Circularly polarized reflection from the scarab beetleChalcothea smaragdina: light scattering by a dual photonic structure
Abstract
Helicoidal architectures comprising various polysaccharides, such as chitin and cellulose, have been reported in biological systems. In some cases, these architectures exhibit stunning optical properties analogous to ordered cholesteric liquid crystal phases. In this work, we characterize the circularly polarized reflectance and optical scattering from the cuticle of the beetleChalcothea smaragdina(Coleoptera: Scarabaeidae: Cetoniinae) using optical experiments, simulations and structural analysis. The selective reflection of left-handed circularly polarized light is attributed to a Bouligand-type helicoidal morphology within the beetle's exocuticle. Using electron microscopy to inform electromagnetic simulations of this anisotropic stratified medium, the inextricable connection between the colour appearance ofC. smaragdinaand the periodicity of its helicoidal rotation is shown. A close agreement between the model and the measured reflectance spectra is obtained. In addition, the elytral surface ofC. smaragdinapossesses a blazed diffraction grating-like surface structure, which affects the diffuse appearance of the beetle's reflected colour, and therefore potentially enhances crypsis among the dense foliage of its rainforest habitat.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Jun 16, 2017
- Source ID
- 10.1098/rsfs.2016.0129
Entities
People
- Bodo D. Wilts
- Ewan D Finlayson
- Luke T McDonald
- Pete Vukusic
Organizations
- Air Force Office of Scientific Research
- University College Cork
- University of Exeter
- University of Fribourg