Azimuthal Scattering from Elliptical Hair Fibers

The appearance of hair follows from the small-scale geometry of hair fibers, with the cross-sectional shape determining the azimuthal distribution of scattered light. Although previous research has described some of the effects of non-circular cross sections, no accurate scatteringmodels for non-circular fibers exist. This article presents a scattering model for elliptical fibers, which predicts that even small deviations from circularity produce important changes in the scattering distribution and which disagrees with previous approximations for the effects of eccentricity. To confirm the model's predictions, new scattering measurements of fibers from a wide range of hair types were made, using a new measurement device that provides a more complete and detailed picture of the light scattered by fibers than was previously possible. The measurements show features that conclusively match the model's predictions, but they also contain an ideal-specular forward-scattering behavior that is not predicted and has not been fully described before. The results of this article indicate that an accurate and efficient method for computing scattering in elliptical cylinders-something not provided in this article-is the correct model to use for realistic hair in the future and that the new specular behavior should be included as well.