynamic changes of tear film

Tear film stability plays an important role in the quality of vision. We present an interferometric method for assessing the stability of precorneal tear film in real time. A lateral shearing technique is applied as a noninvasive and sensitive method for investigating tear film stability and the smoothness of the tear film surface by quantitative evaluation of the interference fringe pattern. The evaporation of tears and the appearance of tear film break-up between blinks cause changes in the fringe geometry. For quantitative assessment of the fringe smoothness and consequently of the tear film structure, the fast Fourier transform (FFT) is applied. Four parameters are used to quantitatively estimate dynamic changes in the tear film stability of the cornea 20 s after the eye blink. Examples of examined interferograms recorded in patients with healthy eyes, patients suffering from dry-eye syndrome, and patients wearing contact lenses are given. Significant differences between the stability of the tear film in the healthy eye and that in the dry eye and the eye with a contact lens are observed. The favorable influence of artificial tears applied in patients with dry-eye syndrome or contact lenses is also discussed.

Analyzing interference-fringe patterns by discriminating the features of wavelet maps of symmetric wavelets

This paper shows a connection between the lines of extrema of a three-dimensional wavelet map obtained by means of symmetric wavelets and the position of the fringes of an interference pattern. An algorithm is proposed that makes it possible to discriminate the lines of extrema of interference-fringe patterns

Projection measurement of the maximally entangledN-photon state for a demonstration of theN-photon de Broglie wavelength

We construct a projection measurement process for the maximally entangled N-photon state (the NOON-state) with only linear optical elements and photodetectors. This measurement process will give null result for any N-photon state that is orthogonal to the NOON state. We examine the projection process in more detail for N=4 by applying it to a four-photon state from type-II parametric down-conversion. This demonstrates an orthogonal projection measurement with a null result. This null result corresponds to a dip in a generalized Hong-Ou-Mandel interferometer for four photons. We find that the depth of the dip in this arrangement can be used to distinguish a genuine entangled four-photon state from two separate pairs of photons. We next apply the NOON state projection measurement to a four-photon superposition state from two perpendicularly oriented type-I parametric down-conversion processes. A successful NOON state projection is demonstrated with the appearance of the four-photon de Broglie wavelength in the interference fringe pattern.

Application of an optical interferometer for measuring the surface contour of micro-components

The application of an optical interferometric system using a Mireau objective to measure the surface profile of micro-components is described. The proposed system produces a uniform monochromatic illumination over the test area and introduces an interference fringe pattern localized near the test surface. Both the interference fringes and the 2D image of the test surface can be focused by an infinity microscope system consisting of a Mireau objective and a tube lens. A piezoelectric transducer (PZT) attached to the Mireau objective can move precisely along the optical axis of the objective. This enables the implementation of phase-shifting interferometry without changing the focus of a CCD sensor as the combination of the Mireau objective and the tube lens provides a depth of focus which is deep in comparison to the phase-shifting step. Experimental results from surface profilometry of the protrusion/undercut of a polished fibre within an optical connector and of the curved surface of a micromirror demonstrate that features in the order of nanometres are measurable. Measurements on standard blocks also show that the accuracy of the proposed system is comparable to an existing commercial white-light interferometer and a stylus profilometer.

Digital Recording of Interference Fringe Patterns Reconstructed by Reflection Hologram in the Course of Residual Stresses Determination

Digital Recording of Interference Fringe Patterns Reconstructed by Reflection Hologram in the Course of Residual Stresses Determination

