Speckle Interferometric Techniques Research Articles

Speckle photography and double aperture speckle interferometry using both sides of a suitably designed hololens imaging configuration

In the present work, both sides of a suitably designed hololens imaging configuration have been used in laser speckle photography and double aperture speckle interferometry. A speckle photographic technique has been used to measure in-plane displacement, and a double aperture speckle interferometric technique has been used to measure in-plane displacement component.

High Spatial-Resolution Digital Phase-Stepping Shearography.

Digital phase-stepping shearography is a speckle interferometric technique that uses laser speckles to generate the phase map of the displacement derivatives of a stressed object, and hence can map the stresses of a deformed object directly. Conventional digital phase-stepping shearography relies on the use of video cameras of relatively lower resolution, in the order of 5 megapixels or lower, operating at a video rate. In the present work, we propose a novel method of performing high spatial resolution phase stepping shearography. This method uses a 24 megapixel still digital imaging device (DSLR camera) and a Michelson-type shearing arrangement with an edge-clamped, center-loaded plate. Different phase-stepping algorithms were used, and all successfully generated shearograms. The system enabled extremely high-resolution phase maps to be generated from relatively large deformations applied to the test plate. Quantitative comparison of the maximum achieved spatial resolution is made with the video-rate cameras used in conventional shearography. By switching from conventional (video) imaging methods to still imaging methods, significantly higher spatial resolution (by about 5 times) can be achieved in actual phase-stepping shearography, which is of great usefulness in industrial non-destructive testing (NDT).

High-resolution Imaging Transit Photometry of Kepler-13AB

Abstract Using the high-resolution imaging instrument, ’Alopeke, at the Gemini-N telescope, we obtained simultaneous two-channel time-series observations of the binary exoplanet host star Kepler13-AB. Our optical observations were obtained during a transit event of the exoplanet Kepler-13b and light curves were produced using both speckle interferometric and aperture photometry techniques. Both techniques confirm that the transiting object orbits the star Kepler-13A while different transit depths are seen across the optical wavelength range, being ∼2 times deeper in the blue. These measurements, as well as mass determinations in the literature, are consistent with Kepler-13b being a highly irradiated gas giant with a bloated atmosphere. Our observations highlight the ability of high-resolution speckle imaging to not only assess binarity in exoplanet host stars but robustly determine which of the stars the transiting object actually orbits.

Temporal heterodyne shearing speckle pattern interferometry

Shearing speckle pattern interferometry is a full-field speckle interferometric technique used to determine surface displacement derivatives. In this paper, a new measurement system of real-time heterodyne shearography interferometry is presented. This system combined with heterodyne measurement, shearography interferometry and time domain signal processing technology can dynamically detect the out-of-plane displacement gradient. The principles and system arrangement are described. Using the Jones matrix, the mathematical expression of light intensity distribution passing through this system is deduced. A preliminary experiment was performed to demonstrate the performance of this new device, and simulations were conducted using the finite element method. Comparison of results shows that quantitative measurement of the displacement derivative has been achieved.

ORBITS FOR EIGHTHIPPARCOSDOUBLE STARS

In this paper, we analyze new orbital elements and the quantities that follow from them for eight binaries: WDS 00101+3825 = HDS 23Da,Db, WDS 00321–1218 = HDS 71, WDS 04287+2613 = HDS 576, WDS 04389–1207 = HDS 599, WDS 16206+4535 = HDS 2309, WDS 17155+1052 = HDS 2440, WDS 22161–0705 = HDS 3158, and WDS 23167+3441 = HDS 3315. For seven of them, the orbital elements are calculated for the first time. Binaries, denoted as HDS, were discovered during the Hipparcos mission, and their first observational epoch is 1991.25, the same as the mean epoch of the Hipparcos catalog. We found all other measurements of these binaries in databases. They were obtained in the last 15 yr using the speckle interferometric technique. All studied pairs are close, and all measured separations are less than 0.''4. The resulting orbital periods fall within 26 and 80 yr. In addition to the orbital elements, we also give (O – C) residuals in θ and ρ, masses, dynamical parallaxes, absolute magnitudes, spectral types, and ephemerides for the next 5 yr.

