Analysis of Mueller-matrix data from chiral structures in exoskeletons of scarab beetles
2012 (English)Conference paper, Abstract (Other academic)
Several species of scarab beetles exhibit extra-ordinary metallic-like structural colors. These color-generating structures also show complex polarization properties and unpolarized light can be reflected with near-circular polarization. Specimens of Cetonia aurata (Linnaeus, 1758) are here studied with a dual-rotating compensator ellipsometer using focusing probes. Mueller-matrix data are recorded with precision better than ±0.005 in the range 350 – 1000 nm for angles 20-60º. In a narrow spectral range in the green part of the spectrum, the Mueller-matrix elements m14 and m41 show large negative values and the reflected light is near-circular left-handed polarized. This effect originates from a chiral structure in the beetle exoskeleton. A twisted biaxial lamellae structure with a top dielectric layer is used in regression analysis to determine pitch of the helix and refractive indices of the chitin-based constituting materials. The applicability of this model to data from different scarab beetles is reviewed and it is found that the model show limitations for beetles with broad-band reflection, e.g. those with gold-like colors. For narrow-band optical features, the model provides an excellent fit for all 15 normalized Mueller-matrix elements over the full spectrum and angle of incidence range. Dispersion models like Cauchy, b-splines and oscillator-based models are employed for the biaxial layer and fit qualities for the tested models are compared.
Place, publisher, year, edition, pages
IdentifiersURN: urn:nbn:se:liu:diva-86592OAI: oai:DiVA.org:liu-86592DiVA: diva2:579201
E-MRS 2012 Spring meeting, May 14-18, 2012, Strasbourg, France
ProjectsNatural Photonic Nanostructures
FunderSwedish Research Council, 621-2011-4283