Showing papers on "Speckle imaging published in 1998"

ICCD Speckle Observations of Binary Stars. XIX. An Astrometric/Spectroscopic Survey of O Stars

Abstract: We present the results of a speckle interferometric survey made with the CHARA speckle camera and 4 m–class telescopes of Galactic O-type stars with V 59% have a visual or spectroscopic companion) but less so among field and especially runaway stars. There are many triple systems among the speckle binaries, and we discuss their possible role in the ejection of stars from clusters. The period distribution of the binaries is bimodal in log P, but we suggest that binaries with periods of years and decades may eventually be found to fill the gap. The mass ratio distribution of the visual binaries increases toward lower mass ratios, but low mass ratio companions are rare among close, spectroscopic binaries (probably because of the difficulty of spectroscopic detection rather than a real deficit). We present distributions of the eccentricity and longitude of periastron for spectroscopic binaries with elliptical orbits, and we find strong evidence of a bias in the longitude of periastron distribution (the Barr effect), which is probably caused by line distortions introduced by circumstellar gas.

Speckle interferometry with temporal phase evaluation for measuring large-object deformation

Abstract: We propose a new method for measuring large-object deformations by using temporal evolution of the speckles in speckle interferometry. The principle of the method is that by deforming the object continuously, one obtains fluctuations in the intensity of the speckle. A large number of frames of the object motion are collected to be analyzed later. The phase data for whole-object deformation are then retrieved by inverse Fourier transformation of a filtered spectrum obtained by Fourier transformation of the signal. With this method one is capable of measuring deformations of more than 100 μm, which is not possible using conventional electronic speckle pattern interferometry. We discuss the underlying principle of the method and the results of the experiments. Some nondestructive testing results are also presented.

Automated fringe pattern analysis in experimental mechanics: A review

Abstract: The paper reviews the main numerical techniques that have been developed to carry out fully automated analysis of fringe patterns resulting from solid mechanics experiments. These include temporal and spatial phase shifting interferometry, temporal and spatial phase unwrapping, and calculation of strain fields from the phase maps. Systematic and random errors associated with the various procedures are also analysed. A unified treatment for both speckle and smooth-wavefront interferograms is presented, and the common features underlying many of the algorithms are emphasized. The paper is illustrated with applications that include ball impact (moire photography), bending waves in orthotropic plates (double-pulsed dual-reference wave holography) and finite strains in propellant grains (fine grid technique).

Large in-plane displacement measurement in dual-beam speckle interferometry using temporal phase measurement

Abstract: Measurement of in-plane displacements of a diffuse object by observing the temporal fluctuation of the speckle pattern in a dual-beam illumination speckle interferometer is illustrated. To conceive the temporal changes the object is displaced in its plane continuously. A high-speed camera is used to acquire a number of frames of the image of the object motion sequentially. Through Fourier transformation and inverse Fourier transformation of the frames stacked together, the total phase is determined. Finally, the magnitude of the in-plane displacement of the object motion is extracted. The range of displacement that can be measured using this novel method lies between few microns and over 100 μm on the upper end. Theory together with experimental results are presented in this paper.

Young's modulus of thin films by speckle interferometry

Abstract: Speckle interferometry has been applied to the measurement of Young's modulus in thin films. The present study has two novel aspects: the specimens used were approximately 1 m thick and less than 1 mm long, so the speckle images were obtained by photomicroscopy; and the digital images were analysed by quantitative treatment at intense speckles, rather than by the more standard techniques. Displacements and strains within the gauge length were obtained with low statistical uncertainties. Young's modulus values for three varieties of copper thin films were obtained. All were lower than the polycrystalline bulk average value and the electrodeposited film's modulus was lower than those of both the vapour-deposited films.

Novel temporal fourier transform speckle pattern shearing interferometer

Abstract: A method to measure the derivative of displacement using time variation changes in the object together with Fourier transform analysis in speckle shear interferometry is presented. The concept of the method is that the object is deformed continuously and a large number of sheared images of the object motion are acquired using a high speed CCD camera. The derivative of the object deformation is then retrieved from this large set of data using Fourier transformation. The method is capable of obtaining information for object displacements over 500 µm, which is a very difficult task when using conventional electronic speckle pattern shearing interferometry. Theory as well as some of the experimental results with the new method are delineated.