Speckle interferometry of nearby multiple stars. V. 2002–2006 positional measurements

We present the measurements of positional parameters of 194 nearby binary stars performed at the 6-m BTA telescope of the SAO RAS from 2002 through 2006 applying the speckle interferometric technique. The observations were conducted at central filter wavelengths ranging from 545 to 800 nm using a speckle interferometer equipped with a fast CCD and a three-stage image intensifier. A significant part of the observed systems (80 stars) are pairs, the duality of which was discovered or suspected from the Hipparcos satellite observations. The remaining stars are visual binaries and interferometric binary systems with orbital motion period estimates from several to tens of years, as well as the pairs with slow relative motion of the components, used for gaging the image scales and positional angle calibrations.

FOUR FIRST AND TWO RECALCULATED ORBITS FOR BINARIES

In this paper, we analyze new orbital elements, and quantities that can be derived from them, for six binaries. For four of them, WDS 00251+4803 = HDS 56, WDS 01071–0036 = HDS 144 AB, WDS 06426+3955 = HDS 930, and WDS 21014+4037 = HDS 2995, the orbital elements are calculated for the first time. For the other two, WDS 04195+3800 = HDS 552 and WDS 23209+1643 = HEI 88, the orbital elements are recalculated. Five binaries, denoted as HDS, were discovered during the Hipparcos mission while the remaining binary was discovered somewhat earlier. HEI 88 was measured for the first time in 1978. All studied pairs are close, with almost all measured separations less than 0.3 arcsec. For these binaries the observations were usually performed using the speckle-interferometric technique with the exception of HEI 88, which was observed visually on eight occasions. The resulting orbital periods fall within 13 and 69 years. In addition to the orbital elements, we also give (O-C) residuals in θ and ρ, masses, dynamical parallaxes, absolute magnitudes, spectral types, and ephemerides for the next five years.

Differential speckle interferometry: in-depth analysis of the solar photosphere

Aims.We present the results of an experiment performed at the solar telescope THEMIS in 2002 to measure the depth over which the solar granulation extends in the photosphere. Methods: Observations made in the 523.3 nm and 557.6 nm photospheric non-magnetic iron lines were correlated with images in the continuum using spectrograms. The difference in depth between the different levels in the photosphere is projected into a difference of position along the slit of the spectrograph, using a perspective effect similar to the well-known Wilson effect for sunspots. This requires measuring displacements, ones much smaller than the telescope resolution. This is made possible by using a differential speckle interferometric technique, cross-correlating images taken in the continuum and the line. The method is not adapted to following displacements of structures in the core of strong lines, due to their difference in shapes with the structures observed in the continuum. In this case, a sequential cross-spectrum method is developed to cross-correlate images taken at close wavelengths. Results: The raw results are surprising: displacements measured in the blue and the red wings of a line have opposite signs! North and South observations, however, clearly show the expected behavior attributed to a perspective effect. After a description of the observations, we give a first interpretation of the results. The main part of the observed displacement comes from the effect of unresolved Doppler shifts produced by horizontal velocities in the solar photosphere. The perspective effect we seek appears as a second-order term; we find that its amplitude is 2 or 3 times larger than predicted by theoretical 1D models. In the core of strong lines we detect a contrast inversion that also shows up in the cross-correlation function as an anti-correlation peak at line center. Conclusions: .This first use of the differential speckle interferometry technique on the Sun is quite promising for 3D studies at high spatial resolution. Further observations with very good image quality are needed to take advantage of this new technique. THEMIS is operated on the Island of Tenerife by CNRS-CNR in the Spanish Observatorio del Teide of the Instituto de Astrofisica de Canarias.

Digital speckle pattern interferometry for deformation analysis of inner surfaces of cylindrical specimens.

