From Event: SPIE Optical Engineering + Applications, 2019
Beetles of the families Scarabaeidae and Hybosoridae display left-handed circular polarization due to the Bouligand arrangement of chitin fibers in their cuticle. We intend to verify and understand, or disprove, the apparent and hitherto unexplained universality of left-handed polarization in beetles that exhibit circular polarization. We here report the first results of our ongoing massive survey of one of the largest beetle collections in the world, covering ±10.000 beetle genera. To facilitate the scanning of museum drawers full of beetles, drawers were placed in a purpose-built setup and automatically photographed in RGB colors through polarization filters mounted on a motorized wheel. A total of 6 photographs were taken, through left- and right-handed circular polarization filters, and four linear polarization filters mounted at 0, 90, 45, and -45 degrees. From these, the full Stokes parameters were calculated across the drawer. Images were segmented to obtain polarization parameters representing individual insects. Taxonomic information was obtained for each drawer, by automatically reading the database accession number. Specimens showing circular polarization in taxa for which this has hitherto not been studied are selected to be studied in more detail later, using a custom designed spectropolarimetric integral-field unit. Polarization can then be analyzed as a function of wavelength, resulting in both detailed hyperspectral imaging data and fully resolved Stokes parameters per spectral bin. Our two-stage high-throughput optical screening approach allows for bioprospecting for biophysical properties of valuable and potentially irreplaceable museum specimens, such as type specimens, or specimens of rare or even extinct species.
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Arie van der Meijden, Drisyaman Kashyap, Olivier Burggraaff, Menno Schilthuizen, and Frans Snik, "Testing universal chirality in photonic nanostructures of beetles through a large-scale polarimetric survey (Conference Presentation)," Proc. SPIE 11132, Polarization Science and Remote Sensing IX, 111320D (Presented at SPIE Optical Engineering + Applications: August 14, 2019; Published: 10 September 2019); https://doi.org/10.1117/12.2529541.6084693036001.