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  • 1.
    Benckert, Lars
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Jonsson, Mikael
    Molin, Nils-Erik
    Measuring true in-plane displacements of a surface by stereoscopic white-light speckle photography1987In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 26, no 2, p. 167-169Article in journal (Refereed)
    Abstract [en]

    When in-plane surface deformations are measured using white-light speckle photography, errors arise if an out-of-plane displacement is present. Stereoscopic photography resolves this problem and makes possible the measurement of true in-plane displacements. A rigid-body translation is introduced to determine unambiguously the direction of the displacement

  • 2.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Michael, Fergusson
    Viospatia AB.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Virtual projective shape matching in targetless CAD-based close-range photogrammetry for efficient estimation of specific deviations2018In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 57, no 5, article id 053110Article in journal (Refereed)
    Abstract [en]

    A concept for targetless, computer-aided design (CAD)-based, close-range photogrammetry for online shape inspection is introduced. The shape of an object, which is arbitrarily located on a conveyor belt, is to be measured and compared with its nominal shape as defined by a CAD model. For most manufactured objects, deviations are only measured at a few given comparison points. These deviations can be estimated using local photogrammetry based on a priori geometrical information given by the CAD model and the comparison points. Our method results in faster output with higher precision, because we do not generate a shape representation of the entire measured object using typical photogrammetric methods. Images depicting the object from convergent angles are captured by an array of cameras in a precalibrated network, and the CAD model is matched and aligned, within the projective geometry of the camera network, to the depicted object in the images without the use of targets. An algorithm for solving this virtual projective targetless shape matching problem is presented.

  • 3.
    Bergström, Per
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Mathematical Science.
    Rosendahl, Sara
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Shape verification using dual-wavelength holographic interferometry2011In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 50, no 10, article id 101503Article in journal (Refereed)
    Abstract [en]

    In automotive industry there is an interest of controlling the shape of a large number of identical components on-line in the manufacturing process. We propose a method to do this by capturing a digital hologram of the object and then using information from its computer aided design (CAD) model to calculate the shape and determine the agreement between the manufactured object and the CAD-model. The holographic recording of the object is done using dual wavelengths with a synthetic wavelength of approximately 400 μm. The optical measurement results in a wrapped phase map with the phase values in the interval [−π, π]. Each phase interval represents a depth distance on the object of about 0.2 mm. The phase unwrapping is done iteratively using information from the CADmodel. This implies that it is possible to measure large discontinuities on the surface of the measured object. The method also gives a point-to-point correspondence between the measurement and the CAD-model which is vital for tolerance control.

  • 4.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    New high-speed photography technique for observation of fluid flow in laser welding2010In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 49, no 10Article in journal (Refereed)
    Abstract [en]

    Recent developments in digital high-speed photography allow us to directly observe the surface topology and flow conditions of the melt surface inside a laser evaporated capillary. Such capillaries (known as keyholes) are a central feature of deep penetration laser welding. For the first time, it can be confirmed that the liquid capillary surface has a rippled, complex topology, indicative of subsurface turbulent flow. Manipulation of the raw data also provides quantitative measurements of the vertical fluid flow from the top to the bottom of the keyhole.

  • 5.
    Eriksson, Ingemar
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Haglund, Peter
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Powell, John
    Luleå University of Technology, Department of Engineering Sciences and Mathematics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Holographic measurement of thermal distortion during laser spot welding2012In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 51, no 3Article in journal (Refereed)
    Abstract [en]

    Welding distortion is an important engineering topic for simulation and modeling, and there is a need for experimental verification of such models by experimental studies. High-speed pulsed digital holography is proposed as a measurement technique for out-of-plane welding distortion. To demonstrate the capability of this technique, measurements from a laser spot weld are presented. A complete twodimensional deformation map with submicrometer accuracy was acquired at a rate of 1000 measurements per second. From this map, particular points of interest can be extracted for analysis of the temporal development of the final distortion geometry.

  • 6.
    Fredriksson, Håkan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Hyyppä, Kalevi
    Multisource flash system for retroreflective beacon detection in CMOS cameras2008In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 47, p. 103001-Article in journal (Refereed)
    Abstract [en]

    We present a method for improving a flash system for retroreflective beacon detection in CMOS cameras. Generally, flash systems are designed in such a manner that makes them suited for beacon detection in a small range interval. We strive to increase the flash system range interval by exploiting the directional properties of the retroreflector. Thus, light sources placed relatively far away from the optical axis of the camera will contribute only when the retroreflector is far away. This fact can be used to compensate for the 1/distance2 dependency of optical power. We present underlying theory and formulae, then describe a flash system consisting of several light-emitting diodes that was designed by considering the presented method. Simulations show that the usable flash range of the improved system can be almost doubled compared to a general flash system. Tests were performed indicating that the presented method works according to theory and simulations.

