Mr. Ville T. Keränen Profile

Ville T. Keränen

at Providence St Vincent Medical Ctr

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Proceedings Article | 25 February 2010 Paper

Polyurethane phantoms with homogeneous and nearly homogeneous optical properties

Ville Keränen, Anssi Mäkynen, Amanda Dayton, Scott Prahl

Proceedings Volume 7567, 75670D (2010) https://doi.org/10.1117/12.843609

KEYWORDS: Polyurethane, Optical properties, Scattering, Absorption, Transmittance, Particles, Calibration, Integrating spheres, Microscopes, Titanium dioxide

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Phantoms with controlled optical properties are often used for calibration and standardization. The phantoms are typically prepared by adding absorbers and scatterers to a clear host material. It is usually assumed that the scatterers and absorbers are uniformly dispersed within the medium. To explore the effects of this assumption, we prepared paired sets of polyurethane phantoms (both with identical masses of absorber, India ink and scatterer, titanium dioxide). Polyurethane phantoms were made by mixing two polyurethane parts (a and b) together and letting them cure in a polypropylene container. The mixture was degassed before curing to ensure a sample without bubbles. The optical properties were controlled by mixing titanium dioxide or India ink into polyurethane part (a or b) before blending the parts together. By changing the mixing sequence, we could change the aggregation of the scattering and absorbing particles. Each set had one sample with homogeneously dispersed scatterers and absorbers, and a second sample with slightly aggregated scatterers or absorbers. We found that the measured transmittance could easily vary by a factor of twenty. The estimated optical properties (using the inverse adding-doubling method) indicate that when aggregation is present, the optical properties are no longer proportional to the concentrations of absorbers or scatterers.

Proceedings Article | 5 June 2008 Paper

Double integrating sphere system for optical parameter determination of industrial suspensions

Ville T. Keränen, Anssi Mäkynen

Proceedings Volume 7022, 70220T (2008) https://doi.org/10.1117/12.804056

KEYWORDS: Reflectivity, Optical spheres, Integrating spheres, Scattering, Transmittance, Optical properties, Optical testing, System integration, Absorption, Anisotropy

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The main objective of this study was to construct a double integrating sphere system and to verify its performance using Intralipid fat emulsion. The final goal was to be able to determine optical properties of various turbid suspensions with the proposed system. Online measurements even would have been possible as backscattering and forward scattering were measured simultaneously. The measured suspension was injected in a cuvette placed between two integrating spheres and illuminated with a laser through the first sphere. The diameter of the spheres was 8" and the diameter of the sample port could have been varied up to 2.5". The cuvette was made of plastic and optical grade glass and its diameter was sufficient to cover the sample port area. The sample thickness in the measurement cuvette was 5 mm. Optical powers were detected using fiber coupled photodiodes. There was one diode for each sphere and one for the unscattered light at the opposite end of the sphere system facing towards the laser. The measured optical powers were converted to absorption coefficient, scattering coefficient and if possible to anisotropy using an inverse adding-doubling method. The results measured for the Intralipid using the described system corresponded with those documented in published literature. A number of pulp samples with unknown optical properties were measured with encouraging results. However, the differences between different pulps and fillers are so small that, in the future, the focus will be in error source elimination to achieve reasonable accuracy.

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