Deformation study of curved engineering and technical surfaces, such as pipes and pressure vessels, has gained much importance in the recent past. Speckle interferometric techniques and their electronic and digital analogs, which are whole field techniques, have been effectively applied for practical nondestructive testing applications over the years. However, little work has been done that discusses the speckle fringe formation with a fruitful theoretical formulation to study deformation analysis of curved surfaces. We propose an extended theory for speckle fringe formation on curved surfaces, which can be applied to the study of curved engineering and technical specimens under various loading conditions such as in-plane, out-of-plane, and out-of-plane shear configurations. Simulated contours are generated by use of finite element models with similar loading conditions, and the data are analyzed and compared with the obtained experimental results.

Improved max-min scanning method for phase determination

We present an improved signal processing algorithm for the max-min scanning method for phase determination in speckle and other interferometric techniques. After recording the intensity changes at one point on the image for a range of arbitrary phase shifts, curve fitting is employed to obtain the intensity waveform corresponding to this position. The phase value is derived from this curve, and the sign of the computed phase angle is determined using the derivative of the fitting curve. The phase map is obtained by performing the same procedure throughout the entire image. This improved algorithm requires neither sorting the recorded image signals nor additional sign images. Experimental examples are provided.

Speckle interferometric technique to assess soap films

An speckle interferometric technique to monitor the thinning process of vertical soap film before the film rupture is presented. The interferometric arrangement consists in a double aperture pupil optical system which images an input diffuser. In a first step, a reference specklegram is stored in the computer buffer memory. Afterwards, the soap film is located in front of one pupil aperture, an uniform displacement of the diffuser is produced and a new speckle pattern is stored. The soap film status is characterized in terms of the changes that this dynamic phase object introduces in the correlation fringes obtained by applying a FFT algorithm to the resulting summed specklegram. This procedure is done in real time as far as the soap film evolves in the successive status. It is experimentally demonstrated that the soap film during drawing acts as a variable wedge. The correlation fringes behavior becomes an important tool to establish the wedge shaped soap film angle and the thickness variations.

A role of fringe pattern catalogue in the course of interferometrically based determination of residual stresses by the hole-drilling method

A further development of the technique for residual stresses determination in thick-walled structures, which is based on a combination of the hole-drilling method and reflection hologram interferometry, is presented. A plane specimen welded from two equal parts of dimensions 130×80 mm 2 in plane and thickness 12 mm is the object of investigation. Weld seam is performed along the shortest side of the specimen. Residual stress field of interest is formed by a superposition of initial welding-induced field and secondary stress field caused by plastic deformation of the specimen. A set of actual fringe patterns, which corresponds to a wide variety of residual stress components both ratio and sign, are reconstructed and presented as illustrations. A series of reference fringe patterns is simulated for the most typical cases inherent in residual stress field under study. It is shown that actual interferograms obtained belong to three main groups depending on a typical form of fringes configuration. On this base the main principles of creating the general catalogue of fringe patterns are established and the first version of this catalogue, which is related to reflection hologram interferometry, is developed. A structure of the catalogue that consists of both actual interferograms and reference fringe patterns is described. Possible ways of further catalogue completing and its direct implementing in the course of quantitative determination of residual stresses are discussed. It is shown that both experimental and numerical data aggregated into the first version of the catalogue can be effectively used for a verification of various coherent optics techniques with respect to a determination of residual stress components by means of hole drilling. An analysis of capabilities of reflection hologram interferometry in the field of residual stresses determination comparing with dual-beam speckle-interferometric techniques is presented. Superimposed residual stress field is quantitatively described in detail for both specimen sides of dimensions 260×80 mm 2. It is shown that fine nuances inherent in residual stress distributions over different specimen faces can be reliably derived from recorded fringe patterns of any type. This study serves as an example of residual stress components determination in real structure with a type of residual stress field to be investigated is unknown before the experiment.