  • 7.
    Hyyppä, Kalevi
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Signal response of a laser beam scanner1994In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 33, no 8, p. 2770-2776Article in journal (Refereed)
  • 8.
    Kaplan, Alexander
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Product and Production Development.
    Analysis and modeling of a high-power Yb:fiber laser beam profile2011In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 50, no 5Article in journal (Refereed)
    Abstract [en]

    Recently the fiber and the disk laser have been developed as advanced high power lasers of continuous wave type. Their beams are fiber-guided. Their low beam parameter product determines the focused beam as a high power density tool for laser materials processing. The lateral and axial power density distribution is crucial for the process. The measurement of a focused Yb:fiber laser beam is compared with its theoretical profile. While a Gauss beam describes the real beam in the far field, in the vicinity of the focus the beam is similar to a top-hat profile. In particular, the peak power density is lower around the focus than for a Gaussian beam. This provides a flatter, less varying optical tool along a certain axial range. A suitable model of the focused laser beam is achieved by superposition of a Gauss beam with a second but negative Gauss beam, each with matched parameters for power, spot diameter, and Rayleigh length. Owing to its much better accuracy with less than a 20% error, the model beam is applicable, e. g., for simulation of the welding process

  • 9.
    Khodadad, Davood
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Hällstig, Emil
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Dual-wavelength digital holographic shape measurement using speckle movements and phase gradients2013In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 52, no 10, article id 101912Article in journal (Refereed)
    Abstract [en]

    A new method to measure shape by analyzing the speckle movements in images generated by numerical propagation from dual-wavelength holograms is presented. The relationship of the speckle movements at different focal distances is formulated, and it is shown how this carries information about the surface position as well as the local slope of the object. It is experimentally verified that dual-wavelength holography and numerically generated speckle images can be used together with digital speckle correlation to retrieve the object shape. From a measurement on a cylindrical test object, the method is demonstrated to have a random error in the order of a few micrometers.

  • 10.
    Marklund, Olov
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Huntley, Jonathan M.
    Wolfson School of Mechanical and Manufacturing Engineering, Loughborough University.
    Cusack, Rhodri
    MRC Cognition and Brain Sciences Unit, 15 Chaucer Road, Cambridge.
    Robust unwrapping algorithm for three-dimensional phase volumes of arbitrary shape containing knotted phase singularity loops2007In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 46, no 8Article in journal (Refereed)
    Abstract [en]

    The extension of path-independent 2-D phase unwrapping algorithms, based on placement of branch cut lines between phase singularities of opposite sign, was recently proposed for phase volumes in a paper by Huntley. In 3-D, the singularities were shown to form closed loops, and path independence was achieved by placing branch cut surfaces across the loops. In the current work, we describe in detail an optimized and extended version of Huntley's algorithm. It deals in particular with two aspects that are essential for practical phase volumes: 1. how to close partial loops that pass through arbitrary boundaries separating valid and invalid phase data, and 2. how to select the set of loops having the shortest length. The second algorithm is necessary to deal with ambiguous cases that can arise when the singularities form knots, i. e., two loops pass through a single phase volume element. The performance of the algorithm is demonstrated on 3-D phase maps from two types of medical imaging data: medical resonance imaging (MRI) and x-ray interferometry.

  • 11.
    Melin, L. Gunnar
    Luleå tekniska universitet.
    High-speed moire photography for studying dynamic properties in carbon fiber composites1998In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 37, no 2, p. 642-649Article in journal (Refereed)
    Abstract [en]

    In the experiments reported here, a moire technique for measuring in-plane displacements was applied to the study of carbon/epoxy composite specimens deformed at high strain rates. The moire fringes were analyzed using the Fourier transform method. The measurements show that the material behaves in a linearly elastic manner up to fracture. Crack propagation rates of about 2000 m/s in the grating plane were observed. The optical aspects of the experiment are discussed

  • 12.
    Mohan, N.K.
    et al.
    Indian Institute of Technology.
    Svanbro, Angelica
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Molin, Nils-Erik
    Dual-beam symmetric illumination-observation TV holography system for measurements2001In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 40, no 12, p. 2780-2787Article in journal (Refereed)
    Abstract [en]

