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  • 1.
    Amer, Eynas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Edenharder, Stefan
    Institut für Technische Optik, Universität Stuttgart.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Stimulated Raman scattering holography for time-resolved imaging of methane gas2016Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, nr 13, s. 3429-3434Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, pulsed digital holographic detection is coupled to the stimulated Raman scattering (SRS) process for imaging gases. A Q-switched Nd-YAG laser (532 nm) has been used to pump methane gas (CH4) at pressures up to 12 bars. The frequency-tripled (355 nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) has been tuned to 629.93 nm so that the frequency difference between the pump (532 nm) and the Stokes beams fits a Raman active vibrational mode of the methane molecule (2922 cm(-1)). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped in time, space, and polarization on the gas molecules, resulting in a stimulated Raman gain of the Stokes beam and a corresponding loss of the pump beam through the SRS process. The resulting gain of the Stokes beam has been detected using pulsed digital holography by blending it with a reference beam on the detector. Two holograms of the Stokes beam, without and with the pump beam fringes present, were recorded. Intensity maps calculated from the recorded digital holograms showed amplification of the Stokes beam at the position of overlap with the pump beam fringes and the gas molecules. The gain of the Stokes beam has been separated from the background in the Fourier domain. A gain of about 4.5% at a pump beam average intensity of 4 MW/cm(2) and a Stokes beam intensity of 0.16 MW/cm(2) have been recorded at a gas pressure of 12 bars. The gain decreased linearly with decreasing gas pressure. The results show that SRS holography is a promising technique to pinpoint a specific species and record its spatial and temporal distribution

  • 2.
    Amer, Eynas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Single-shot polarization digital holography for recording stimulated Raman scattering signal for time-resolved measurement of gaseous species2017Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 56, nr 36, s. 10016-10023Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The stimulated Raman scattering (SRS) process is sensitive to the relation between the polarization direction of the two laser beams (the pump and the Stokes) that generate it. In this paper, we made use of the polarization sensitivity of the SRS process and used polarization-resolved pulsed digital holography to record the signal from one single-shot hologram. The pump beam polarization was kept vertical, while the Stokes beam polarization was 45 deg. The two polarization components of the Stokes beam were recorded in a single hologram by blending the Stokes beam with two reference beams with orthogonal polarization on the detector. The two components of the Stokes beam were separated in the Fourier domain, and the corresponding intensity maps were calculated. The vertically polarized component of the Stokes beam was amplified due to the SRS process, while the horizontal component experienced no gain. The difference between the vertically and horizontally polarized intensity maps, respectively, was calculated and Fourier transformed to separate the gain signal in the spatial frequency domain. The method was demonstrated on methane (CH4) gas at a pressure of 12 bars. Results show that SRS polarization holography is a promising technique for recording the SRS signal from one single-shot hologram for time-resolved monitoring of specific species. 

  • 3.
    Amer, Eynas
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Stimulated Raman scattering signals recorded by the use of an optical imaging technique2015Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, nr 20, s. 6377-6385Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, stimulated Raman scattering (SRS) signals have been recorded by an optical imaging technique that is based on spatial modulation. A frequency doubled Q-switched Nd:YAG laser (532 nm) was used to pump a polymethyl methacrylate (PMMA) target. The frequency tripled (355 nm) beam from the same laser was used to pump an optical parametric oscillator (OPO). The Stokes beam (from the OPO) was tuned to 631.27 nm so that the frequency difference between the pump and the Stokes beams fit the Raman active vibrational mode of the PMMA molecule (2956 cm(-1)). The pump beam has been spatially modulated with fringes produced in a Michelson interferometer. The pump and the Stokes beams were overlapped on the target resulting in a gain of the Stokes beam of roughly 2.5% and a corresponding loss of the pump beam through the SRS process. To demodulate the SRS signal, two images of the Stokes beam without and with the pump beam fringes present were recorded. The difference between these two images was calculated and Fourier transformed. Then, the gain of the Stokes beam was separated from the background in the Fourier domain. The results show that spatial modulation of the pump beam is a promising method to separate the weak SRS signal from the background.

  • 4. Andersson, Angelica
    et al.
    Mohan, N. Krishna
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    TV shearography: quantitative measurement of shear-magnitude fields by use of digital speckle photography2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 16, s. 2565-2568Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Digital speckle photography combined with TV shearography is developed for precise measurement of the magnitude of the shear field in a linear shear configuration. As an application the method is implemented to determine the slope-change variations of a three-dimensional object with TV shearography in which the shear magnitude is obtained with the digital speckle photography technique

  • 5.
    Andersson, Angelica
    et al.
    Luleå tekniska universitet.
    Runnemalm, Anna
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Digital speckle pattern interferometry: fringe retrieval for large in-plane deformations with digital speckle photography1999Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 38, nr 25, s. 5408-5412Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The compensation of large in-plane motions in digital speckle-pattern interferometry (DSPI) with the use of digital speckle photography (DSP) is demonstrated. Ordinary recordings of DSPI are recombined and analyzed with DSP. The DSP result is used to compensate for the bulk speckle motion prior to calculation of the phase map. This results in a high fringe contrast even for deformations of several speckle diameters. In addition, for the case of an in-plane deformation, it is shown that the absolute phase change in each pixel may be unwrapped by use of the DSP result as an initial guess. The principles of this method and experiments showing the in-plane rotation of a plate and the encounter of two rounded plates are presented

  • 6.
    Benckert, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    A method to resolve the 180° ambiguity in speckle photography1991Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 30, nr 4, s. 376-378Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    A new way of resolving the 180° ambiguity in speckle photography is presented. Results from a study of the deformation of a wooden block caused by drying illustrates the method

  • 7.
    Benckert, Lars
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Forsberg, Lars
    Molin, Nils-Erik
    Fresnel diffraction of a Gaussian laser beam by polished metal cylinders1990Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 29, nr 3, s. 416-421Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A laser beam touching the periphery of a polished cylinder is subjected to both diffraction and reflection. Inthe area where diffracted light and reflected light interact the resulting intensity distribution differs from thepattern predicted by diffraction theory for a sharp edge. The difference increases with cylinder radius. Inthis paper it is shown that a good description of the resulting intensity pattern is obtained by adding thereflected light amplitude to the diffracted amplitude as predicted by the Fresnel-Kirchhoff theory for a sharpedge.

