peacock feathers

A peacock feather's colors are not solely derived from pigment, but are more likely driven by the structure of the feather.

This structure includes arrays on the barbules of the feather which are like twigs on the branches of the feather.





The figure on the right explains the different wavelengths measuring reflectivity in four regions of the peacock feather. The images below show the barbules at different magnifications to show variations in the filaments. Ultimately the difference we see is a result of reflections from the front and back of the feather structure acting like a Fabry-Perot interference (explained below) to enhance the color.

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Fabry-Perot Interferometer

This interferometer makes use of multiple reflections between two closely spaced partially silvered surfaces. Part of the light is transmitted each time the light reaches the second surface, resulting in multiple offset beams which can interfere with each other. The large number of interfering rays produces an interferometer with extremely high resolution, somewhat like the multiple slits of a diffraction grating increase its resolution.

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Beetles Use Nanostructures for Color

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."

"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."

"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."

"Researchers speculate that these beetles may even use such photonic complex substructures to communicate with each other via light or to ward off predators."

http://www.technologyreview.com/blog/editors/23881/