Butterflies: Photonic Crystals on the Wing
Final rept. 15 Mar 2006-8 Jun 2007
GRONINGEN RIJKSUNIVERSITEIT (NETHERLANDS)
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In this project we focus on the optical properties of the wing scales of butterflies. The scales of numerous butterflies, specifically several Papilionidae and Lycaenidae, are very likely structured in the form of three-dimensional 3D photonic crystals to achieve vivid coloration of the wings. It is not uncommon for the same butterfly to have more than one type of structural color on the same wing. Current interpretations of the optics of butterfly wings are in terms of light reflected from volume diffraction gratings or multiple layers of thin films, but these explanations are far from satisfactory. The modeling of the 3D sub-wavelength structures has been hampered partly due to lack of detailed 3D structure characterization and measurement of the optical properties of the wing scales. We propose to use a combination of SEM and TEM to quantitatively determine the 3D structure of the wing scales. Angle-dependent reflection and transmission microspectrophotometry data obtained from isolated, single scales will be interpreted in terms of the photonic band structure of these complex 3D structures. The main objective is to demonstrate that the band folding and singularities at the intersecting points in k-space give rise to the angle and wavelength dependence of the light scattering from butterfly wing-scales. Most of the 3D structures observed in the scales of the wings of a butterfly appear to be much more complex than the photonic structures presently produced artificially. Since self-assembly methods are currently unable to reproduce these complex natural 3D structures, the butterfly wing-scales are expected to be extremely valuable for analyzing angle and wavelength dependent light scattering.