Modelling structural colour from helicoidal multi-layer thin films with natural disorder

A coupled mode theory based on Takagi-Taupin equations describing electromagnetic scattering from distorted periodic arrays is applied to the problem of light scattering from beetles. We extend the method to include perturbations in the permittivity tensor to helicoidal arrays seen in many species of scarab beetle and optically anisotropic layered materials more generally. This extension permits analysis of typical dislocations arising from the biological assembly process and the presence of other structures in the elytra. We show that by extracting structural information from transmission electron microscopy data, including characteristic disorder parameters, good agreement with spectral specular and non-specular reflectance measurements is obtained.

Automated summary

This paper discusses the application of a coupled mode theory based on Takagi-Taupin equations to describe electromagnetic scattering from distorted periodic arrays, particularly in the context of light scattering. By extending the method to include perturbations in the permittivity tensor, the approach can analyze various shapes of arrays and materials, and achieve good agreement with reflectance measurements by extracting structural information from microscopy data.