The effect of wool fibre medullation on diameter measurement in the expanding beam Laserscan has been investigated. A range of single fibres of diameter from 10 to 75 um was used to investigate differences in the Laserscan optical response to normal and medullated wool. The concept of mean `Fresnel diameter' is introduced to account for the variation in diameter along the fibre axis. Measruements on unmedullated and highly medullated wool fibres show no discernable systematic differences, and are in good agreement with Fresnel diffraction theory.
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