The scientific study of structural colour in nature dates back over 300 years. The structural
colours being observed are a result of millions of years of evolution. It occurs in many different
forms in nature from diffraction gratings to interference from multi layered structures and from
plants to cephalopods.
This thesis focuses on the near circularly polarised (CP) reflection from the helicoidally arranged
chitin within the shells of selected beetles from the Scarabaeoidae superfamily. An experimental
setup was refined in order to measure broadband CP light in reflection from the beetles. A large
variation in the left CP reflection was seen both within and between species, genera, subfamilies
and families. This included broadband reflection from silver coloured beetles to narrower
reflection of dominant green colour (other colours were observed). A wide variety of spectral
shapes were observed including single wavelength peaks, multiple oscillations and peaks far
apart. In the Chrysina genus several new species were observed to reflect both right and left CP
light.
Several perturbations of the CP reflection were modelled based upon Berreman calculus.
Further to the CP measurements electron, atomic force and scanning near-field optical
microscope images were taken of both the helicoidal structure and surface of the beetles.
A fuller description of the polarisation of the reflected near CP light from the beetles’ shells was
obtained using a broadband Mueller Matrix (MM) ellipsometer, which was built and designed
using liquid crystal variable retarders. From the MMs, the ellipticity, the degree of polarisation
and azimuth angle were calculated. As with the CP measurements large variations were
observed from highly polarised metallic to less polarised matt specimens.
This study of the beetle optical properties will help to inspire the design of various optical
devices as well as the further biological investigation into beetles’ polarised vision.