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Quantitative measurement of thin phase objects: comparison of speckle deflectometry and defocus-variant lateral shear interferometry
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-4879-8261
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0003-4853-870X
2018 (English)In: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 57, no 14, p. 3645-3652Article in journal (Refereed) Published
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.

Place, publisher, year, edition, pages
Optical Society of America, 2018. Vol. 57, no 14, p. 3645-3652
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics; Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-68878DOI: 10.1364/AO.57.003645ISI: 000431880000003Scopus ID: 2-s2.0-85046971352OAI: oai:DiVA.org:ltu-68878DiVA, id: diva2:1209740
Note

Validerad;2018;Nivå 2;2018-05-24 (andbra)

Available from: 2018-05-24 Created: 2018-05-24 Last updated: 2018-05-28Bibliographically approved

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Sjödahl, MikaelAmer, Eynas

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