    The Leendertz dual-beam symmetric illumination-normal observation arrangement is widely employed for real time evaluation of in-plane displacement components as well as surface shape. Instead of observing along the optical axis, we have examined the Leendertz arrangement by observing the scattered light along the direction of the illumination beams, and imaged it as two separate images onto the photo sensor of a CCD camera. The interferometer is a combination of two channels, each of which measures independently and simultaneously the information pertaining to either the in-plane displacement component of a deformation vector, or the surface relief variation of a three-dimensional object. In addition, a summary of possible measurements that can be carried out from the present arrangement is also highlighted. Experimental results using a four-frame phase shifting technique are illustrated

  • 13.
    Nordin, Daniel
    et al.
    Luleå tekniska universitet.
    Hyyppä, Kalevi
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Advantages of a new modulation scheme in an optical self mixing FMCW system2002In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 41, no 5, p. 1128-1133Article in journal (Refereed)
    Abstract [en]

    A new frequency-modulated continuous wave modulation scheme, which gives correct results even when the Doppler shift is larger than the frequency difference associated with the range, is presented and tested with a tunable laser diode and fiber-based system. By inserting a constant frequency region in the modulation scheme, both the magnitude and the sign of all beat frequencies can be determined. When they are known, the correct frequency difference as a result of the range can be calculated. This new scheme gives more freedom when choosing the modulation parameters of the laser, because increasing the modulation frequency, and/or the frequency sweep, to avoid ambiguities resulting from a large Doppler shift no longer becomes necessary. This is especially useful when using a somewhat cheaper laser diode source, since the maximum obtainable modulation frequency and frequency sweep can be somewhat limited. The suggested modulation scheme makes it possible to use some laser diodes in an application they otherwise would not be suited for.

  • 14.
    Nordin, Daniel
    et al.
    Luleå University of Technology.
    Hyyppä, Kalevi
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Using a discrete thermal model to obtain a linear frequency ramping in a frequency-modulated continuous-wave system2005In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 44, no 7, p. 74202-Article in journal (Refereed)
    Abstract [en]

    The lasing wavelength of a single-section distributed feedback (DFB) laser diode can be modulated by modulating the drive current. This makes it possible to utilize the DFB laser diode in a frequency-modulated continuous wave (FMCW) range and velocity measuring system. In FMCW, the frequency of the laser is ramped, and the frequency difference between the reflected wave and a local-oscillator wave is monitored. For maximum performance the frequency ramping should be linear. Due to thermal phenomena, a linear ramping of the current seldom results in a linear ramping of the optical frequency. We have derived a discrete thermal model, using resistors and capacitors, of our laser module. The thermal model was then used as a starting point to model the frequency behavior of the laser and to derive modulation currents that resulted in a linear frequency ramping at some different modulation frequencies.

  • 15.
    Olsson, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Selective imaging of sound sources in air using phase-calibrated multiwavelength digital holographic reconstructions2007In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 46, p. 75801-Article in journal (Refereed)
    Abstract [en]

    A method for selective imaging using multiwavelength digital holographic reconstructions and the phase response of a sound source is demonstrated. Several sound measurements, using laser vibrometry, and digital reconstructions are made for several frequencies of the sound field emitted from two ultrasound transducers with different phase characteristics. Adding the reconstructed complex amplitudes together and applying a filter derived from the standard deviation over the phases for the different reconstructions makes possible a selective imaging of primary sources. When the imaging method is calibrated for a certain phase response, only primary sources with that particular phase response are imaged. Other sources and unwanted speckles are efficiently suppressed. The depth resolution obtained is 3 wavelengths.

  • 16.
    Olsson, Erik
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Forsberg, Fredrik
    Three-dimensional selective imaging of sound sources2009In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 48, no 3Article in journal (Refereed)
    Abstract [en]

    A technique for 3-D selective imaging of sound sources is described analytically and demonstrated experimentally. One-dimensional recordings of the acoustic field is measured using laser vibrometry. By applying digital holographic and tomographic algorithms to the acquired 1-D data, the full 3-D complex amplitude is reconstructed. The use of multiple frequencies in the spectral content of the acoustic field gives a number of advantages: higher spatial resolution, less noise in the reconstructed image, less sensitivity to noise in the measurements, and the possibility to perform selective imaging. Theory for all three steps-the measurement of sound using light, numerical propagation of waves, and finally the tomographic reconstruction in the process are given. In the experiment, the positions of three ultrasound sources are accurately determined and two different types of transducers are distinguished from each other. This multiwavelength technique could show to be a useful addition to optoacoustic imaging.