  • 8.
    Bergström, David
    et al.
    Mid Sweden University.
    Powell, John
    Laser Expertise Ltd., Acorn Park Industrial Estate, Nottingham.
    Kaplan, Alexander
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Absorptance of nonferrous alloys to Nd:YLF and Nd:YAG laser light at room temperature2007Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, nr 8, s. 1290-1301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The measurement of absorptance is important for the analysis and modeling of laser-material interactions. Unfortunately, most of the absorptance data currently available consider only polished pure metals rather than the commercially available (unpolished, oxidized) alloys that are actually being processed in manufacturing. We present the results of absorptance measurements carried out at room temperature on as-received engineering grade nonferrous metals (Al, Cu, and Zn alloys). The measurements were made using an integrating sphere with a Nd:YLF laser at two wavelengths (1053 and 527 nm, which means that the results are also valid for Nd:YAG radiation at 1064 and 532 nm). The absorptance results obtained differ considerably from the existing data for polished, pure metals and should help improve the accuracy of laser-material interaction models. Some clear trends were identified. For all 22 cases studied the absorptance was higher than for ideal pure, polished metals. For all Al and Cu samples the absorptance was higher for the green than it was for the infrared wavelength, while for all Zn coatings this trend was reversed. No clear correlation between absorptance and surface roughness was found at low roughness values (Sa 0.15-0.60), but one rougher set of samples (Sa 2.34) indicated a roughness-absorptance correlation at higher roughness levels.

  • 9.
    Bergström, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Khodadad, Davood
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Dual-wavelength digital holography: single-shot shape evaluation using speckle displacements and regularization2014Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 53, nr 1, s. 123-131Artikel i tidskrift (Refereegranskat)
  • 10.
    Bhaduri, Basanta
    et al.
    National University of Singapore.
    Quan, Chenggen
    National University of Singapore.
    Tay, Cho Jui
    National University of Singapore.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Simultaneous measurement of translation and tilt using digital speckle photography2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 18, s. 3573-3579Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A Michelson-type digital speckle photographic system has been proposed in which one light beam produces a Fourier transform and another beam produces an image at a recording plane, without interfering between themselves. Because the optical Fourier transform is insensitive to translation and the imaging technique is insensitive to tilt, the proposed system is able to simultaneously and independently determine both surface tilt and translation by two separate recordings, one before and another after the surface motion, without the need to obtain solutions for simultaneous equations. Experimental results are presented to verify the theoretical analysis.

  • 11.
    Bruns, Marco
    et al.
    Universität Bremen, Institute of Environmental Physics.
    Buehler, Stefan
    Burrows, John P.
    Universität Bremen, Institute of Environmental Physics.
    Heue, Klaus-Peter
    University of Heidelberg, Institute of Environmental Physics.
    Platt, Ulrich
    University of Heidelberg, Institute of Environmental Physics.
    Pundt, Irene
    University of Heidelberg, Institute of Environmental Physics.
    Richter, Andreas
    Universität Bremen, Institute of Environmental Physics.
    Rozanov, Alexej
    Universität Bremen, Institute of Environmental Physics.
    Wagner, Thomas
    University of Heidelberg, Institute of Environmental Physics.
    Wang, Ping
    Universität Bremen, Institute of Environmental Physics.
    Retrieval of profile information from airborne multiaxis UV-visible skylight absorption measurements2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 22, s. 4415-4426Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A recent development in ground-based remote sensing of atmospheric constituents by UV-visible, absorption measurements of scattered light is the simultaneous use of several horizon viewing directions in addition to the traditional zenith-sky pointing. The different light paths through the atmosphere enable the vertical distribution of some atmospheric absorbers, such as NO2, BrO, or O-3, to be retrieved. This approach has recently been implemented on an airborne platform. This novel instrument, the airborne multiaxis differential optical absorption spectrometer (AMAXDOAS), has been flown for the first time. In this study, the amount of profile information that can be retrieved from such measurements is investigated for the trace gas NO2. Sensitivity studies on synthetic data are performed for a variety of representative measurement conditions including two wavelengths, one in the UV and one in the visible, two different surface spectral reflectances, various lines of sight (LOSs), and for two different flight altitudes. The results demonstrate that the AMAXDOAS measurements contain useful profile information, mainly at flight altitude and below the aircraft. Depending on wavelength and LOS used, the vertical resolution of the retrieved profiles is as good as 2 km near flight altitude. Above 14 km the profile information content of AMAXDOAS measurements is sparse. Airborne multiaxis measurements are thus a promising tool for atmospheric studies in the troposphere and the upper troposphere and lower stratosphere region.

