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  • 1.
    Hällstig, Emil
    et al.
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Svanbro, Angelica
    Characterization and compensation of decorrelations in interferometric set-ups using active optics2007In: Optical Measurement Systems for Industrial Inspection V / [ed] Wolfgang Osten; Christophe Gorecki; Erik L. Novak, Bellingham, Wash.: SPIE - International Society for Optical Engineering, 2007, p. 661619-Conference paper (Refereed)
    Abstract [en]

    Decorrelation in an interferometric set-up appears due to movements of the speckle pattern. In the case of rigid body movements the effect of decorrelation severely limits the performance of speckle interferometers. If the movement is larger than the speckle size the wanted phase information of the deformation is lost. Phase modulating spatial light modulators (SLMs) provide a new method to non-mechanically deflect and shape light. By using the SLM for scanning the field-of-view and focusing at different distances it is possible to measure intensity speckle patterns in a three-dimensional volume. These intensity images can then be cross correlated to give a three-dimensional correlation coefficient of the speckle pattern. If an SLM is utilized in an interferometric set-up it is possible to compensate for unwanted movements during an experiment. The measured correlation coefficient will then provide information regarding how large movements that are allowed with maintained performance of the interferometer. It is shown that for large movements the SLM can be used to retrieve phase maps.

  • 2.
    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

  • 3. Molin, Nils-Erik
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Gren, Per
    Svanbro, Angelica
    Speckle photography combined with speckle interferometry2004In: Optics and lasers in engineering, ISSN 0143-8166, E-ISSN 1873-0302, Vol. 41, no 4, p. 673-686Article in journal (Refereed)
    Abstract [en]

    By combining speckle interferometry (SI) measurements with speckle photography, the fringe visibility can be kept high despite the presence of a large bulk or rotating motion of the object. This combined technique improves the usability and measuring range of both pulsed and phase-stepped Sl-methods. This paper reviews the theory of fringe formation in Sl and shows some recent applications of this combined technique

  • 4. Molin, Nils-Erik
    et al.
    Svanbro, Angelica
    Gren, Per
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Sjödahl, Mikael
    Combined digital speckle photography (DSP) and interferometry2001In: Second international conference on experimental mechanics, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2001Conference paper (Refereed)
    Abstract [en]

    A general problem in optical metrology is to measure a deformation field when this field is added to a translation or a rotational motion. Methods like Speckle Photography (SP) do handle large rigid body motions but the results might be of too poor accuracy to resolve the deformation field. Interferometric methods on the other hand might measure the deformation field but the bulk motion makes the fringes disappear. By combining Digital Speckle Photography, Dsp, (also called digital correlation) with Speckle Interferometry, SI, (also called ESPI, DSPI, TV holography, pulsed TV holography) or with shearography (TV shearography) such measuring situations can be mastered.

  • 5.
    Svanbro, Angelica
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    DSPI: complex amplitude correlation for large in-plane compensations and phase evaluation2006In: Speckle06: speckles, from grains to flowers ; 13 - 15 September 2006, Nimes, France ; [proceedings] / [ed] Pierre Slangen; Christine Cerruti, Bellingham, Wash: SPIE - International Society for Optical Engineering, 2006, p. 63410I-Conference paper (Refereed)
    Abstract [en]

    The use of complex amplitude correlation to determine the deformation field for in-plane motions in digital speckle pattern interferometry (DSPI) is investigated. The result is compared to experiments where only DSPI-algorithms, as well as where combined DSPI - intensity correlation are used. Experiments with and without large rigid body motions are studied. An advantage of using complex amplitude correlation instead of intensity correlation is that the phase change describing the deformation is retrieved directly from the correlation peak and there is no need to compensate for the large movement and then use interferometric algorithms to obtain the phase information. A discovered drawback of this method is that the correlation values drops very quick if there is a phase gradient larger than K across the sub image used for the cross correlation. This means that in order to use the complex amplitude correlation the size of the subimages must be proportional to the magnitude of the present deformation gradient. Or, a third parameter in the crosscorrelation algorithm that compensates for the phase variation is needed.

