The structural coloration mechanisms of Morpho butterfly wing scales
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Many bright colors in nature are generated by the optical effects of biological structures. These intricate structures, combined with the absorption and reflection effects of the chemical pigments within, provide the observed color with high visibility and some other startling optical properties. A prominent example comes from the iridescent colors observed on the wing scales of Morpho, a family of subtropical butterflies. Iridescent color refers to the color which changes with varying viewing angle. It is proposed that a layered structure alternating in refractive indices produces the observed colors on the butterfly wing scales, but this generalized idea does not explain some optical effects observed through a variety of methods. This research suggests that the structures in the lower lamina also contributes to the macroscopic optical effects. The observation methods used in this research include optical microscopy, spectroscopy, integrating sphere analysis, and scatterometry. The scatterometry visualizes the far field optical effects from all viewing angles simultaneously. Elementary explanations are proposed for the unexpected patterns observed in the experiments.