  • 12.
    Casselgren, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Polarization resolved classification of winter road condition in the near-infrared region2012Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 51, nr 15, s. 3036-3045Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Three different configurations utilizing polarized short-wave infrared light to classify winter road conditions have been investigated. In the first configuration, polarized broadband light was detected in the specular and backward directions, and the quotient between the detected intensities was used as the classification parameter. Best results were obtained for the SS-configuration. This sensor was shown to be able to distinguish between the smooth road conditions of water and ice from the diffuse road conditions of snow and dry asphalt with a probability of wrong classification as low as 7%. The second sensor configuration was a pure backward architecture utilizing polarized light with two distinct wavelengths. This configuration was shown to be effective for the important problem of distinguishing water from ice with a probability of wrong classification of only 1.5%. The third configuration was a combination of the two previous ones. This combined sensor utilizing bispectral illumination and bidirectional detection resulted in a probability of wrong classification as low as 2% among all four surfaces.

  • 13.
    Casselgren, Johan
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Leblanc, James
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Angular spectral response from covered asphalt2007Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 46, nr 20, s. 4277-4288Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By measuring the spectral reflection from the four different road conditions dry, wet, icy, and snowy asphalt, a method of classification for the different surfaces -- using two and three wavelengths -- is developed. The method is tested against measurements to ascertain the probability of wrong classification between the surfaces. From the angular spectral response, the fact that asphalt and snow are diffuse reflectors and water and ice are reflective are confirmed.

  • 14.
    Echle, Georg
    et al.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Clarmann, Thomas von
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Dudhia, Anu
    Atmospheric, Oceanic, and Planetary Physics, Oxford University.
    Flaud, Jean-Marie
    Laboratoire de Photophysique Moléculaire, CNRS, Université Paris-Sud, Orsay.
    Funke, Bernd
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Glatthor, Norbert
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Kerridge, Brian
    Rutherford Appleton Laboratory, Oxfordshire.
    López-Puertas, Manuel
    Instituto de Astrofísica de Andalucía CSIC, Granada.
    Martin-Torres, Javier
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Stiller, Gabriele P.
    Forschungszentrum Karlsruhe, Institut für Meteorologie und Klimaforschung Karlsruhe.
    Optimized spectral microwindows for data analysis of the Michelson Interferometer for Passive Atmospheric Sounding on the Environmental Satellite2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 30, s. 5531-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    For data analysis of the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS) atmospheric limb emission spectroscopic experiment on Environmental Satellite microwindows, i.e., small spectral regions for data analysis, have been defined and optimized. A novel optimization scheme has been developed for this purpose that adjusts microwindow boundaries such that the total retrieval error with respect to measurement noise, parameter uncertainties, and systematic errors is minimized. Dedicated databases that contain optimized microwindows for retrieval of vertical profiles of pressure and temperature, H2O, O3, HNO3, CH4, N2O, and NO2 have been generated. Furthermore, a tool for optimal selection of subsets of predefined microwindows for specific retrieval situations has been provided. This tool can be used further for estimating total retrieval errors for a selected microwindow subset. It has been shown by use of this tool that an altitude-dependent definition of microwindows is superior to an altitude-independent definition. For computational efficiency a dedicated microwindow-related list of spectral lines has been defined that contains only those spectral lines that are of relevance for MIPAS limb sounding observations.

  • 15.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bending wave propagation in rotating objects measured by pulsed TV holography2002Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 41, nr 34, s. 7237-7240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transient bending waves in a rotating hard disk is measured by means of pulsed TV holography. The speckle motion in the detector plane caused by the rotation is compensated for in the interference phase evaluation. The technique is all electronic and needs no image derotator

  • 16.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Pulsed TV holography combined with digital speckle photography restores lost interference phase2001Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 40, nr 14, s. 2304-2309Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The measuring of situations with optical measuring methods is difficult when a deformation field must be determined while it is superposed to comparatively large rotating or translating object motion. Interferometric methods such as pulsed TV holography might be suitable to measure the small transient deformation, but the often-large bulk motion makes the phase information disappear. However, by a combination of digital speckle photography (DSP) (also called digital image correlation) with pulsed TV holography, such measuring problems can be mastered. A method to calculate the bulk in-plane motion by DSP from the usual pulsed TV holography recordings and then to use this information to restore the interference phase is proposed. This technique may be attractive in the study of transient vibrations overlaid on rotating or translating motions.

  • 17.
    Gren, Per
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Schedin, Staffan
    Luleå tekniska universitet.
    Xide, Li
    Department of Modern Mechanics and Engineering, University of Science and Technology of China.
    Tomographic reconstruction of transient acoustic fields recorded by pulsed TV holography1998Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 37, nr 5, s. 834-840Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pulsed TV holography together with CT reconstruction were used to measure the three-dimensional distribution of transient acoustic fields in air. Holograms from several directions were directly recorded onto a CCD detector. From the recorded holograms, phase maps were quantitatively evaluated

  • 18.
    Huntley, J.M.
    et al.
    Cavendish Laboratory, University of Cambridge.
    Benckert, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Speckle interferometry: noise reduction by correlation fringe averaging1992Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 31, nr 14, s. 2412-2414Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A method for noise reduction in double-exposure speckle interferometry is proposed, based on averaging independent spatially filtered correlation fringe patterns

  • 19.
    Huntley, J.M.
    et al.
    Cavendish Laboratory, University of Cambridge.
    Goldrein, H.T.
    Cavendish Laboratory, University of Cambridge.
    Benckert, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Parallel processing system for rapid analysis of speckle-photography and particle-image-velocimetry data1993Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 32, nr 17, s. 3152-3155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An automated system has been constructed to process double-exposure speckle-photography andparticle-image-velocimetry images. A 3 × 3 array of laser beams probes the photograph, forming ninefringe patterns in parallel; these are then analyzed sequentially by digital computer and the use of atwo-dimensional Fourier-transform method. Results are presented showing that the random errors inthe measured displacements from such a system approach the expected speckle-noise-limited performance,with a total analysis time per displacement vector of 160 ms.

