Digital Interferometry Research Articles

Improved visual detection of flaws by using temporal phase modulation in digital speckle shearing interferometry

The visual detection of flaws by digital speckle shearing interferometry is hampered by a spatial texture form cue deteriorated by speckles. The incorporation of time-varying phase modulations, proposed in this letter, adds a temporal component which helps to improve the differentiation of the flaw-developed fringe pattern from its background.

Discrete dynamic resolution considerations in digital speckle correlation interferometry

In digital speckle correlation interferometry, the discrete dynamic resolution of the recording determines the degree of accuracy in deriving the deformation related phase. In this letter, limiting relationships between truncation errors, conditions of saturation, self-interference levels and fringe contrast factors are established in relation with the constraints of this factor.

Automated analysis in digital speckle shearing interferometry using an object step-loading method

Automated analysis in digital speckle shearing interferometry using the conventional two-frame differencing method is hindered by phase unwrapping errors and unresolved fringe patterns due to excessive object load. An object step-loading method with the ability to surmount these limitations is proposed and demonstrated. An added advantage of the proposed method is its ability to yield the entire slope versus load history within one loading cycle.

Phase-correlation techniques for quasi real-time measurement of deformations with digital speckle interferometry

A new approach of in-plane speckle-displacement analysis by binary phase-correlation evaluation is described. An optical implementation of the method based on digital speckle-pattern interferometry and one-focal-length correlator architecture that uses a liquid-crystal light valve is proposed.

Automated linear shear measurements in digital shearing speckle interferometry

This PDF contains the communication on Automated linear shear measurements in digital shearing speckle interferometry.

A digital shearing speckle interferometry technique for modal analysis

Digital shearing speckle interferometry is a laser-based, optical, non-contacting and non-destructive method widely used for the stress and strain analysis of loaded static objects. In this paper, the authors have adapted the technique for whole-field modal analysis. The theoretical basis for this technique is presented and experimental verification is performed on a thin square plate fully constrained and subjected to a steady-state excitation.

Measurement of linear shear in digital shearing speckle interferometry

Errors in measurement of linear shear affect the accuracy of surface strain computations in digital shearing speckle interferometry. A novel method using image processing to measure linear shear is proposed. The method is easy to implement and found to yield fast, consistent and accurate results.

Application of fibre optic digital speckle interferometry to mural painting diagnostics

A fibre optic digital speckle pattern interferometer is reported for mural painting diagnostics. As a result, the influence of flaws and cracks on fringe patterns, characterizing the displacement fields of mural paintings, has been visualized in real time also in an outdoor environment. Preliminary tests establish that this method, by its flexibility and compactness, allows one to overcome some drawbacks of existing conventional arrangements in non-destructive testing of artworks.

Application of Digital Moire Interferometry for Mapping Conical Flows

Digital Moire Interferometry (DMI)—a low cost and sufficiently sensitive geometric interference technique with very low stability requirement analyzed through digital image processing, has been applied to compressible conical flows. An inverse Abel transform algorithm for image reconstruction from moire deflectograms has been developed.

Fizeau digital interferometry with a diffraction-generated spherical wave for testing focusing optics

A sufficiently small, reflective spherical particle at the focus of a test lens can replace the spherical autostigmatizing mirror in Fizeau digital interferometry, which is used for testing focusing optics. This small particle serves as a secondary coherent point source in the test arm and generates by diffraction a spherical wave that is used to produce the test beam. The relationships between the diffraction-generated wave and the size and shape of the diffracting element are discussed and also used to properly select the diffracting element. Experimental results confirm that the new technique has high accuracy.

Digital moire interferometry in experimental analysis of compressible flows

An experimental methodology has been devised to map two-dimensional and axisymmetric flows using principles of Digital Image Processing (DIP) on moire deflectograms obtained on such flows. The integration of DIP and moire interferometry leads to a sufficiently accurate technique-Digital Moire Interferometry (DMI)- which has low stability requirements, is simple to conduct and eliminates the necessity for laborious manual estimation and inaccurate assumptions. An overexpanded axisymmetric jet has been shown mapped using DMI.

