Measuring the absorption coefficient of optical materials with arbitrary shape or distribution within an integrating sphere



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Martínez Antón, Juan Carlos and Gómez Manzanares, Ángela and Álvarez Fernández-Balbuena, Antonio and Vázquez Moliní, Daniel (2021) Measuring the absorption coefficient of optical materials with arbitrary shape or distribution within an integrating sphere. Optics Express, 29 (17). pp. 26287-26303. ISSN 1094-4087

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The absorption coefficient of a material is classically determined by measuring the transmittance of a homogeneous sample contained within flat optical faces and under collimated illumination. For arbitrary shapes this method is impracticable. The characterization of inhomogeneous or randomly distributed samples such as granules, powders or fibers suffers the same problem. Alternatively, an integrating cavity permits us to illuminate a sample under a homogenous and isotropic light field where the analysis simplifies. We revisit this strategy and present a new formal basis based on simple radiometric laws and principles. We introduce a new concept to describe the absorption: the optical form factor. We tackle a rigorous treatment of several regular forms, including full absorption range and the reflection at its surfaces. We also model and improve an integrating sphere setup to perform reliable measurements. Altogether, it permits achieving simple but general conclusions for samples with arbitrary shape or spatial distribution, from weak to highly absorbing, expanding the applicability of quantitative absorption spectroscopy. Finally, we validate it by measuring different sample formats made of PMMA: a cube, groups of granules and injection molding loose parts. The absorption coefficient of PMMA varies near three orders of magnitude in the explored range (380-1650 nm).

Item Type:Article
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Received: 28 Apr 2021 / Revised: 21 Jul 2021 / Accepted: 25 Jul 2021 / Published: 2 Aug 2021.
© 2021 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.

Uncontrolled Keywords:Absorption spectroscopy; Granulation; Absorption co-efficient; Arbitrary shape; Homogeneous samples; Integrating spheres; Light fields; Randomly distributed; Reliable measurement; Three orders of magnitude; Injection molding; Tunable Lasers; Trace Gas
Subjects:Sciences > Physics > Materials
Sciences > Physics > Optics
Medical sciences > Optics > Optical materials
ID Code:67954
Deposited On:20 Dec 2021 14:50
Last Modified:20 Dec 2021 15:13

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