Fibre-Optical Light Scattering Technology in Polar Bear Hair: A Re-Evaluation and New Results

Abstract

In very early studies, the function of the transparent hair of polar bears with their light scattering hollow core has been associated with fibre-optical properties. Critics, arguing that the distance propagated by the light is too short, later denied this. New spectroscopic, microscopic, and laser-optical studies explain the contradiction. The light harvesting mechanism can only be understood as a synergetic cooperation of many of the animal`s hairs. Light is coupled into the hair`s fibre via a scattering process for a short distance where soon after it is coupled out by a subsequent scattering process, just to be coupled again into a neighbouring hair and so on until the light is dissipated into heat or absorbed by the bear`s black skin. In the meanwhile, a small percentage of the incident light is backward scattered. As a result, the pelt`s transparent hairs appear white, while absorbing most of the incident radiation. Moreover, the solar optical technology includes a complementary strategy: the IR -radiation of body`s heat, between 8000 and 12000 nm, is effectively trapped by an analogue mechanism. This is supported by the high absorptive capacity of the fur and the absence of any significant spectroscopic feature in the entire spectral region. The polar bear evolved an efficient optical nano-technology for energy harvesting and energy conservation. Challenges for a biomimetic energy technology based on Mie scattering are discussed.