High Spatial Resolution Observations of a Small δ Spot

The Big Bear Solar Observatory (BBSO) has a long tradition of flare observations. In this paper, we would like to direct the reader's attention to observations of a small δ spot that produced a moderate flare activity characterized by 18 C-class and 2 M-class flares. Active region NOAA 8076 (BBSO 3877) was one of the first active regions in the new solar cycle 23. We present for the first time high spatial resolution white-light observations obtained on 1997 August 31 with the speckle masking technique to study mechanisms that trigger flares. Almost diffraction-limited speckle reconstructions revealed the complex and highly dynamical behavior of a small emerging δ configuration in the central part of NOAA 8076. We found strong shear flows and indications of strong transverse fields in the small δ spot. The flare-producing mechanism for this small activity complex was very similar to that of the outstanding flare-producing region NOAA 5395 of 1989 March however, on a completely opposite spatial scale. As an important by-product, the speckle-interferometric techniques provided information about the seeing quality at a site. We used the spectral ratio technique to estimate the Fried parameter r0. We measured a maximum Fried parameter of r=10.3 cm and an average Fried parameter of r0 = 9.0 ± 0.7 cm in which the standard deviation reflects the temporal variations of the seeing, indicating good seeing conditions during our observations.

New Digital Magnetograph at Big Bear Solar Observatory

A new digital magnetograph system has been installed and tested at Big Bear Solar Observatory. The system uses part of BBSO's existing videomagnetograph (VMG) system: a quarter wave plate, a ferro-electric liquid crystal to switch polarizations, and a 0.25 A bandpass Zeiss filter tuned at Ca i 6103 A. A new 256×256 pixels, 12-bit Dalsa camera is used as the detector and as the driver to switch the liquid crystal. The data rate of the camera is 90 frames s−1. The camera is interfaced to a Pentium-166 PC with a μTech imaging board for data acquisition and analysis. The computer has 128 MByte of RAM, and up to 700 live images can be stored in memory for quick post-exposure image processing (image selection and alignment). We have significantly improved the sensitivity and spatial resolution over the old BBSO VMG system. In particular: (1) New digital image data are in 12 bits while the video signal is digitized as 8 bits. Polarizations weaker than 1% can not be detected by a single pair subtraction in the video system. The digital system can detect a polarization signal of about 0.3% by a single pair subtraction. (2) Data rate of the digital system is 90 frames s−1, that of the video system is 30 frames s−1. So the time difference between two polarizations is reduced in the new system. Under good seeing conditions, the data rate of 90 frames s−1 ensures that most of the wavefront distortions are ‘frozen’ and fairly closely the same for the left and right circular polarized image pairs. (3) Magnetograms are constructed after image selection and alignment. We discuss the characteristics of this new system. We present the results of our first tests to reconstruct magnetograms with speckle interferometric techniques. We also present some preliminary results on the comparison of facular/micropore contrasts and magnetic field structure. The experiment with this small detector lays ground for a larger format digital magnetograph system at BBSO, as well as a future Fabry-Perot system, which will be able to scan across the spectral line.

Comparative measurement by speckle interferometry using holographically reconstructed master object

In this paper a new comparative speckle interferometric technique is presented: we call it the difference digital speckle pattern interferometric (DDSPI) method. The technique uses the two holographically reconstructed virtual images of the (unloaded and loaded) master object as references to detect the difference in displacement profiles of two macroscopically similar but microscopically different object surfaces. The two images corresponding to the two different states of the master object are recorded holographically on one holographic plate or on a thermoplastic film. So, the method does not require the real presence of the master object in the comparison process: the master object does not need to be subjected to repeated stresses, and each test object can be compared with the very same two states of the master object, which makes the method more precise and faster than conventional techniques.

Robust procedure for fringe analysis

A robust procedure for analyzing fringe patterns obtained from speckle interferometric techniques is proposed. The fringes generally are observed only in a region S of a rectangular lattice L. We give a method for computing (from S) the region R, where the unwrapped phase is to be computed; this computation is done by use of a morphological filter (in particular, a closing filter). We then use a fast-unwrapping algorithm to compute the phase: a preconditioned conjugate-gradient algorithm that uses the discrete Fourier transform.

