Scarab beetles can help scientists understand light polarization mechanisms
Scarab beetles can help scientists understand light polarization mechanisms lead image
The cuticle of the golden scarab beetle Chrysina resplendens has unique optical properties that have inspired biomimetic applications ranging from optical filters to phase retardation in lasers. It acts as a circular Bragg reflector, bouncing both left- and right-handed circularly polarized light off its body with high reflectance. To better understand these polarization properties, Mendoza-Galván et al. have modeled the structure of the cuticle of C. resplendens.
The beetle’s cuticle is a multilayer unit with a total thickness of about 20 micrometers. Beneath a waxy top is the exocuticle, which comprises of a birefringent layer sandwiched between two helicoidal layers. The sandwiched birefringent structure mirrors that of a circular Bragg reflector and is responsible for many of the optical properties of C. resplendens.
When light hits the cuticle, the outer helicoidal layer reflects left-handed components back but allows right-handed components through. As this right-handed circularly polarized light crosses the birefringent layer, it acquires an angle- and wavelength-dependent phase shift, which partially reverses its handedness. The resulting left-handed component then reflects off the lower helicoidal layer and gains an additional phase shift on its way back through to join the reflected beam.
Different reflectance behavior is observed in different wavelength regions, and varying quantities of uric acid in the birefringent material are likely responsible for variations in reflectance between beetles.
Though studies of the complex architecture of C. resplendens may produce additional biomimetic technologies, the purpose this polarization property serves for the beetle is relatively unknown. “There is very little information about which role these structure play in nature,” said author Arturo Mendoza-Galván. “A few attempts to study intraspecies communication have been done, but they are not conclusive.”
Source: “Mueller-matrix modeling of the architecture in the cuticle of the beetle Chrysina resplendens,” by Arturo Mendoza Galván, Kenneth Järrendahl, and Hans Arwin, Journal of Vacuum Science & Technology B (2019). The article can be accessed at https://doi.org/10.1116/1.5122824 .