  • 6. Svanbro, Angelica
    In-plane dynamic speckle interferometry: comparison between a combined speckle interferometry/speckle correlation and an update of the reference image2004In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 43, no 21, p. 4172-4177Article in journal (Refereed)
    Abstract [en]

    A common problem during study of, for instance, tensile tests with interferometers is that the sample moves too much so that the speckles decorrelate and no phase information is obtained. Two ways to overcome this problem are compared: a combination of speckle interferometry and speckle correlation and a method in which the reference image is updated during the experiment. The comparison shows that both techniques can be used to measure the deformation of an object even if it is exposed to rigid body motions. Both techniques are applied to measurements of microscale deformation fields of an adhesive joint in a carbon-fiber epoxy composite

  • 7. Svanbro, Angelica
    Speckle interferometry and correlation applied to large-displacement fields2004Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A common problem in experimental mechanics is that when a sample is studied in e.g. a tensile test machine, the sample is often exposed to rigid body motions at the same time as small deformations occur. These two movements, the rigid body motion and the deformation, are often talked about as displacement fields. The sought deformation field is often in the micrometer range while the rigid body motions often are of millimetre or centimetre size. Therefore, it is often a problem to resolve the deformation field since it is drowned by the larger movement of the object. The displacement field can be measured with methods like speckle correlation, but the results might be of too poor accuracy to resolve the deformation field. Interferometric methods on the other hand might measure the deformation field but the rigid body motion makes the fringes disappear. In this thesis two methods are presented that makes it possible to master such measuring situations: a combination of speckle interferometry/speckle correlation and a method where the reference image is updated frequently during the experiment. Both theory and experiments are presented. For the combined speckle interferometry/speckle correlation, it is shown that the information necessary to apply the speckle correlation method is already available in interferometric recordings. With only minor changes in the calculation procedures, the speckle motion in the recordings can be determined. Interference fringes, which have disappeared due to large speckle motions, are retrieved by digital compensation for this motion. The speckle correlation technique gives the motion of the whole surface of the object so different areas of the object can move different amounts and in different directions and it is still possible to retrieve the fringes describing the deformation field. Updating the reference image during the experiment is another method used. As soon as the specimen has moved 1/10 of a speckle the reference image is updated in order to avoid speckle decorrelation. In this way the total movement of the surface is added up during the experiment and a phase map describing the displacement of the object is achieved. Finally, the magnitude of the shear in shearography is measured using speckle correlation. This allows quantitative measurements of the spatial derivative of the deformation field in shearography.

  • 8. Svanbro, Angelica
    et al.
    Huntley, J.M.
    Loughborough University.
    Davila, A.
    Centro de Investigaciones en Optica, Loma del Bosque.
    Optimal re-referencing rate for in-plane dynamic speckle interferometry2003In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 42, no 2, p. 251-258Article in journal (Refereed)
    Abstract [en]

    We investigate experimentally the optimal rate at which the reference speckle pattern should be updated when dynamic speckle interferometry is used to measure transient in-plane displacement fields. Images are captured with a high-speed camera and phase shifting and phase unwrapping are done temporally. For a wide range of in-plane velocities, up to a maximum of 40% of the Nyquist limit, the random errors in the calculated displacement field are minimized by updating the reference speckle pattern after a speckle displacement of 1 /10 of the pixel spacing. The technique is applied to measurements of microscale deformation fields within an adhesive joint in a carbon-fiber epoxy composite.

  • 9. Svanbro, Angelica
    et al.
    Sjödahl, Mikael
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Complex amplitude correlation for compensation of large in-plane motion in digital speckle pattern interferometry2006In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 45, no 34, p. 8641-8647Article in journal (Refereed)
    Abstract [en]

    The use of complex amplitude correlation to compensate for large in-plane motion in digital speckle pattern interferometry is investigated. The result is compared with experiments where digital speckle photography (DSP) is used for compensation. An advantage of using complex amplitude correlation instead of intensity correlation (as in DSP) is that the phase change describing the deformation is retrieved directly from the correlation peak, and there is no need to compensate for the large movement and then use the interferometric algorithms. A discovered drawback of this method is that the correlation values drop quickly if a phase gradient larger than π is present in the subimages used for cross correlation. This means that, for the complex amplitude correlation to be used, the size of the subimages must be well chosen or a third parämeter in the cross-correlation algorithm that compensates for the phase variation is needed. Correlation values and wrapped phase maps from the two techniques (intensity and complex amplitude correlation) are presented.

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