The role of interface effects on the reflection of circularly polarised light from the thin-film structure of scarabus beetles

Many scarabus beetles, such as Gymnopleurus virens exhibit exceptionally bright iridescent colours caused by a Bragg resonance in the thin-layered structure of the exocuticle. These layers are rotated by a small angle with respect to each other resulting in a helcoidal stack, which reflects circularly polarised light with the same sense of rotation as that of the stack. Previous work assumed a smooth chiral structure, but in this work we explicitly include the effect of discrete layers and twist angles and investigate the effect of different layer densities on the reflectance spectrum. By comparing modelled results to experimentally recorded spectra it is possible to estimate the actual layer density found in this scarabus beetle. Copyright (C) 2008 John Wiley & Sons, Ltd.