  • 20.
    Huntley, J.M.
    et al.
    Cavendish Laboratory, University of Cambridge.
    Saldner, Henrik
    Luleå tekniska universitet.
    Temporal phase-unwrapping algorithm for automated interferogram analysis1993Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 32, nr 17, s. 3047-3052Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A new algorithm is proposed for unwrapping interferometric phase maps. Existing algorithms searchthe two-dimensional spatial domain for 2ir discontinuities: only one phase map is required, but phaseerrors can propagate outward from regions of high noise, corrupting the rest of the image. Analternative approach based on one-dimensional unwrapping along the time axis is proposed. It isapplicable to an important subclass of interferometry applications, in which a sequence of incrementalphase maps can be obtained leading up to the final phase-difference map of interest. A particularexample is quasi-static deformation analysis. The main advantages are (i) it is inherently simple, (ii)phase errors are constrained within the high-noise regions, and (iii) phase maps containing globaldiscontinuities are unwrapped correctly, provided the positions of the discontinuities remain fixed withtime. The possibility of real-time phase unwrapping is also discussed

  • 21. Johansson, Eva-Lena
    et al.
    Benckert, Lars
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Improving the quality of phase maps in phase object digital holographic interferometry by finding the right reconstruction distance2008Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, nr 1, s. 1-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Improved quality of phase maps in pulsed digital holographic interferometry is demonstrated by finding the right reconstruction distance. The objective is to improve the optical phase information when the object under study is a phase object and when it is out of focus, leading to low contrast fringes in the phase map. A numerical refocusing is performed by introducing an ideal lens as a multiplication by a phase field in the Fourier domain, and then a region of maximum speckle correlation is found by comparing undisturbed and disturbed sub-images in different refocused imaging planes. After finding the right reconstruction distance, a phase map of high visibility is constructed. By this technique a 30 % reduction of the phase error for a flow of Helium gas and a 50 % reduction of the phase error for a weak thin lens were obtained, which resulted in a significant improvement of the visual appearance of the phase maps.

  • 22. Johansson, Eva-Lena
    et al.
    Benckert, Lars
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase object data obtained by pulsed TV holography and defocused laser speckle displacement2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 16, s. 3235-3240Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transient events in optically transparent media occur in many engineering applications. Using pulsed TV holography to capture a laser speckle field propagated through an optical disturbance makes it possible to obtain both the position and the phase gradients of the disturbance. The technique depends on the fact that speckles transmitted through an optical disturbance will be displaced by an amount that depends on the relation of the defocus to the object. First the speckle field is captured holographically, without and with disturbance present. Then the recorded fields are numerically refocused in a computer to a number of different focal planes. With a cross-correlation technique a number of speckle displacement fields are obtained, and from them the data about the disturbance are obtained. So far the technique has been shown to work for thin objects

  • 23. Johansson, Eva-Lena
    et al.
    Benckert, Lars
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase object data obtained from defocused laser speckle displacement2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 16, s. 3229-34Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    An optical technique that is based on defocused digital speckle photography is proposed for the evaluation of phase objects. Phase objects are different kinds of transparent or semi-transparent media that allow light to be transmitted. A phase object inserted in a laser speckle field introduces speckle displacement, from which information about the object may be extracted. It is shown that one may use speckle displacements to determine both the phase gradients and the positions of phase objects. As an illustration the positions and focal lengths of two weak lenses have been derived from defocused laser speckle displacement

  • 24.
    Khodadad, Davood
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase-derivative-based estimation of digital reference wave from single off-axis digital hologram2016Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, nr 7, s. 1663-1669Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper describes a method to obtain an estimated digital reference wave from a single off-axis digital hologram that matches the actual experimental reference wave as closely as possible. The proposed method is independent of a reference flat plate and speckles. The digital reference wave parameters are estimated directly from the recorded phase information. The parameters include both the off-axis tilt angle and the curvature of the reference wave. Phase derivatives are used to extract the digital reference wave parameters without the need for a phase unwrapping process. Thus, problems associated with phase wrapping are avoided. Experimental results for the proposed method are provided. The simulated effect of the digital reference wave parameters on the reconstructed image phase distribution is shown. The pseudo phase gradient originating from incorrect estimation of the digital reference wave parameters and its effect on object reconstruction are discussed.

  • 25.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Bergström, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Matematiska vetenskaper.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Fast and robust automatic calibration for single-shot dual-wavelength digital holography based on speckle displacements2015Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 54, nr 16, s. 5003-5010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to describe a fast and robust automatic single-shot dual-wavelength holographic calibration method that can be used for online shape measurement applications. We present a model of the correction in two terms for each lobe, one to compensate the systematic errors caused by off-axis angles and the other for the curvature of the reference waves, respectively. Each hologram is calibrated independently without a need for an iterative procedure or information of the experimental set-up. The calibration parameters are extracted directly from speckle displacements between different reconstruction planes. The parameters can be defined as any fraction of a pixel to avoid the effect of quantization. Using the speckle displacements, problems associated with phase wrapping is avoided. The procedure is shown to give a shape accuracy of 34 μm using a synthetic wavelength of 1.1 mm for a measurement on a cylindrical test object with a trace over a field of view of 18  mm×18  mm.