  • 17. Olsson, Erik
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Zipser, Lothar
    HTW, Hochschule für Technik und Wirtschaft, Dresden.
    Locating primary sound sources in scattering media using multifrequency digital holographic reconstruction2006In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 45, no 1Article in journal (Refereed)
    Abstract [en]

    Multifrequency digital holographic reconstructions of primary sound sources embedded in scattering media are demonstrated. The sound field is measured with a scanning laser Doppler vibrometer (LDV) and broadening of the spectral content of the sound source is achieved by tuning the primary ultrasound (US) transducer around its resonance frequency. The results show that combining the complex amplitudes from the different frequency reconstructions results in a reduced susceptibility to multiple scattered sound and makes possible a quite thorough localization of the primary sound source. The depth resolution obtained is 11 US frequencies. This depth sensitivity is improved even further to only 2.8 wavelengths by applying a filter determined from the standard deviation over the phases

  • 18.
    Saldner, Henrik
    et al.
    Luleå tekniska universitet.
    Mohan, Nandigana K.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Comparative TV holography for vibration analysis1995In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 34, no 2, p. 486-492Article in journal (Refereed)
  • 19.
    Saldner, Henrik O.
    et al.
    Luleå tekniska universitet.
    Huntley, Jonathan M.
    Loughborough University, Department of Mechanical Engineering.
    Profilometry using temporal phase unwrapping and a spatial light modulator based fringe projector1997In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 36, no 2, p. 610-615Article in journal (Refereed)
    Abstract [en]

    fringe projector based on a low-cost spatial light modulator has been used to measure the shapes of discontinuous objects. By changing the fringe phase and the fringe pitch, a sequence of wrapped phase maps can be acquired at different sensitivities. This sequence can then be converted to a surface profile by the recently proposed method of temporal unwrapping rather than by a conventional spatial unwrapping approach. The main advantages are that the method is simple and robust, and that objects with surface discontinuities are profiled as easily and accurately as smooth ones. The absolute distance from the camera to an object is measured at each pixel independently of the other pixels in the image. In addition to accurate measurement of surface shape, one possible application may therefore be as a 3-D robot vision system. A simple calibration procedure is described which avoids the need for accurate positioning of the camera and projector and which takes account of instrumental artifacts. A measurement accuracy better than 1/1000 of the field of view has been achieved. A number of practical applications of the technique are illustrated.

  • 20.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Dynamic properties of multispectral speckles in digital holography and image correlation2013In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 52, no 10, article id 101908Article in journal (Refereed)
    Abstract [en]

    I discuss dynamic properties of multispectral speckle in the context of digital holographic interferometry and image correlation. I outline the correlation of speckles in free space, in an imaging system, and, in the case of interferometric detection, caused by reflection off an inclined diffuse surface. It is shown that interferometric phase gradients and speckle movements are closely related where in fact the phase gradients are the generator of speckle movements in a defocused plane. The theory is exemplified by three typical situations encountered in image-plane digital holographic interferometry.

  • 21.
    Sjödahl, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Oreb, B.F.
    CSIRO, Lindfield, NSW.
    Stitching interferometric measurement data for inspection of large optical components2002In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 41, no 2, p. 4003-408Article in journal (Refereed)
    Abstract [en]

    An algorithm for stitching together a set of individual phase measurements into a unified larger phase map is presented. The set of individual phase maps results from scanning a component over the interferometer aperture and acquiring a measurement at each position. The algorithm is based on an iterative approach, where singular value decomposition is used to solve the rigid body movement problem between the different phase maps. The algorithm has been tested in numerical experiments and has been successfully applied to real data

  • 22.
    Sjödahl, Mikael
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Yamaguchi, I.
    Strain and torque measurements on cylindrical objects using the laser speckle strain gauge1996In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 35, no 4, p. 1179-1186Article in journal (Refereed)
  • 23.
    Synnergren, Per
    Luleå tekniska universitet.
    Measurement of three-dimensional displacement fields and shape using electronic speckle photography1997In: Optical Engineering: The Journal of SPIE, ISSN 0091-3286, E-ISSN 1560-2303, Vol. 36, no 8, p. 2302-2310Article in journal (Refereed)
    Abstract [en]

    A binocular stereo vision system for measurements of 3D displacement fields on predominantly flat objects is proposed. The system is based on the translated lens method and electronic speckle photography. This noncontact optical measuring method is inherently simple and provides invariant magnification independent of position; it is also characterized by high accuracy and calibration simplicity. The system is capable of measuring in-plane deformations with a standard deviation of less than 1 percent of the pixel size for small deformations. However, the practical limitations of the optical setup result in out-of-plane errors that are a factor of 4-6 larger than the corresponding in-plane component.

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