Effects of laser stroke parameters on quantitative vibration measurements with stroboscopic shearography

Digital shearography is a full-field speckle interferometric technique similar to electronic holography. Traditionally, shearography and holography have been used for vibration measurement with either time averaged or stroboscopic techniques. Time averaging images sinusoidal motion of an object’s surface over many periods of vibration, resulting in a fringe pattern representative of the magnitude of the displacement mode shape. Stroboscopic illumination synchronizes short bursts, or strokes, of laser light with extrema of vibration. This essentially freezes motion of the vibrating surface, allowing it to be studied with techniques normally reserved for static deformation. In particular, phase stepping, an established technique for capturing a series of images and calculating the exact displacement at every point, can be applied to vibration measurement. If displacement amplitudes calculated from laser strobing and phase stepping are to be used for measurement of peak vibration response, corrections are necessary to compensate for errors due to the finite duration of the laser strokes as well as their improper timing due to system impedance. In this presentation, effects of stroke duration will be expressed mathematically and trends demonstrated experimentally. Potential solutions for stroke offset correction will be discussed and experimental validation provided. [Work sponsored by the PSU Applied Research Laboratory.]

Shape Control of an Adaptive Mirror at Different Angles of Inclination

The topic of this paper is the quasi-static shape control of an adaptive mirror, which is deformed due to gravity at different angles of inclination. Next to the basic design aspects of the adaptive mirror, a comparison between the numerical and experimental results is presented. Special emphasis is given to the description of the experimental setup for the verification of the shape control. Since for this structure the gravity-induced deformations are in the order of micrometers, a speckle interferometric measurement system and phase-shifting techniques have been used. The experimental data obtained with respect to the out-of-plane displacement of the mirror confirm the results of the numerical simulations. Moreover, the efficiency of the shape control is investigated and a correction scheme is presented.

The infrared morphology of young stellar objects without companions - A speckle interferometric study

view Abstract Citations (10) References (51) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Infrared Morphology of Young Stellar Objects Without Companions: A Speckle Interferometric Study Dewarf, L. E. ; Dyck, H. M. Abstract 1D speckle interferometric techniques are employed in the NIR wavelength range of 1.25 to 4.8 microns to ascertain the morphology of 18 young stellar objects not known to have associated companions. We find that three of these objects are resolved as core/halo distributions or are partially resolved with a high level of confidence. Five other sources probably show some structure although the confidence level is lower. The ten remaining sources either show evidence for very small angular scale structure or are unresolved with an upper limit of about 0.2 arcsec. Our results are compared to other published angular size data. A relationship between the 12 to 25 micron spectral slope and the physical extent of the material in the near infrared is discovered and compared to simple models. We interpret this relationship as an indication that the effective scale size of circumstellar matter surrounding young stellar objects decreases with advancing age. Publication: The Astronomical Journal Pub Date: June 1993 DOI: 10.1086/116599 Bibcode: 1993AJ....105.2211D Keywords: Infrared Astronomy; Protostars; Speckle Interferometry; Stellar Envelopes; Accretion Disks; Star Formation; Astrophysics; INFRARED: STARS; STARS: IMAGING; STARS: PRE-MAIN SEQUENCE full text sources ADS | data products SIMBAD (24)

Small-Scale Structures in Active Regions

AbstractWithin the last few years significant progress has been made in our understanding of the small-scale structures in active regions. Here I present some of the newest findings obtained by using speckle interferometric techniques. There exist continuum bright points with a contrast of about 30% that are cospatial with strong magnetic fields. The observations are consistent with the assumption that some facular and network bright points are the white-light signature of magnetic fluxtubes with a diameter of about 200 km. Magnetic elements larger than about 300 km are mainly darker than the average quiet sun. Their properties are similar to what has been called magnetic knots or invisible sunspots. In highly magnetic areas there is no clear relationship between continuum intensity and magnetogram signal at the smallest spatial scales. The magnetic field of pores extends beyond the dark umbra. There radially elongated structures may appear that are similar to penumbral filaments in sunspots.