Spectral Domain Optical Coherence Tomography: a Better OCT Imaging Strategy

This paper reviews the current state of research in spectral domain optical coherence tomography (SDOCT). SDOCT is an interferometric technique that provides depth-resolved tissue structure information encoded in the magnitude and delay of the back-scattered light by spectral analysis of the interference fringe pattern. There are two approaches to SDOCT--one that uses a broadband source and a spectrometer to measure the interference pattern as a function of wavelength and the other that utilizes a narrowband tunable laser that is swept linearly in k approximately 1/lambda space during spectral fringe data acquisition. Unlike time domain (TD) OCT, the reference arm is stationary in both SDOCT methods, which allows for ultra high-speed OCT imaging. Owing to its high speed and superior sensitivity, SDOCT has become indispensable in biomedical imaging applications. After a brief introduction and a discussion on sensitivity advantage, methods of implementation of the two SDOCT schemes will be presented. The two peer approaches are compared in speed, scan depth range, complexity, spectral regions of operation, and methods of detection. The review also discusses OCT enhancements and functional methods based on SDOCT format and concludes with possible directions that this research may take in the near future.

Ionic Mass Transfer Accompanying Anodic Dissolution of Zinc in Alkaline Solution

Holographic interferometry was applied in situ to measure the ionic mass-transfer rates near upward-facing zinc anodes dissolving at high current densities in aqueous KOH solutions. The time-varying interference fringe patterns were converted to individual concentration profiles of , , and ions. The measured ionic concentration profiles agreed well with those predicted by a transient diffusion model for a multicomponent electrolyte. When a zinc anode was electrochemically dissolved in KOH electrolyte, the anode potential abruptly shifted in the noble direction, immediately followed by gas evolution. The onset time for this potential rise and accompanying gas evolution agreed well with the calculated time interval required to drive the ion concentration to zero at the zinc electrode surface. The present model can be applied to not only optimize zinc cell designs but also develop a control method for trouble-free, safe operation of a zinc battery without gas evolution.

Resonant trapping of scattered light in a degenerate resonator

We demonstrate and discuss the formation of an intriguing interference fringe pattern that is visible in stable resonators at resonator lengths corresponding to a higher-order frequency-degeneracy. The optical trajectories that form these fringes are described for arbitrary degeneracy; the fringes can be used to visualize and quantify imaging aberrations of the cavity relative to a cavity consisting of ideal mirrors.

Instantaneous phase-stepping interferometry using polarization imaging with a micro-retarder array

An instantaneous phase-stepping and subsequent phase analysis method, using a CCD camera with a form-birefringent micro-retarder array, is proposed for interferometry. An optical setup of a polarization interferometry using a Twyman-Green interferometer with two polarizers is constructed to analyze the distribution of out-of-plane displacement. Light emerging from the interferometer is recorded using a CCD camera that has micro-retarder array on the CCD plane. This micro-retarder array has four different principal directions. That is, an image obtained by the CCD camera contains four types of data corresponding to four different optical axes of the retarder. The four images separated from the image recorded by the CCD camera are reconstructed using gray-level interpolation. Then, the distributions of the Stokes parameters that represent the state of polarization are calculated from the four images. The phase distribution of the interference fringe pattern produced by the Twyman-Green interferometer is then obtained from these Stokes parameters. This method is applicable to time-dependent phenomena because multiple exposures are unnecessary for sufficient data acquisition in the completion of phase analysis.

Fracture investigation at V-notch tip using coherent gradient sensing (CGS)

Local deformation field and fracture characterization of mode I V-notch tip are studied using coherent gradient sensing (CGS). First, the governing equations that relate to the CGS measurements and the elastic solution at mode I V-notch tip are derived in terms of the stress intensity factor, material constant, notch angle and fringe order. Then, a series of CGS fringe patterns of mode I V-notch are simulated, and the effects of the notch angle on the shape and size of CGS fringe pattern are analyzed. Finally, the local deformation field and fracture characterization of mode I V-notch tip with different V-notch angles are experimentally investigated using three-point-bending specimen via CGS method. The CGS interference fringe patterns obtained from experiments and simulations show a good agreement. The stress intensity factor obtained from CGS measurements shows a good agreement with finite element results under K-dominant assumption.