  • 26.
    Khodadad, Davood
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Singh, Alok Kumar
    Institute of Applied Optics, University of Stuttgart.
    Pedrini, Giancarlo
    Institute of Applied Optics, University of Stuttgart.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Full-field 3D deformation measurement: Comparison between speckle phase and displacement evaluation2016Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, nr 27, s. 7735-7743Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The objective of this paper is to describe a full-field deformation measurement method based on 3D speckle displacements. The deformation is evaluated from the slope of the speckle displacement function that connects the different reconstruction planes. For our experiment, a symmetrical arrangement with four illuminations parallel to the planes (x,z) and (y,z) was used. Four sets of speckle patterns were sequentially recorded by illuminating an object from the four directions, respectively. A single camera is used to record the holograms before and after deformations. Digital speckle photography is then used to calculate relative speckle displacements in each direction between two numerically propagated planes. The 3D speckle displacements vector is calculated as a combination of the speckle displacements from the holograms recorded in each illumination direction. Using the speckle displacements, problems associated with rigid body movements and phase wrapping are avoided. In our experiment, the procedure is shown to give the theoretical accuracy of 0.17 pixels yielding the accuracy of 2 × 10-3 in the measurement of deformation gradients

  • 27.
    Kinell, Lars
    Luleå tekniska universitet.
    Spatiotemporal approach for real-time absolute shape measurements by use of projected fringes2004Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, nr 15, s. 3018-3027Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A spatiotemporal approach for fast absolute shape measurements is formulated. In principle, the Takeda method is used in combination with the reduced temporal phase-unwrapping scheme to calculate the absolute phase. Three different measurements are performed: a flat surface, steps, and a curved beam with varying cross sections. The performance in standard deviation is improved, and the success rate is approximately the same as that obtained with a strict temporal solution for which a four-bucket phase algorithm is used. The multichannel approach is also used. Then only one static image is needed. It should therefore be possible to measure objects in motion

  • 28.
    Kinell, Lars
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Robustness of reduced temporal phase unwrapping in the measurement of shape2001Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 40, nr 14, s. 2297-2303Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The predictions of success rate and depth uncertainty for the negative exponential sequence used for temporal phase unwrapping of shape data are generalized to include the effect of a reduced sequence and speckle noise in single-channel and multichannel systems, respectively. To cope with the reduction of the sequence, a scaling factor is introduced. A thorough investigation is made of the performance of this algorithm, called the reduced temporal phase-unwrapping algorithm. Two different approaches are considered: a single-channel approach in which all the necessary images are acquired sequentially in time and a multichannel approach in which the three channels of a color CCD camera are used to carry the phase-stepped images for each fringe density in parallel. The performance of these two approaches are investigated by numerical simulations. The simulations are based on a physical model in which the speckle contrast, the fringe modulation, and random noise are considered the sources of phase errors. Expressions are found that relate the physical quantities to phase errors for the single-channel and the multichannel approaches. In these simulations the single-channel approach was found to be the most robust. Expressions that relate the measurement accuracy and the unwrapping reliability, respectively, with the reduction of the fringe sequence were also found. As expected, the measurement accuracy is not affected by a shorter fringe sequence, whereas a significant reduction in the unwrapping reliability is found as compared with the complete negative exponential sequence

  • 29.
    Lycksam, Henrik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Gren, Per
    Measurement of spatiotemporal phase statistics in turbulent air flow using high-speed digital holographic interferometry2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 8, s. 1314-1322Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We describe a method of measuring spatiotemporal (ST) structure and covariance functions of the phase fluctuations in a collimated light beam propagated through a region of refractive index turbulence. The measurements are performed in a small wind tunnel, in which a turbulent temperature field is created using heated wires at the inlet of the test section. A collimated sheet of light is sent through the channel, and the phase fluctuations across the sheet are measured. The spatial phase structure function can be estimated from a series of images captured at an arbitrary frame rate by spatial phase unwrapping, whereas the ST structure function requires a time resolved measurement and a full three-dimensional unwrapping. The measured spatial phase structure function shows agreement with the Kolmogorov theory with a pronounced inertial subrange, which is taken as a validation of the method. Because of turbulent mixing in the boundary layers close to the walls of the channel, the flow will not obey the Taylor hypothesis of frozen turbulence. This can be clearly seen in the ST structure function calculated in a coordinate system that moves along with the bulk flow. At zero spatial separation, this function should always be zero according to the Taylor hypothesis, but due to the mixing effect there will be a growth in the structure function with increasing time difference depending on the rate of mixing.

  • 30. Lycksam, Henrik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Leblanc, James
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wiener filtering of interferometry measurements through turbulent air using an exponential forgetting factor2008Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, nr 16, s. 2971-2978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of imaging through turbulent media has been studied frequently in connection with astronomical imaging and airborne radars. Therefore most image restoration methods encountered in the literature assume a stationary object, e.g., a star or a piece of land. In this paper the problem of interferometric measurements of slowly moving or deforming objects in the presence of air disturbances and vibrations is discussed. Measurement noise is reduced by postprocessing the data with a digital noise suppression filter that uses a reference noise signal measured on a small stationary plate inserted in the field of view. The method has proven successful in reducing noise in the vicinity of the reference point where the size of the usable area depends on the degree of spatial correlation in the noise, which in turn depends on the spatial scales present in the air turbulence. Vibrations among the optical components in the setup tend to produce noise that is highly correlated across the field of view and is thus efficiently reduced by the filter. © 2008 Optical Society of America.