Dynamic laser speckle in complex ABCD optical systems

Abstract: Within the framework of ABCD matrix theory an exact analytical expression is derived for the space–time-lagged photocurrent covariance that is valid for arbitrary (complex) ABCD optical systems, i.e., systems that include Gaussian-shaped apertures and partially developed speckle. General expressions are derived for the mean spot size and both the mean speckle size and the temporal coherence length. Additionally, a general description of both speckle boiling and speckle translation in an arbitrary observation plane is given. Included in the analysis is the effect of a finite wave-front-curvature radius for the Gaussian-shaped laser beam illumination of the target. The effects of diffraction and wave-front-curvature radius are discussed for both imaging systems and a Fourier transform system. It is shown that, whereas diffraction affects the speckle dynamics in both cases, a finite wave-front curvature affects only the speckle dynamics in the Fourier transform system. Further, the effects of finite detector apertures are considered, in which the effects of speckle averaging are included and discussed. In contrast to previous work, the obtained analytical results are expressed in a relatively compact form yet fully contain all diffraction effects and apply to an arbitrary ABCD optical system.

Fiber electronic speckle pattern interferometry and its applications in residual stress measurements.

Abstract: A two-dimensional in-plane displacement-sensitive electronic speckle pattern interferometer has been developed. With a fiber coupler with one input and four outputs, two sets of dual-beam interferometric configurations in orthogonal directions are constructed to determine in-plane displacements completely. When a CCD camera with a zoom lens is located at an adequate distance from the specimen, a testing area ranging from 1.4 mm × 1.0 mm to 30.0 mm × 24.0 mm can be examined in quasi-real-time. Incorporated with the hole-drilling technique, it has currently been demonstrated in residual stress measurements. One application is for determining the residual stress of a thick cylinder consisting of two concentric circular tubes with interference fit. The other is for analyzing the residual stress distribution of a recordable optical compact disc. A simple approach to interpreting the values of residual stresses from the displacement contours is presented.

Laser-speckle angular-displacement sensor: theoretical and experimental study

Abstract: A novel, to our knowledge, method for the measurement of angular displacement for arbitrarily shaped objects is presented in which the angular displacement is perpendicular to the optical axis. The method is based on Fourier-transforming the scattered field from a single laser beam that illuminates the target. The angular distribution of the light field at the target is linearly mapped on a linear image sensor placed in the Fourier plane. Measuring this displacement facilitates the determination of the angular displacement of the target. It is demonstrated both theoretically and experimentally that the angular-displacement sensor is insensitive to object shape and target distance if the linear image sensor is placed in the Fourier plane. A straightforward procedure for positioning the image sensor in the Fourier plane is presented. Any transverse or longitudinal movement of the target will give rise to partial speckle decorrelation, but it will not affect the angular measurement. Furthermore, any change in the illuminating wavelength will not affect the angular measurements. Theoretically and experimentally it is shown that the method has a resolution of 0.3 mdeg (≈5 μrad) for small angular displacements, and methods for further improvement in resolution is discussed. No special surface treatment is required for surfaces giving rise to fully developed speckle. The effect of partially developed speckle is considered both theoretically and experimentally.

Fluorescent speckle microscopy of spindle microtubule assembly and motility in living cells.

Abstract: Publisher Summary This chapter introduces the principles of the fluorescent speckle microscopy method for microtubules, and then briefly describes the features of a digital imaging system that are important for speckle image recording and analysis with other optical modes, such as phase contrast or vital staining, with DNA dyes such as the blue fluorescent Hoescht or DAPI to record chromosome position. Applications of the method are presented for measuring microtubule movements in tissue cell spindles and asters and in spindles reassembled in vitro in cytoplasmic extracts of Xenopus eggs. A high-resolution, multimode, multiwavelength, digital fluorescence light microscope is used for fluorescence imaging of mitosis in living cells or cytoplasmic extracts that have enough sensitivity for fluorescence speckle imaging. Images of chromosomes and cell structure can also be obtained by transmitted light differential interference contrast (DIC) or phase contrast. The microscope utilizes conventional wide field optics and a cooled, slow-scan CCD camera for image detection.

Measurement of transient deformations with dual-pulse addition electronic speckle-pattern interferometry

Abstract: We describe an electronic speckle-pattern interferometry system for analyzing addition fringes generated by the transient deformation of a test object. The system is based on a frequency-doubled twin Nd:YAG laser emitting dual pulses at a TV camera field rate (50 Hz). The main advance has been the automatic, quantitative analysis of dual-pulse addition electronic speckle-pattern interferometry data by the introduction of carrier fringes and the application of Fourier methods. The carrier fringes are introduced between dual pulses by a rotating mirror that tilts the reference beam. The resulting deformation-modulated addition fringes are enhanced with a deviation filter, giving fringe visibility close to that of subtraction fringes. The phase distribution is evaluated with a Fourier-transform method with bandpass filtering. From the wrapped phase distribution, a continuous phase map is reconstructed with an iterative weighted least-squares unwrapper. Preliminary results for a thin plate excited by an acoustic shock show the suitability of the system for the quantitative evaluation of transient deformation fields.

