Polarization resolved hyperspectral imaging of the beetle Protaetia speciosa jousselini

TL;DR

This study uses hyperspectral polarization imaging to analyze the chiral optical properties of the beetle Protaetia speciosa jousselini, revealing how its structural coloration relates to chiral photonic structures and their variations.

Contribution

It introduces hyperspectral polarization imaging of a beetle's structural color, providing detailed analysis of its chiral Bragg reflection and spectral properties.

Findings

Strong left-handed chiral Bragg reflection observed.

Reflection spectrum width characterized by a chiral photonic strength parameter.

Variation in reflectivity linked to thickness changes in the chiral Bragg reflector.

Abstract

Understanding and classifying chiral structural color of scarab beetles across the phylogenetic tree is an important scientific tool to explore the origins of the homochiral optical response in biological structures with a potential relation to the homochirality of (chitin) molecules. We report hyperspectral polarization resolved images of the scarab beetle \textit{Protaetia speciosa jousselini} (Gory \& Percheron, 1833) and resolve the state of polarization as a function of both position (spatial resolution of $\sim$20 $\mu$m $\times$ 10 $\mu$m) and wavelength (spectral resolution of 5.5 nm). We observe a strong left-handed chiral Bragg reflection and analyze the center wavelength and width of the spectrum. The reflection and state of polarization scale with the center wavelength of the Bragg reflection, while the relative width of reflection spectrum is characterized by a chiral photonic strength parameter $\psi_C \approx 0.14$ that is independent of the reflected color and position. Based on the self-similarity of the reflection spectra we interpret variation in reflectivity as variations in the thickness of the chiral Bragg reflector across the beetle.