Bragg stacks with tailored disorder create brilliant whiteness

The scales of white beetles strongly scatter light within a thin disordered network of chitin filaments. There is no comparable artificial material achieving such a high scattering strength within a thin layer of low refractive index material. Several analyses investigated the scattering but could not explain the underlying concept. Here a model system is described, which has the same optical properties as the white beetles' scales in the visible wavelength range. With some modification, it also explains the behavior of the structures in the near infrared range. The comparison of the original structure and the model system is done by finite-difference time-domain calculations. The calculations show excellent agreement with the beetles' scales with respect to the reflectance, the time-of-flight, and the intensity distribution in the far-field.