Shape Measurement by use of Temporal Fourier transformation in Dual-Beam Illumination Speckle Interferometry

Abstract: We outline a novel method for determining the shape of an object by use of temporal Fourier-transform analysis in dual-beam illumination speckle interferometry. The object whose shape is to be determined is rotated about an axis, and a number of frames of the image of the object motion are acquired. Temporal in-plane displacement that is due to the object rotation is related to the shape of the object and is retrieved from this large set of data by Fourier transformation. With this method one can determine the absolute height of the object with variable resolution, thereby allowing shapes of objects with large and small slopes to be determined. The theory of the method along with experimental results is presented.

Asymmetric iterative blind deconvolution of multiframe images

Abstract: Imaging through a stochastically varying distorting medium, such as a turbulent atmosphere, requires multiple short-exposure frames to ensure maximum resolution of object features. Restoration methods are used to extract the common underlying object from the speckle images, and blind deconvolution techniques are required as typically there is little prior information available about either the image or individual PSFs. A method is presented for multiframe restoration based on iterative blind deconvolution, which alternates between restoring the image and PSF estimates. A maximum-likelihood approach is employed via the Richardson-Lucy (RL) method which automatically ensures positively and conservation of the total number of photons. The restoration is accelerated by applying a vector sequence is treated as a 3D volume of data and processed to produce a 3D stack of PSFs and a single 2D image of the object. The problem of convergence to an undesirable solution, such as a delta function, is addressed by weighting the number of image or PSF iterations according to how quickly each is converging, this leads to the asymmetrical nature of the algorithm. Noise artifacts are suppressed by using a dampened RL algorithm to prevent over fitting of the corrupted data. Results are presented for real single frame and simulated multiframe speckle imaging.

Transient deformation analysis by a carrier method of pulsed electronic speckle-shearing pattern interferometry.

Abstract: The introduction of a pulsed laser into an electronic speckle-shearing pattern interferometer allows high-speed transient deformations to be measured. We report on a computerized system that permits automatic data reduction by introducing carrier fringes through the translation of a diverging lens. The quantitative determination of the phase map that is due to deformation is carried out by the spatial synchronous detection method. Experimental results obtained for a metal plate transiently deformed by an electromagnetic hammer illustrate the advantages of the proposed system.

Speckle Masking Imaging of Sunspots and Pores

Abstract: In recent years, speckle interferometry has been successfully applied to various solar phenomena and provides a powerful tool to study solar small-scale structures. The present investigation lays special emphasis on sunspots and sunspot pores. The observations have been performed with the Vacuum Tower Telescope (VTT) at the Observatorio del Teide (Tenerife) in the years from 1992 to 1994. Time series of high-spatial-resolution observations reveal the highly dynamical evolution of sunspot fine structures such as umbral dots, penumbral grains or the small-scale brightenings in the vicinity of sunspots observed in the wings of strong chromospheric absorption lines (moustache phenomenon). The reconstructed images show small-scale structures close to the telescopic diffraction limit of 0.16″ at 550 nm. Furthermore, the high transmission of a Fabry–Perot interferometer (FPI) as the principal optical element of a two-dimensional spectrometer allows one to reconstruct directly images taken within a passband of 0.014 nm.

The 'Pisco' Speckle Camera at Pic Du Midi Observatory

Abstract: We present a new speckle camera designed and built at Observatoire Midi-Pyrenees. This focal instrument has been used for four years with the 2-meter Bernard Lyot Telescope of Pic du Midi observatory. It can be set in various operating modes: full pupil imaging, masked-pupil imaging, spectroscopy, wave-front sensor and stellar coronagraphy, hence its name 'PISCO' ('Pupil Interferometry Speckle COronagraph'). Restored images of double and triple stars have demonstrated its capabilities in providing close to diffraction limited images (0.06′′ in V). PISCO has been fully tested and is now ready to be used by the whole astronomical community.

Unwrapping of digital speckle-pattern interferometry phase maps by use of a minimum L 0 -norm algorithm

Abstract: The performance of a minimum L0-norm unwrapping algorithm is investigated by use of synthetic digital speckle-pattern interferometry (DSPI) wrapped phase maps that simulate experimentally obtained data. This algorithm estimates its own weights to mask inconsistent pixels. Particular features usually included in DSPI wrapped phase distributions, such as shears, speckle noise, fringe cuts, object physical limits, and superimposed phase maps, are analyzed. Some adequate approaches to solving these features are discussed. Finally, it is shown that a complex case in which shears and fringe cuts coexist in the wrapped phase cannot be solved satisfactorily with the minimum L0-norm algorithm by itself. To cope with this problem, we propose a new scheme.