High-contrast interference pattern of amplified spontaneous emission from dyes under transient grating excitation

We demonstrate a high-contrast interference fringe pattern formed by amplified spontaneous emission (ASE) in a noncollinear two-beam self-diffraction setup by use of dyes. In the presence of a transient grating a stable interference pattern is observed in ASE induced by one- and two-photon absorption. The fringe visibility varies from 0.2 to 0.65 with a temporal delay in the two beams. The variation of the angle between the two exciting beams at the temporal overlap shows an increase in the fringe visibility with an increase in the angle.

Waveform Measurement of Ultra-Short Optical Pulses Based on Two-Photon Absorption in Si-Image Sensor

We demonstrate a novel waveform mesurement system of ultra-short optical pulses based on the two-photon absorption process in a Si-image sensor. Using an interferometer with a tilt mirror in the reference path, the relative time difference between the signal and reference pulses is spatially distributed on the Si-image sensor, so the intensity auto-correlation is monitored as an image at a time without using moving parts. This system can create or remove an interference fringe pattern overlapped on the auto-correlation image by controlling the polarization states of the laser pulse, which is useful for measuring the crossing angle between the signal and reference beams as well as avoiding contamination of the interference fringe into the auto-correlation image. We successfully measured optical pulses less than 100 fs from a fiber ring laser with a temporal resolution of 0.4 fs. The obtained waveform agreed well with that observed with a conventional second harmonic generation (SHG) based auto-correlator.

Residual stress determination and defect detection using electronic speckle pattern interferometry

The paperdeals with the methodology of determining residual stresses using Electronic Speckle Pattern Interferometry (ESPI). ESPI can be used as a truly non-destructive testing technique in that it is a laser-based, optical, full-field, noncontacting method which reveals surface displacements to an accuracy of approximately 300 nm when a helium neon laser is used. In a simple experiment, a fixed-ends rectangular aluminium plate was subjected to uniform loading and the out-of-plane surface displacement field was obtained through ESPI. Subsequently, a comparison of these measurements was made with measurements obtained after the plate was subjected to shot peening. The above method aimed to identify the extent of residual stresses that were imposed on the rectangular plate after the shot peening process, which is known to induce such stress. Bearing in mind that ESPI produces a full-field surface displacement map through a characteristic interference fringe pattern, any anomaly displayed on the fringe pattern could be interpreted as a flaw or defect on or beneath the surface under observation. The authors have included in this paper typical examples where the ESP1, applied in a prototype device constructed by the authors, has identified defects in various engineering components made froth a variety of materials.

Quantum interference in organic solid

We demonstrate high contrast quantum interference between one-photon and three-photon absorption pathways in an organic solid at room temperature. Illumination of a thin polymer film activated with fluorescing dendrimer chromophores of large three photon absorption cross section with two simultaneous femtosecond pulses at near-IR frequency omega and its third harmonic UV frequency 3omega results in a spatial interference fringe pattern observable by eye.

Pulse-laser electroholography by use of interference fringe patterns captured by a CCD

Digital holography is combined with a pulse-laser electroholographic system for a real-time three-dimensional display. Owing to the one-dimensional characteristics of the Bragg-regime acousto-optic spatial-light modulator, vertical parallax cannot be generated from the acoustic signal propagating along the fan-shaped beam direction of the incident laser. To obtain a proper interference pattern, we attach a horizontal slit to the confocal lens system for recording the fringe data, significantly reducing the bandwidth of the vertical fringe data. When the bandwidth-reduced fringe data are displayed by use of a pulse-laser electroholographic system, the clarity and the quality of the image are found to be appreciably improved.

