Talk:Chrysina resplendens

Explanation of golden iridescence in chrysina resplendens' exoskeleton

Shouldn't we include this information on how the scarab's iridescence works? It is a reserach paper by Ewan D. Finlayson, Luke T. McDonald and Pete Vukusic, published June 25, 2017 in the University of Exeter, and is titled Optically ambidextrous circularly polarized reflection from the chiral cuticle of the scarab beetle Chrysina resplendens.

The paper states that the ability to appear like pure solid gold is a result of intricate nano-structures in their chitin exoskeleton, whose spacing and repeating layers are found to vary over a specific range through the skeleton, which causes the simultaneous reflection of a range of visible colours of light. It is this that explains the exoskeleton's very bright reflection as well as golden hue. The nano-structured exoskeleton is composed of natural materials including chitin and various proteins, and in addition to their strong reflectiveness, the structures are remarkable in the way they manipulate the way that polarised light is reflected. They produce circularly-polarised light, where the orientation of the light's oscillations rotate as the light travels. The two possible directions of rotation of said light are referred to as "left-handed" and "right-handed" in the paper.

Text directly taken from paper:

While most species of Chrysina reflect only left-hand CP (LHCP) [1,23], C. resplendens is remarkable in that it also preserves right-hand CP (RHCP) upon reflection. The beetle may therefore be described as optically ambidextrous, which we define as having the ability to reflect both hands of CP. Caveney [8] characterized the structure experimentally and found that the birefringence is enhanced by the presence of uric acid. Two left-handed helicoidal regions were identified, separated by a ‘unidirectional layer’ of birefringent material in which the rotation of microfibril planes is interrupted (figure 1e,f). This layer forms a birefringent retarder that is analogous to the nematic liquid crystal phase and acts as a half-wave plate within the reflectance band. The RHCP reflectance was thus explained by a switch to LHCP on transmission through the unidirectional layer, followed by reflection by the second helicoid and a switch back to RHCP on the return pass through the retarder. Both helicoidal regions were found to be chirped, whereby the smoothly varying helicoidal pitch includes a range of dimensions, giving rise to broadband reflectance and therefore the appearance of a golden colour.

--Luka1184 (talk) 22:53, 12 May 2020 (UTC), edited 00:17 12 May 2020 (UTC)