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Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements

The main goal of this research was to assess if it is possible to evaluate the thickness of thin layers (both thin films on the surface and thin layers below the surface of the tested object) and foils using optical coherence tomography (OCT) for thickness assessment under the resolution of the stan...

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Autores principales: Kamińska, Aleksandra M., Strąkowski, Marcin R., Pluciński, Jerzy
Formato: Online Artículo Texto
Lenguaje:English
Publicado: MDPI 2020
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7582414/
https://www.ncbi.nlm.nih.gov/pubmed/33023212
http://dx.doi.org/10.3390/s20195653
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author Kamińska, Aleksandra M.
Strąkowski, Marcin R.
Pluciński, Jerzy
author_facet Kamińska, Aleksandra M.
Strąkowski, Marcin R.
Pluciński, Jerzy
author_sort Kamińska, Aleksandra M.
collection PubMed
description The main goal of this research was to assess if it is possible to evaluate the thickness of thin layers (both thin films on the surface and thin layers below the surface of the tested object) and foils using optical coherence tomography (OCT) for thickness assessment under the resolution of the standard commercially available OCT measurement system. In the proposed solution, light backscattered from the evaluated thin layer has been expressed as a multiple beam interference. Therefore, the OCT system was modeled as a two-beam interferometer (e.g., Michelson), in which one beam propagates from the reference arm and the other comes from a Fabry–Pérot interferometer. As a consequence, the mathematical model consists of the main Michelson interferometer, in which the measuring arm represents the Fabry–Pérot interferometer. The parameters of the layer (or foil) are evaluated by analyzing the minimum value of the interference contrast. The model developed predicts the behavior of the thin layers made from different materials (with different refractive indexes) with different thickness and located at different depths. To verify the correctness of the proposed model, an experiment with a wedge cell has been carried out. The wedge cell was shifted across the scanning beam using a linear translation stage with a micrometer screw under the scanning head. The relationship between the thickness of the gap of the wedge cell and the OCT output signal is presented. For the additional verification of the proposed model, the results of the measurements of the thickness of the thin foil were compared with the theoretical results of the simulations. The film thickness was evaluated based on the calculated positions of the minimum value of interference contrast. A combination of the standard potentialities of OCT with the proposed approach to analyzing the signal produces new metrological possibilities. The method developed allows us to evaluate thickness under the resolution of the system and the location of the layer as well. This produces the possibility of measuring a layer which is covered by another layer. Moreover, it is possible to create a thickness map with high sensitivity to thickness changes. These experiments and simulations are the culmination of preliminary research for evaluating the potential of the proposed measurement method.
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spelling pubmed-75824142020-10-29 Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements Kamińska, Aleksandra M. Strąkowski, Marcin R. Pluciński, Jerzy Sensors (Basel) Article The main goal of this research was to assess if it is possible to evaluate the thickness of thin layers (both thin films on the surface and thin layers below the surface of the tested object) and foils using optical coherence tomography (OCT) for thickness assessment under the resolution of the standard commercially available OCT measurement system. In the proposed solution, light backscattered from the evaluated thin layer has been expressed as a multiple beam interference. Therefore, the OCT system was modeled as a two-beam interferometer (e.g., Michelson), in which one beam propagates from the reference arm and the other comes from a Fabry–Pérot interferometer. As a consequence, the mathematical model consists of the main Michelson interferometer, in which the measuring arm represents the Fabry–Pérot interferometer. The parameters of the layer (or foil) are evaluated by analyzing the minimum value of the interference contrast. The model developed predicts the behavior of the thin layers made from different materials (with different refractive indexes) with different thickness and located at different depths. To verify the correctness of the proposed model, an experiment with a wedge cell has been carried out. The wedge cell was shifted across the scanning beam using a linear translation stage with a micrometer screw under the scanning head. The relationship between the thickness of the gap of the wedge cell and the OCT output signal is presented. For the additional verification of the proposed model, the results of the measurements of the thickness of the thin foil were compared with the theoretical results of the simulations. The film thickness was evaluated based on the calculated positions of the minimum value of interference contrast. A combination of the standard potentialities of OCT with the proposed approach to analyzing the signal produces new metrological possibilities. The method developed allows us to evaluate thickness under the resolution of the system and the location of the layer as well. This produces the possibility of measuring a layer which is covered by another layer. Moreover, it is possible to create a thickness map with high sensitivity to thickness changes. These experiments and simulations are the culmination of preliminary research for evaluating the potential of the proposed measurement method. MDPI 2020-10-02 /pmc/articles/PMC7582414/ /pubmed/33023212 http://dx.doi.org/10.3390/s20195653 Text en © 2020 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
spellingShingle Article
Kamińska, Aleksandra M.
Strąkowski, Marcin R.
Pluciński, Jerzy
Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements
title Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements
title_full Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements
title_fullStr Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements
title_full_unstemmed Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements
title_short Spectroscopic Optical Coherence Tomography for Thin Layer and Foil Measurements
title_sort spectroscopic optical coherence tomography for thin layer and foil measurements
topic Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7582414/
https://www.ncbi.nlm.nih.gov/pubmed/33023212
http://dx.doi.org/10.3390/s20195653
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