Within the diverse order of beetle species that produce color through structural coloration, some beetles produce light with a strong left-handed circular polarization caused by a chiral structure...Show moreWithin the diverse order of beetle species that produce color through structural coloration, some beetles produce light with a strong left-handed circular polarization caused by a chiral structure in their outer shells. From an evolutionary perspective, there should be no substan- tial benefit to left-handed over rather-handed polarization. This raises the question why no beetles have been found showing right-handed polarization. Large-scale beetle surveys are required to investigate this question further. A systematic beetle classification scheme based on polarization would aid in such a survey and highlight species with interesting optical prop- erties for further investigation. To this end we constructed a setup capable of measuring the Stokes parameters of a beetle specimen for angles of incidence and observation. We tested this setup on the beetle species protaetia speciosa jousselini and verified that the setup produces accurate results. We are however sceptical this method will result in identifying beetle-specific Stokes parameters, as their values vary with respect to both location on the beetle cuticle as well as observational angles. Furthermore we provide quantitative evidence for earlier re- ported inversion of the polarization handedness in beetle species jousselini at large angles of observation. We detect such inversion at angles of observation of at least 70◦.Show less
Structural color in insects is a well-known topic that has been studied intensely in the past decades with the progress in computational tools. These studies are mostly limited to specific species...Show moreStructural color in insects is a well-known topic that has been studied intensely in the past decades with the progress in computational tools. These studies are mostly limited to specific species and largely ignore the role of polarization. In this thesis we report a preliminary characterization of a setup that can measure the angle and polarization dependent reflection and transmission spectrum of a single Morpho menelaus butterfly scale or the local polarization dependent reflection spectra of beetle. The beam waist of white light in this setup can be as small as 40um, sufficient to address the spectrum of individual butterfly scales. The reflection of beetles is of particular interest. Reports in literature show that many beetles reflect only left circular polarized light that might be linked to the homo-chirality of nature in general and chitine molecules in particular. We build a theoretical model to explain these properties and compare our model to the results of Lowrey et al. for the Cetonischema jousselini at normal incidence. An extension of the model to other angles of incidence confirms that some right circular polarized signals can be observed for angle of incidence beyond 40 providing a basis for the observations of right circular reflection in the Cetonischema jousselini reported by Haged¨ us et. al.. The calculated spectra (elements of a Mueller matrix) are converted to RGB values as a function of angle of incidence to compare the calculations to images of beetles taken through circular polarizers with a commercial camera.Show less
