Vanishing act: The jeweled beetle reflects a metallic green in regular light (left). It loses that reflection if a right circularly polarized light is used (right).
Courtesy of Science/AAAS
Many bright, iridescent beetles and butterflies get their brilliant colors not from pigments, but from the way tiny structures on their bodies reflect light. These structures have long been of interest to scientists, who hope to imitate these photon-controlling crystals to build better solar cells, sensors, and other optical devices–potentially even optical computer chips.
Researchers at the Georgia Institute for Technology have now taken a closer look at the exoskeleton of the jewel beetle–the details are published today in the journal Science. Previously, researchers had shown that the beetle reflects what appears to us as a shining green color in the form of leftward-circulating polarized light (as the light travels, its corresponding electric field rotates leftward). Shining only right-turning polarized light at the beetle causes it to lose its green color (see the pictures above).
The left-turning reflection occurs because of complex helical nanostructures in the beetle’s exoskeleton. Its exoskeleton is made up of hexagonal, pentagonal, and heptagonal cells containing yellow cones surrounded by green. Vivek Sharma, Mohan Srinivasarao, and others at Georgia Tech used confocal microscopy to show how tightly packed, concentric arcs (or spirals) on these cells look very similar to a type of liquid crystal. Because scientists already understand how liquid crystals form, this new association may help them understand how the insect’s optical structure self-assembles.
Last year I wrote about a Brazilian beetle that has an ideal photonic-crystal structure that researchers are trying to emulate. Researchers speculate that these beetles may even use such photonic complex substructures to communicate with each other via light or to ward off predators.