Roughness parameters and surface deformation measured by coherence radar

Abstract: The 'coherence radar' was introduced as a method to measure the topology of optically rough surfaces. The basic principle is white light interferometry in individual speckles. We will discuss the potentials and limitations of the coherence radar to measure the microtopology, the roughness parameters, and the out of plane deformation of smooth and rough object surfaces. We have to distinguish objects with optically smooth (polished) surfaces and with optically rough surfaces. Measurements at polished surfaces with simple shapes (flats, spheres) are the domain of classical interferometry. We demonstrate new methods to evaluate white light interferograms and compare them to the standard Fourier evaluation. We achieve standard deviations of the measured signals of a few nanometers. We further demonstrate that we can determine the roughness parameters of a surface by the coherence radar. We use principally two approaches: with very high aperture the surface topology is laterally resolved. From the data we determine the roughness parameters according to standardized evaluation procedures, and compare them with mechanically acquired data. The second approach is by low aperture observation (unresolved topology). Here the coherence radar supplies a statistical distance signal from which we can determine the standard deviation of the surface height variations. We will further discuss a new method to measure the deformation of optically rough surfaces, based on the coherence radar. Unless than with standard speckle interferometry, the new method displays absolute deformation. For small out-of-plane deformation (correlated speckle), the potential sensitivity is in the nanometer regime. Large deformations (uncorrelated speckle) can be measured with an uncertainty equal to the surface roughness.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Acoustically modulated speckle imaging of biological tissues.

Abstract: A video laser speckle imaging technique yields images with contrast based on the mechanical properties of a tissue. Fluctuations of laser speckle patterns induced by acoustically driving the tissue at various frequencies in the 0–30-Hz range encode the mechanical strain of the tissue. At each acoustic frequency and within the camera acquisition time, each camera pixel integrates a temporally fluctuating speckle intensity whose variance encodes the mechanical strain in response to the acoustic modulation. The magnitude and the frequency dependence of this strain provide mechanical information about the tissue and are the contrast mechanism for images.

Digital speckle interferometry: some developments and applications for vibration measurement in the automotive industry

Abstract: This paper presents an overview of some recent progress in digital speckle interferometry and its application for vibration measurement in the automotive industry. It describes three methods to generate raw vibration fringe patterns with better quality; provides speckle averaging, phase shifting, and phase reconstruction iteration procedures to produce a high-quality and noise-free fringe pattern; illustrates one single setup for measuring both vibration deformation and geometric shape of an object; and demonstrates how powerful this tool is for whole vehicle modal survey, interactive design optimization, CAE model correlation, and nondestructive testing. Finally, areas for further development are suggested.

Complex division as a common basis for calculating phase differences in electronic speckle pattern interferometry in one step.

Abstract: We point out that all formulas for calculating the phase map of object deformations in one step can be described by the same simple formalism of a complex division.

Speckle Interferometry at the US Naval Observatory

Abstract: We present speckle interferometer measurements of 467 binary stars taken at the US Naval Observatory in Washington, DC, using the 66 cm refractor, from 1990 October through 1992 December. The observing program is designed to provide high-quality observations of binaries in the 03-35 range of separations and as faint as 10.0 mag. More than 8000 measurements have been made to date, of which we report the results for 2329. Not only is it our intent to provide accurate data for interesting binary stars, but also, by careful calibration, to firmly relate the \"classical\" astrometry of binary stars to that being obtained today by speckle and that which will soon be obtained by other modern techniques such as long-baseline optical interferometry.

Coherence-Domain Methods in Tissue and Cell Optics

Abstract: Effects that accompany the propagation of laser radiation in tissues and interaction of laser radiation with cell flows are considered. These effects include diffraction, formation of speckle structures, interference of speckle fields, scattering from moving particles, etc. We discuss coherent optical methods that hold much promise for applications in biomedicine, such as photon-correlation spectroscopy; speckle interferometry; coherent topography and tomography; diffusion wave spectroscopy; phase, confocal, and Doppler microscopy; and low-coherence interferometry and tomography.

Statistical theory of two-wave speckle interferometry and its application to the optimization of deformation measurements

Abstract: These Ecole polytechnique federale de Lausanne EPFL, n° 1797 (1998) Reference doi:10.5075/epfl-thesis-1797Print copy in library catalog Record created on 2005-03-16, modified on 2016-08-08

Optical configuration in speckle shear interferometry for slope change contouring with a twofold increase in sensitivity

Abstract: We present a novel optical configuration that yields a fringe pattern that represents the slope changes of a three-dimensional object with a twofold increase in sensitivity. The method offers controllable sensitivity over a wide range. We accomplish it by modifying the in-plane displacement sensitive configuration of speckle interferometry. The detailed theory and the experimental results are presented with a brief discussion on the limiting aspects of the configuration.