Peacock feathers are greatly admired for their bright iridescent colors, but it turns out they can also emit laser light when dyed multiple times, according to a paper published in the journal Scientific Reports. Per the authors, it’s the first example of a biolaser cavity within the animal kingdom.
As previously reported, the bright iridescent colors in things like peacock feathers and butterfly wings don’t come from any pigment molecules but from how they are structured. The scales of chitin (a polysaccharide common to insects) in butterfly wings, for example, are arranged like roof tiles. Essentially, they form a diffraction grating, except photonic crystals only produce certain colors, or wavelengths, of light, while a diffraction grating will produce the entire spectrum, much like a prism.
In the case of peacock feathers, it’s the regular, periodic nanostructures of the barbules—fiber-like components composed of ordered melanin rods coated in keratin—that produce the iridescent colors. Different colors correspond to different spacing of the barbules.
Both are naturally occurring examples of what physicists call photonic crystals. Also known as photonic bandgap materials, photonic crystals are “tunable,” which means they are precisely ordered in such a way as to block certain wavelengths of light while letting others through. Alter the structure by changing the size of the tiles, and the crystals become sensitive to a different wavelength. (In fact, the rainbow weevil can control both the size of its scales and how much chitin is used to fine-tune those colors as needed.)
Even better (from an applications standpoint), the perception of color doesn’t depend on the viewing angle. And the scales are not just for aesthetics; they help shield the insect from the elements. There are several types of manmade photonic crystals, but gaining a better and more detailed understanding of how these structures grow in nature could help scientists design new materials with similar qualities, such as iridescent windows, self-cleaning surfaces for cars and buildings, or even waterproof textiles. Paper currency could incorporate encrypted iridescent patterns to foil counterfeiters.