  • 31.
    Miroshnikova, Natalia
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sarady, Istvan
    Percussion hole drilling of metals with a fourth-harmonic Nd:YAG laser studied by defocused laser speckle correlation2005Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 44, nr 17, s. 3403-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Defocused speckle correlation is introduced as a tool for measuring the response in metal sheets during percussion laser drilling. For this procedure the fourth-harmonic Nd:YAG wavelength (266 nm) was used in pulsed mode. The method provides a cost-efficient and robust alternative to speckle interferometry for the study of the small deformations that appear during laser processing. The accuracy was shown to be of the order of a few tens of microradians for the tilt component that is measured, which translates to a few nanometers in deflection when the component is spatially integrated. In the measurements, deflections in the form of craters as large as 50 nm were detected on the back sides of silver and copper sheets. The diameters of the craters were 300 μm in the silver and 150 μm in the copper sheet; the output diameter of the hole was ~5 μm

  • 32.
    Mohan, N. Krishna
    et al.
    Indian Institute of Technology.
    Andersson, Angelica
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Molin, Nils-Erik
    Optical configuration for TV holography measurement of in-plane and out-of-plane deformations2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 4, s. 573-577Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A novel TV holography method is proposed for parallel evaluation of in-plane and out-of-plane deformation fields. The method permits a trade-off between in-plane and out-of-plane measuring sensitivity. A four-exposure, four-frame phase shifting technique is used in the experiments; the experimental results for an aluminum specimen subjected to both rotation in its own plane and a bending couple load at the center are presented

  • 33.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Photoacoustic holographic imaging of absorbers embedded in silicone2011Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 50, nr 17, s. 2551-2558Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Light absorbing objects embedded in silicone have been imaged using photoacoustic digital holography. The photoacoustic waves were generated using a pulsed Nd:YAG laser, λ=1064 nm, and pulse length=12 ns. When the waves reached the silicone surface, they were measured optically along a line using a scanning laser vibrometer. The acoustic waves were then digitally reconstructed using a holographic algorithm. The laser vibrometer is proven to be sensitive enough to measure the surface velocity due to photoacoustic waves generated from laser pulses with a fluence allowed for human tissue. It is also shown that combining digital holographic reconstructions for different acoustic wavelengths provides images with suppressed noise and improved depth resolution. The objects are imaged at a depth of 16.5 mm with a depth resolution of 0.5 mm.

  • 34.
    Olsson, Erik
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sjödahl, Mikael
    Photoacoustic waves generated in blood studied using pulsed digital holography2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 16, s. 3053-3058Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We studied photoacoustic waves using pulsed digital holography. The acoustic waves were generated in a reindeer blood target by absorption of an IR laser pulse, λ=1064 nm and pulse length=12 ns. The acoustic pressure waves were then imaged in water using a second collimated laser pulse at λ=532 nm2 μs after the first IR pulse. Quantitative information on acoustic wave properties such as three-dimensional shape and pressure distribution was calculated by applying the inverse Radon transform on the recorded projection. The pressure pulse had a flat and sharp front parallel with the blood surface, which indicates that the pressure was generated at the blood surface. The generated pressure was proportional to the laser fluence with the proportionality constant equal to 1.8±0.3 cm-1. According to existing data, the proportionality constant should be 1.4 cm-1 for oxygenated human blood, which made our calculations probable

  • 35.
    Paulsson, Lars
    et al.
    Luleå tekniska universitet.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Kato, Jun-ichi
    Optical Engineering Laboratory, The Institute of Physical and Chemical Research, RIKEN!, Wako.
    Yamaguchi, Ichirou
    Optical Engineering Laboratory, The Institute of Physical and Chemical Research, RIKEN!, Wako.
    Temporal phase unwrapping applied to wavelength-scanning interferometry2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 19, s. 3285-8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We demonstrate the use of temporal phase unwrapping in combination with wavelength-scanning interferometry. Two unwrapping strategies are considered: fitting to a reversed exponential sequence and complex Fourier-transform ranging. Measurement of a 10-μm step by use of an external-cavity laser diode is discussed

  • 36.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Casselgren, Johan
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Simplified model for light scattering from granular materials with varying moisture content2013Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 52, nr 17, s. 4006-4012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Reflection measurements were performed on dry and moistened sand grains and glass spheres, respectively. A simple model for determining the water content is proposed from looking at the reflection distribution in the plane of incidence. The model is a combination of two sheared cosine-functions and consists of only two parameters. One parameter controls whether the reflection is mainly in the forward or backward direction. The former is true when the water content is high and the latter is true when the material is dry. The other parameter gives an idea of the homogeneity of the material.

  • 37.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase errors due to speckles in laser fringe projection2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 11, s. 2047-2053Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When measuring a three-dimensional shape with triangulation and projected interference fringes it is of interest to reduce speckle contrast without destroying the coherence of the projected light. A moving aperture is used to suppress the speckles and thereby reduce the phase error in the fringe image. It is shown that the phase error depends linearly on the ratio between the speckle contrast and the modulation of the fringes. In this investigation the spatial carrier method was used to extract the phase, where the phase error also depends on filtering the Fourier spectrum. An analytical expression for the phase error is derived. Both the speckle reduction and the theoretical expressions for the phase error are verified by simulations and experiments. It was concluded that a movement of the aperture by three aperture diameters during exposure of the image reduces the speckle contrast and hence the phase error by 60%. In the experiments, a phase error of 0.2 rad was obtained.

