Two-wavelengths laser-speckle technique for thickness determination of transparent layers on rough surfaces
In this work, a non-contacting laser-speckle technique and two different implementations thereof for measuring the thickness of thin transparent liquid layers on optically rough surfaces are presented. The optical system allows large stand-off distances and can be used in harsh environments and indu...
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Published in: | Measurement science & technology 2013-11, Vol.24 (11), p.115204-1-6, Article 115204 |
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Main Authors: | , |
Format: | Article |
Language: | eng |
Subjects: | |
Online Access: | Get full text |
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Summary: | In this work, a non-contacting laser-speckle technique and two different implementations thereof for measuring the thickness of thin transparent liquid layers on optically rough surfaces are presented. The optical system allows large stand-off distances and can be used in harsh environments and industrial applications. The thickness of the (oil) coating can be measured down into the μm range, which is below that of the surface roughness. The distribution of the coating depends on adhesive and cohesive forces, the temperature and primarily on the surface topography itself. The thickness of transparent coatings can be evaluated statistically considering wavelengths and roughness. We describe the two measurement principles and the data processing, present measurement results and discuss the advantages and disadvantages of both methods. For a better understanding, the theoretical considerations of the diffraction of sinusoidal phase gratings in the Fraunhofer region will be given. |
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ISSN: | 0957-0233 1361-6501 |