Polarized reflection and nanostructure in scarab beetles studied by spectroscopic Mueller-matrix ellipsometry
2012 (English)Conference paper, Abstract (Other academic)
Michelson showed one hundred years ago that the scarab beetle Chrysina resplendens reflects near-circular polarized light . More recent Mueller-matrix methodology has been employed to detail polarization phenomena in the exoskeleton of beetles [2,3]. The polarization is in a majority of cases left-handed but also right-handed polarization has been found. In addition these beetles may exhibit beautiful structural colors. Such structures may find use in many applications and a major motivation for detailed studies of natural photonic structures is that they inspire to biomimetic applications. Here we apply spectroscopic Mueller-matrix ellipsometry on scarab beetles with objective to model natural photonic nanostructures and to describe reflection properties in terms of polarization parameters and degree of polarization.
The studied beetles are from the following subfamilies: Cetoniinae (Cetonia aurata and Coptomia laevis); Rutelinae (Chrysina argenteola and Chrysina resplendens); and Melolonthinae (Cyphochilus insulanus). A dual rotating compensator ellipsometer (RC2, J. A. Woollam Co., Inc.) is used to record normalized Mueller-matrix spectra in the spectral range 300 – 900 nm at angles of incidence in the range 20-70º.
From Mueller-matrix data one can determine so called derived parameters of the reflected light including azimuth and ellipticity of its polarization ellipse and the degree of polarization. The variation of these parameters with wavelength and angle of incidence are presented for a selection of the scarab beetles above. Examples of both left-handed and right-handed polarization are shown for narrow-band and wide-band reflecting beetles and the importance of degree of polarization will be discussed.
Structural modeling is presented on Cetonia aurata to demonstrate that structural parameters can be extracted by advanced modeling of Mueller-matrix data. Cetonia aurata has a metallic shine and if illuminated with unpolarized white light it reflects left-handed polarized green light as revealed by a non-zero Mueller-matrix elements m14 and m41 in the green spectral region. At near-normal incidence the polarization can be almost circular. A model based on a twisted lamella structure, also called Bouligand structure, is used to model this chiral nanostructure. The obtained model parameters are the spectral variation of the refractive index of the birefringent lamellas and the pitch. The model also includes a dielectric surface layer.
Keywords: Mueller-matrix ellipsometry; scarab beetles; natural nanostructures; circular polarization
- Michelson, A. A. “On Metallic Colouring in Birds and Insects,” Phil. Mag. 21 (1911) 554-567
- Arwin, H., Magnusson, R., Landin, J., Järrendahl, K., “Chirality-induced polarization effects in the cuticule of scarab beetles: 100 year after Michelson”, Phil. Mag. 92 (2012) 1583-1599
- Hodgkinson, I., Lowrey, S., Bourke, L., Parker, A., McCall, M. W., “Mueller-matrix characterization of beetle cuticle polarized and unpolarized reflections from representative architectures”, Appl. Opt. 49 (2010) 4558-4567
Place, publisher, year, edition, pages
Mueller-matrix ellipsometry; scrab beetles; natural nanostructures; circular polarization
IdentifiersURN: urn:nbn:se:liu:diva-86501OAI: oai:DiVA.org:liu-86501DiVA: diva2:578303
XXI International Materials Research Congress (IMRC 2012), August 12 - 17, 2012, Cancun, Mexico
FunderSwedish Research Council, 621-2011-4283