  • 38.
    Rosendahl, Sara
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Hällstig, Emil
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Sjödahl, Mikael
    Shape measurement with one fringe pattern recording including a digital master2010Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 49, nr 14, s. 2622-2629Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a method in which the 3D shape of an object can be measured and compared to the shape of the digital master of the object, e.g., the computer-aided design model. The measurement is done using a stereo camera system and a single projected fringe pattern. Because the digital master is available, i.e., the expected shape is known, only one projection and image recording is necessary; thus, the method becomes fast. The idea in this work is to find homologous points in the cameras, i.e., points corresponding to the same object point, using the object information. An algorithm to find the homologous points is presented and a method to calculate shape is described. Given the ambiguity due to the fact that the phase in the images is wrapped, there is a maximum deviation from the master that can be correctly detected. An analytical expression for this deviation is derived. Results from the shape measurement of an object both with and without deviations from the digital master are also presented. In these measurements, where the measurement volume is approximately 1 dm3 and the fringe period on the object plane is about 1 mm, the accuracy is ≈± 40 μm, and a deviation of max ≈± 1.6mm can be correctly detected.

  • 39.
    Saldner, Henrik O.
    Luleå tekniska universitet.
    Phase-stepped television holographic technique for measuring phase and amplitude maps of small vibrations1996Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 35, nr 20, s. 3791-3798Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Phase stepping between frames in TV holography is combined with sinusoidal phase modulation to determine phase and amplitude distributions of objects vibrating with small amplitudes 1,l@20, where l is the wavelength of the laser light used2. This technique has applications in, for example, optical modal analysis and the determination of harmonic sound fields in air and water. The noise reductionthat is obtained with the phase-stepping technique reduces the number of interferograms needed by one-half, which can shorten experimental time. The technique is robust, easy to use, and illustrated bymodes of vibration in a simple plate and in a more complicated structure 1a violin2.

  • 40.
    Saldner, Henrik O.
    et al.
    Luleå tekniska universitet.
    Huntley, Jonathan M.
    Temporal phase unwrapping: application to surface profiling of discontinuous objects1997Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 36, nr 13, s. 2770-2775Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The recently proposed technique of temporal phase unwrapping has been used to analyze the phase maps from a projected-fringe phase-shifting surface profilometer. A sequence of maps is acquired while the fringe pitch is changed; the phase at each pixel is then unwrapped over time independently of the other pixels in the image to provide an absolute measure of surface height. The main advantage is that objects containing height discontinuities are profiled as easily as smooth ones. This contrasts with the conventional spatial phase-unwrapping approach for which the phase jump across a height discontinuity is indeterminate to an integral multiple of 2 . The error in height is shown to decrease inversely with the number of phase maps used.

  • 41.
    Saldner, Henrik O.
    et al.
    Luleå tekniska universitet.
    Molin, Nils-Erik
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Stetson, Karl A.
    Fourier-transform evaluation of phase data in spatially phase-biased TV holograms1996Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 35, nr 2, s. 332-336Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    TV holograms for spatial phase stepping are formed with a small angular offset between the object and the reference beams to give a spatial frequency bias to the pattern recorded by the TV camera. It is common to set the bias so that there is a 90° or 120° phase shift between adjacent pixels and to use the irradiance of three or more adjacent pixels to evaluate the phase of the interference. We report the Fourier-transform evaluation of such recordings to obtain their phase data. We also demonstrate the direct calculation of the phase difference between successive recordings without intermediate calculation of the random phase of each hologram. This technique is proposed as an approach to pulsed TV holography

  • 42.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Gren, Per
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Phase evaluation and speckle averaging in pulsed television holography1997Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 36, nr 17, s. 3941-3947Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Double-pulsed (image-plane) TV holograms of transient bending waves in plates are recorded on separate frames in a CCD camera. A small angular offset between the reference and object beams, giving a spatial-frequency bias to the recorded pattern, permits quantitative evaluation of the phase of the interference. The Fourier spectrum of the image exhibits distinct parts that can be filtered out and inverse transformed to yield the phase information. Three different apertures of the imaging system are tested: a single slit, a double slit, and a three-hole aperture. Spatial speckle averaging is possible in the cases of the double-slit and three-hole apertures

  • 43.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Pedrini, G.
    Institut für Technische Optik, Universität Stuttgart.
    Tiziani, H.J.
    Institut für Technische Optik, Universität Stuttgart.
    Santoyo, F.M.
    Centro de Investigaciones en Optica, Loma del Bosque.
    Simultaneous three-dimensional dynamic deformation measurements with pulsed digital holography1999Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 38, nr 34, s. 7056-7062Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The three deformation components x , y , z of a vibrating object are measured simultaneously by use of digital holography with a double-pulse ruby laser source. The object is illuminated from three different directions, each optically path matched with three reference beams such that three independent digital holograms are formed and added incoherently in one single CCD image. The optical phase difference between the two recordings taken for each hologram is quantitatively evaluated by the Fourier-transform method so that a set of three phase maps is obtained, representing the deformation along three sensitivity vectors. The total object deformation is obtained as a vector resultant from the data of the three phase maps. To give the full three-dimensional (3-D) description, the shape of the object is measured by the two-wavelength contouring method. Experiments are performed with a cylinder as the test object, transiently and harmonically excited. The 3-D deformation and shape measurement results are presented graphically.

