Circularly polarized reflection from the scarab beetleChalcothea smaragdina: light scattering by a dual photonic structure

ArticleThis is the author accepted manuscript. The final version is available from Royal Society via the DOI in this record.Helicoidal architectures comprising various polysaccharides such as chitin and cellulose have\udbeen reported in biological systems. In some cases, these architectures exhibit stunning optical\udproperties analogous to ordered cholesteric liquid crystal phases. In this work, we charac-\udterise the circularly polarised re\udectance and optical scattering from the cuticle of the beetle\udChalcothea smaragdina (Coleoptera: Scarabaeidae: Cetoniinae) using optical experiments, sim-\udulations and structural analysis. The selective re\udection of left-handed circularly polarised light\udis attributed to a Bouligand-type helicoidal morphology within the beetle's exocuticle. Using\udelectron microscopy to inform electromagnetic simulations of this anisotropic strati ed medium,\udthe inextricable connection between the colour appearance of C. smaragdina and the periodic-\udity of its helicoidal rotation is shown. A close agreement between the model and the measured\udre\udectance spectra is obtained. In addition, the elytral surface of C. smaragdina possesses\uda blazed di raction grating-like surface structure, which a ects the di use appearance of the\udbeetle's reected colour, and therefore potentially enhances crypsis amongst the dense foliage\udof its rainforest habitat.This work was financially supported by the National Centre of Competence in Research Bio-\udInspired Materials and the Ambizione program of the Swiss National Science Foundation SNSF\ud(PZ00P2 168223, to BDW)