Magazine article American Scientist

An Unusual Shimmer

Magazine article American Scientist

An Unusual Shimmer

Article excerpt

To examine the outer shells, or cuticles, of shiny beetles, scientists can view them through filters like those found in modem 3D-movie glasses, which use both left- and right-handed circularly polarized filters (as the diagram below illustrates), one type of filter for each eye. Some shiny beetles reflect left-handed circularly polarized light, so although they still appear shiny through the left-handed filter, the right-handed filter eliminates the shiny color, allowing for closer examination. But the golden scarab beetle, Chrysina resplendens (pictured below), is different: It has a structural design that enables it to reflect both left- and right-handed circularly polarized light, and at roughly the same intensity.

"It is unclear whether any other species of beetle or animal concurrently reflects left-handed and right-handed circularly polarized light," says Pete Vukusic, who researches biophotonics at the University of Exeter in the United Kingdom. "If someone in a company were to design this, it would be a stunning innovation."

C. resplendens can reflect both types because it has a special layer in its cuticle that appears to work as a half-wave plate, transforming left-handed circularly polarized light into the right-handed circularly polarized light. It's particularly innovative because C. resplendens has the same structures as the thousand other beetle species known to reflect left-handed circularly polarized light. It just has two such structures, separated by that special layer.

"This complex structure is very much of interest," says Ewan Finlayson, because it could inform "a potential suite of novel optical components." Finlayson is first author of the paper describing the work that he, Vukusic, and Luke McDonald published in the June issue of the journal of the Royal Society Interface.

To examine that complex structure, the team employed the high-magnification imaging techniques of transmission electron micrography and scanning electron microscopy. Preparing the cuticle sample using accepted techniques resulted in a little shrinkage but did not otherwise affect the material's structure. After analyzing the physical layers, measuring optical reflectance, and then creating computer simulations to model that reflectance, the team suggested a hypothesis for how light passes through and is reflected by C. …

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