A Mueller matrix of a sample can be used to determine the polarization of reflected light for incident light with arbitrary polarization. The polarization can be quantified in terms of ellipticity, polarization azimuth and degree of polarization. We apply spectroscopic Mueller-matrix ellipsometry at multiple angles of incidence to study the cuticle of beetles and derive polarization features for incident unpolarized light. In particular we address chiral phenomena in scarab beetles, the origin of their structural colors and the observed high degree of circular polarization is discussed. Results from beetles in Scarabaeidae subfamilies Cetoniinae and Rutelinae are presented including specimens with broad-band silver-or gold-like colors with metallic shine as well as specimens with narrow-band green or red reflectors. The variation of polarization with angle of incidence and occurrence of both left-handed and right-handed polarization from a single species are presented. We also use Mueller-matrix thicknesses and optical properties. Interference oscillations in the observed spectra are due to allowed optical modes and we show how to develop a structural model of a cuticle based on this effect. Sum decomposition of Mueller matrices measured on a depolarizing cuticle of a beetle is briefly discussed.

Date Published: 26 March 2015
PDF: 13 pages
Proc. SPIE 9429, Bioinspiration, Biomimetics, and Bioreplication 2015, 942909 (26 March 2015); doi: 10.1117/12.2083032

Published in SPIE Proceedings Vol. 9429:
Bioinspiration, Biomimetics, and Bioreplication 2015
Akhlesh Lakhtakia; Mato Knez; Raúl J. Martín-Palma, Editor(s)