Investigating the Iridescence and Polarisation Properties of Butterflies and Beetles

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 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...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

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Investigating the Iridescence and Polarisation Properties of Butterflies and Beetles