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3D localization in digital holography from scattered light from micrometer-sized particles
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-0398-1919
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

When a particle is illuminated by a beam of light it will scatter and redistribute the light in all directions. How it scatters depends on the size, shape and refractive index of the particle. Additionally, it depends on the wavelength and polarization of the illuminating beam. The direction and distance to the observer relative the particle also needs to be considered.  A digital holographic imaging system is used to collect parts of the scattered light from micrometer-sized particles. By utilizing digital holography a three-dimensional reconstruction of the imaged scene is possible. Traditionally, particles are localized based on the intensity in the holographic reconstructions. In this licentiate thesis, the phase response of the scattered light is investigated and utilized. An alternative method for locating spherical particles is presented. The method locate particles based on a simple feature of a propagating wave, namely the fact that the wavefront curvature changes from converging to diverging at the axial location of the particle. The wavefront curvature is estimated using two different methods. The first method estimates the lateral phase-gradients using a finite-difference method. The second method uses a three-dimensional parametric model based on a Chebyshev polynomial expansion. The methods are demonstrated using both simulations and experimental measurements. The simulations are based on the Lorenz-Mie scattering theory for spherical particles and are combined with an imaging system model. Experiments are performed using an off-axis polarization sensitive digital holographic system with a coherent Nd:YAG laser. Measurements of stationary particles are made to validate and evaluate the proposed method. It is found that these methods estimate the true axial position and does not have the offset that is associated with intensity-based methods. Additionally, it is possible to exclude noise that shows up as false particles since noise does not have the same phase response as a real particle. The second method, that uses a parametric model, also improves the standard deviation in the positioning.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords [en]
Digital Holography, Polarization, Particle Scattering, Metrology
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-68374ISBN: 978-91-7790-114-3 (print)ISBN: 978-91-7790-115-0 (electronic)OAI: oai:DiVA.org:ltu-68374DiVA, id: diva2:1198138
Presentation
2018-06-14, E243, Luleå Tekniska Universitet, Luleå, 09:00 (Swedish)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2014-4906Available from: 2018-04-17 Created: 2018-04-16 Last updated: 2018-06-12Bibliographically approved
List of papers
1. Improved particle position accuracy from off-axis holograms using a Chebyshev model
Open this publication in new window or tab >>Improved particle position accuracy from off-axis holograms using a Chebyshev model
2018 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, no 1, p. A157-A163Article in journal (Refereed) Published
Abstract [en]

Side scattered light from micrometer-sized particles is recorded using an off-axis digital holographic setup. From holograms, a volume is reconstructed with information about both intensity and phase. Finding particle positions is non-trivial, since poor axial resolution elongates particles in the reconstruction. To overcome this problem, the reconstructed wavefront around a particle is used to find the axial position. The method is based on the change in the sign of the curvature around the true particle position plane. The wavefront curvature is directly linked to the phase response in the reconstruction. In this paper we propose a new method of estimating the curvature based on a parametric model. The model is based on Chebyshev polynomials and is fit to the phase anomaly and compared to a plane wave in the reconstructed volume. From the model coefficients, it is possible to find particle locations. Simulated results show increased performance in the presence of noise, compared to the use of finite difference methods. The standard deviation is decreased from 3–39 μm to 6–10 μm for varying noise levels. Experimental results show a corresponding improvement where the standard deviation is decreased from 18 μm to 13 μm.

Place, publisher, year, edition, pages
Optical Society of America, 2018
Keywords
Digital holography, Scattering, particles, Mie theory, Image processing
National Category
Atom and Molecular Physics and Optics Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-66958 (URN)10.1364/AO.57.00A157 (DOI)000418614400020 ()2-s2.0-85039793350 (Scopus ID)
Funder
Swedish Research Council, 621-2014-4906
Note

Validerad;2018;Nivå 2;2017-12-15 (andbra)

Available from: 2017-12-11 Created: 2017-12-11 Last updated: 2018-04-16Bibliographically approved
2. Off-axis digital holographic particle positioning based on polarization-sensitive wavefront curvature estimation
Open this publication in new window or tab >>Off-axis digital holographic particle positioning based on polarization-sensitive wavefront curvature estimation
2016 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 55, no 27, p. 7503-7510Article in journal (Refereed) Published
Abstract [en]

Poor axial resolution in holographic particle imaging applications makes particle positioning in 3D space morecomplex since the positions are not directly obtained. In this paper we estimate the axial position of micrometerparticles by finding the location where the wavefront curvature from the scattered light becomes zero. By record-ing scattered light at 90°using off-axis holography, the complex amplitude of the light is obtained. Byreconstruction of the imaged scene, a complex valued volume is produced. From this volume, phase gradientsare calculated for each particle and used to estimate the wavefront curvature. From simulations it is found that thewavefront curvature became zero at the true axial position of the particle. We applied this metric to track an axialtranslation experimentally using a telecentric off-axis holographic imaging system with a lateral magnification ofM1.33. A silicon cube with molded particles inside was used as sample. Holographic recordings are performedboth before and after a 100μm axial translation. From the estimated positions, it was found that the mean dis-placement of particles between recordings was 105.0μm with a standard deviation of 25.3μm.

Place, publisher, year, edition, pages
Optical Society of America, 2016
Keywords
Digital holography, Scattering, Particles
National Category
Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-59662 (URN)10.1364/AO.55.007503 (DOI)000383996900008 ()2-s2.0-84988878500 (Scopus ID)
Funder
Swedish Research Council, 621-2014-4906
Note

Validerad; 2016; Nivå 2; 2016-10-25 (andbra)

Available from: 2016-10-11 Created: 2016-10-11 Last updated: 2018-07-10Bibliographically approved
3. Axial Particle Positioning by Wavefront Parameterization using Chebyshev Polynomials and Off-axis Digital Holography
Open this publication in new window or tab >>Axial Particle Positioning by Wavefront Parameterization using Chebyshev Polynomials and Off-axis Digital Holography
2017 (English)In: Digital Holography and Three-Dimensional Imaging, Washington: The Optical Society , 2017, article id M4A.3Conference paper, Published paper (Refereed)
Abstract [en]

A particle can be axially positioned where its scattered light has a plane wavefront. The phase anomaly compared to a plane wave is fitted to 3D Chebyshev polynomial, where coefficients correspond to the axial position.

Place, publisher, year, edition, pages
Washington: The Optical Society, 2017
Series
Digital Holography and Three-Dimensional Imaging
Keywords
Particle Scattering, Digital Holography
National Category
Atom and Molecular Physics and Optics Applied Mechanics
Research subject
Experimental Mechanics
Identifiers
urn:nbn:se:ltu:diva-64069 (URN)10.1364/DH.2017.M4A.3 (DOI)2-s2.0-85026326255 (Scopus ID)978-1-943580-28-6 (ISBN)
Conference
Digital Holography and Three-Dimensional Imaging 2017, JeJu Island, South Korea, 29 May–1 June 2017
Funder
Swedish Research Council, 621-2014-4906
Available from: 2017-06-15 Created: 2017-06-15 Last updated: 2018-04-16Bibliographically approved

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