  • 44.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Pedrini, Giancarlo
    Institut für Technische Optik, Universität Stuttgart.
    Tiziani, Hans J.
    Institut für Technische Optik, Universität Stuttgart.
    Pulsed digital holography for deformation measurements on biological tissues2000Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 39, nr 16, s. 2853-2857Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Digital holograms are recorded of biological tissues by use of a Q -switched double-pulsed ruby laser. An image-plane digital holography setup is used with a CCD camera for capturing two holograms with a short time separation (20 800 s). Subtraction of the phase distribution in two digital holograms yield a fringe phase map that shows the change in deformation of the tissue surface between the recordings. Experiments are performed on tissue from a pig that was excited by a short-shock pulse and on a human hand that was excited by sinusoidal stimulation. Results when the object is imaged through an endoscope are also presented. The technique could be an approach for measuring parameters like elasticity on biological tissues

  • 45.
    Schedin, Staffan
    et al.
    Luleå tekniska universitet.
    Pedrini, Giancarlo
    Tiziani, Hans J.
    Aggarwal, Anil K.
    Comparative study of various endoscopes for pulsed digital holographic interferometry2001Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 40, nr 16, s. 2692-2697Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A comparison of several endoscopes as object image carriers in pulsed digital holography is presented. Three multicore flexible fiber endoscopes of different spatial resolution and one rigid endoscope are investigated. The four endoscopes are integrated in a setup for the recording of digital holograms on a CCD camera. A double-pulsed ruby laser is used as the light source. A spatial carrier is introduced by an off-axis reference beam, which permits quantitative evaluation of the phase difference between two holograms recorded with a short time separation (5 -600 s). From reported studies it may be inferred that the quality of the phase maps so derived from digital holographic interferometry has a strong correlation to the spatial resolution of the multicore fiber used in these endoscopes. With the endoscopic technique combined with pulsed digital holography a number of useful applications (in areas such as medical endoscopy, micromechanics, and microelectronics) are envisaged for which access to the objects of interest is otherwise difficult.

  • 46.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Accuracy in electronic speckle photography1997Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 36, nr 13, s. 2875-2885Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electronic speckle photography is an accurate, easy-to-use, video-based technique for the analysis of two- and three-dimensional deformation fields and in-plane strain fields, based on numerical cross correlation. Through the use of statistical optics, simulated speckle patterns, and experiments the accuracy in electronic speckle photography was found to depend on correlation, speckle size, window size, and correlation filter. The estimated correlation was found to be the combined effect of three mutually competing factors because of classical speckle correlation, subimage overlap, and displacement gradients. In many applications white-light speckle patterns provide a more accurate estimate of the displacement field than do laser speckle patterns

  • 47.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Calculation of speckle displacement, decorrelation, and object-point location in imaging systems1995Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 34, nr 34, s. 7998-8010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    My purpose here is to outline a method for calculating the fundamental behavior of speckle patterns in imaging systems. The theory of speckle displacement and decorrelation to include imaging at a general oblique angle is extended to more imaging systems, and explicit formulas are given for the image-point-object-point relationship that is important when defocused speckle is used. The intermediate results can be reused for optical systems other than those presented here. The image-speckle displacement analyzed in the three systems is expressed equivalently. The speckle decorrelation is in general larger in a single-lens system than in a two-lens system and can be minimized by proper design of the system

  • 48.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Electronic speckle photography: increased accuracy by nonintegral pixel shifting1994Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 33, nr 28, s. 6667-6673Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Electronic speckle photography offers a simple and fast technique for measuring in-plane displacement fields in solid and fluid mechanics. An improved algorithm is presented and analyzed by use of both computer-simulated speckle patterns and real experiments. The idea of the improved algorithm is to maximize the correlation between correlated subimages from different images by shifting some of them by nonintegral pixel values. The improved algorithm was found to determine displacement components with an uncertainty of less than 1% of a pixel and with negligible systematic errors in ideal experimental conditions

  • 49.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Electronic speckle photography: measurement of in-plane strain fields through the use of defocused laser speckle1995Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 34, nr 25, s. 5799-5808Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High-accuracy, noncontact measurements of in-plane strain fields have been performed through the use of an electronic-speckle-photography system. The strain fields are extracted from the displacement of defocused laser speckle in a telecentric imaging system. Two different illumination configurations have been suggested, both of which use four illumination directions. Both configurations produce results of an accuracy according to Me/ΔL, where M is the demagnification of the telecentric imaging system, e is the random error in the speckle-displacement fields, and ΔL is the magnitude of the defocusing distance. The maximum defocusing distance possible was found to be restricted by the spatial resolution, especially at high magnifications. In experiments on a semicircularly and a rectangularly notched aluminum sheet, the principal strain field around the notch was measured with a random error in the strain field of less than 10 μstrain (μm/m)

  • 50.
    Sjödahl, Mikael
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Amer, Eynas
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Quantitative measurement of thin phase objects: comparison of speckle deflectometry and defocus-variant lateral shear interferometry2018Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, nr 14, s. 3645-3652Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The two techniques of lateral shear interferometry and speckle deflectometry are analyzed in a common optical system for their ability to measure phase gradient fields of a thin phase object. The optical system is designed to introduce a shear in the frequency domain of a telecentric imaging system that gives a sensitivity of both techniques in proportion to the defocus introduced. In this implementation, both techniques successfully measure the horizontal component of the phase gradient field. The response of both techniques scales linearly with the defocus distance, and the precision is comparative, with a random error in the order of a few rad/mm. It is further concluded that the precision of the two techniques relates to the transverse speckle size in opposite ways. While a large spatial coherence width, and correspondingly a large lateral speckle size, makes lateral shear interferometry less susceptible to defocus, a large lateral speckle size is detrimental for speckle correlation. The susceptibility for the magnitude of the defocus is larger for the lateral shear interferometry technique as compared to the speckle deflectometry technique. The two techniques provide the same type of information; however, there are a few fundamental differences. Lateral shear interferometry relies on a special hardware configuration in which the shear angle is intrinsically integrated into the system. The design of a system sensitive to both in-plane phase gradient components requires a more complex configuration and is not considered in this paper. Speckle deflectometry, on the other hand, requires no special hardware, and both components of the phase gradient field are given directly from the measured speckle deformation field.

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