Measurement of Adhesion Force and Elongation of Molecularly Thin Lubricant by Using Transient Response of SPM Cantilever

A novel method for identifying the adhesion force and dynamic elongation of molecularly thin lubricant coated over a DLC (diamond-like-carbon) surface was developed, in which those values were determined through the regression analysis of transient responses of an SPM (scanning probe microscopy) cantilever arising while separating from the target surface. The accuracy of measuring the cantilever displacement was greatly improved by mounting a silicon plate onto the cantilever as an optically reflective surface to produce a high quality image of the interference fringe pattern formed by Michelson interferometry. To analyze experimental transient vibration, a model to describe the separation process was introduced wherein the surface force decreases in proportion to the tip travel distance accompanying lubricant bridging. Based on this model, the adhesion force (contact force) and elongation of the lubricant were measured with varying retracting velocities. The results revealed that the contact force depends slightly on the velocity, and the lubricant elongates by several tens of times’ its original lubricant thickness.

Optical characterization of surfaces by robust reflectance determination based on air-gap interference

In this work we present an optical tool for characterizing the reflectance and polarimetric properties of surfaces. It uses only the image of the interference fringe pattern produced in a thin air-gap between the surface of interest and a glass surface acting as a reference. From only the contrast of the fringe pattern captured with a CCD we may obtain the reflectance of the surface, no need of measuring a reference beam. By taking two images with polarized light, we may get then the polarized reflectance Rp and Rs, but also the ellipsometric magnitude Δ, simply as a phase shift between fringes in p and s polarization. A sample of silicon with a thin layer of thermally grown silica is used to test the method.

Development of a high‐speed laser interferometer using an acousto‐optic deflector

AbstractAn acousto‐optic laser deflector was used as a shutter for high‐speed imaging of laser interference fringes using an ordinary CCD camera. The exposure duration was set by the pulse width of the high‐frequency signal applied to the acousto‐optic deflector. Changes in laser interference fringes due to an impulse discharge in air were obtained at an exposure duration of 4 µs. By applying a sequence of high‐frequency signals with different frequency, the beam was deflected to four different angles at different times, allowing four interference images to be captured on a single video frame. This was used for time‐resolved imaging of the interference fringe pattern. © 2004 Wiley Periodicals, Inc. Electr Eng Jpn, 148(2): 76–83, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20011

Head-Disk Spacing Measurement Using Michelson Laser Interferometry as Observed Through Glass Disk

A spacing measurement using Michelson laser interferometry was developed for measuring the head-disk spacing in a hard disk drive. This method utilizes the phase comparison of two kinds of interference fringe patterns formed respectively over the inner surface of a glass disk and the air bearing surface of a slider through the glass disk. To increase resolution and reproducibility, four principal techniques were newly introduced: an optical system on which a high-definition CCD (charge-coupled device) camera was mounted, external identification of the fringe interval by driving the reference mirror, a wobbling technique to freeze ridgelines at a prescribed position when capturing the fringe image, and a powerful method for extracting ridgelines from the fringe pattern. In this method, the phase shift generated by light reflection on the slider surface incurring multiple beam interference effects must be compensated. For this purpose, first the phase shift was quantified by simulating the multiple beam interferences over a stratified medium inclusive of the lubricating air film, the DLC (diamond-like-carbon) protective layer, the silicon underlayer and the substrate. Then, the shift was subtracted from the optical spacing to obtain the mechanical spacing. Finally, the repeatedly measured mechanical spacings were compared with the theoretically calculated spacings, showing a good accordance between them.

Encoded reference wave security holograms with enhanced features

A simple and cost effective two-step method for making encoded reference wave security holograms with enhanced features, which are readable with an encoded key hologram, has been presented. In the final reading process, two spatially separated sharp focus spots (bright spots) emerge only when the security hologram is illuminated by the decoding, reconstructing beam, generated from the encoded key hologram. In addition these focused spots, upon divergence in the longitudinal direction, further generate variable interferometeric features, i.e. circular and linear interference fringe patterns contained respectively in them. Since the verification/identification pattern in these security holograms are variable interferometric features in addition to the spatially separated sharp focus spots, this type of security hologram is suitable for both visual as well as machine inspection. They can also be used as security codes for better protection against counterfeiting embossed holograms. Recording schemes for the formation of such security holograms and typical experimental results have been presented.