A simplified system for digital speckle interferometry

A video speckle interferometer has been demonstrated which uses a spherical surface of small radius at the centre of the camera aperture to simplify the alignment of the reference beam. In combination with a fast microcomputer, this gives a compact and relatively inexpensive system which is able to display phase-stepped interferograms of good quality with a repetition rate approaching one second. The software for phase stepping and unwrapping has novel features and can be applied to other types of interferometer.

Strain measurement by digital speckel interferometry : Maas, A.A.M.; Vrooman, H.A. Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23–28 Apr. 1989, Vol. 2, pp. 594–600. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

Strain measurement by digital speckel interferometry : Maas, A.A.M.; Vrooman, H.A. Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23–28 Apr. 1989, Vol. 2, pp. 594–600. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

Strain measurement by digital speckel interferometry Maas, A.A.M.; Vrooman, H.A. Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23–28 Apr. 1989, Vol. 2, pp. 594–600. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

Strain measurement by digital speckel interferometry Maas, A.A.M.; Vrooman, H.A. Proceedings of the 12th World Conference on Non-Destructive Testing, Amsterdam (Netherlands), 23–28 Apr. 1989, Vol. 2, pp. 594–600. Edited by J. Boogaard and G.M. van Dijk, Elsevier, 1989

Digital phase-shifting interferometry applied to partially developed speckle fields

Partially developed speckle fields produced by a weak scatterer are studied with digital phase-shifting interferometry techniques. Data acquisition and processing is described, and laboratory results are presented

Sensitivity-enhanced electron holography and its application to magnetic recording investigations

The sensitivity for electron-phase measurement in electron holography has been improved to better than 2π/100 by the application of digital interferometry at the optical reconstruction stage. This enables quantitative measurement of magnetic flux as small as (1/100)(h/e)(=4.1×10−17 Wb), hitherto undetectable, with high spatial resolution. With this technique, we have observed the distribution of leakage magnetic field from a thin cross section of a perpendicularly magnetized recording film (cobalt-chromium) with a recording density as high as 300 kFCI (85 nm bit length), the highest density ever directly observed.

A Parallel Fringe-scanning Algorithm for Phase-shifting Interferometry

Abstract In connection with digital interferometry, the evaluation of phase-shifted interferograms can be speeded up by a digital image processor. A special parallel algorithm has been designed for scanning the saw-tooth shaped fringes. It is shown that the number of image passes (TC cycles) for a 2 j × 2 j pixel image is reduced to j instead of 2j. Fringe scanning of a saw-tooth phase image and a pseudocoloured display of the continuous phase is obtained after 1·4s for 512 × 512 points.

Digital phase-stepping interferometry: effects of multiply reflected beams

Les effets des faisceaux reflechis plusieurs fois ne peuvent etre negliges dans un interferometre de Fizeau. Ils peuvent etre minimises par un bon choix de l'algorithme de calcul de phase

Displacement Measurement by Image-processed Speckle Patterns

Abstract The use of a commercial image-processing system in digital speckle-pattern interferometry is demonstrated. The possibilities of electronic-noise suppression and speckle-noise smoothing are discussed. Synthetic speckle patterns have been created and are shown to be useful in software development. Fringe skeletons have been extracted automatically from both synthetic and experimental correlation fringes giving accurate quantitative results.

Digital phase-measuring interferometry with a tunable laser diode

A digital phase-measuring interferometer with a laser-diode source has been developed that is based on a fringe-scanning technique with a stepwise wavelength change by variation of the laser injection current. The phase is changed to produce a relative phase difference between the beams in the two arms of the interferometer. Calibrated phase shifts used for a phase-extraction algorithm are derived from one-dimensional least-squares fits to cosine fringe functions to achieve accurate results. Experimental results are presented.