A laser made from peacock feathers

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Many people know that peacock feathers shimmer excitingly in the light. But the fact that the feathers emit laser light after targeted excitation is a novelty. A team of researchers from Florida Polytechnic University has demonstrated that tiny, reflective structures in the eye of peacock feathers can focus light into a laser beam. The results were published in the journal Scientific Reports.

Basic building blocks of a laser

The basic building block for a laser is a so-called optically active medium, i.e., a material whose atoms or molecules can be excited into a higher-energy state by light. In the case of so-called dye lasers, these are usually fluorescent dyes.

The active medium is excited using a suitable light source: the electrons change from a low-energy state to a higher-energy state in a targeted manner. The aim is so-called population inversion – a state in which there are more electrons at the higher energy level than at the lower one.

When the particles return to their energetically more favorable state, they emit the excess energy in the form of photons. These stimulate other particles to also emit photons. A resonator amplifies this process and bundles the resulting avalanche of light into a focused laser beam.

A resonator from nature

In a conventional laser, the resonator consists of specifically arranged mirrors. In nature, however, microscopic structures can also produce a similar effect. This is the case in peacock feathers. Iridescent shades of color are not produced here with the help of pigments but are created due to ordered microstructures inside the feather that reflect the light in a certain way. This results in bright blue and green tones.

The research team dyed the feathers several times with the dye rhodamine 6G – a well-known laser medium for dye lasers – and then excited them with a solid-state laser.

The researchers were able to observe that differently colored regions of the feather emit laser radiation in two wavelengths and thus generate a yellow-greenish laser beam. Although this was not visible to the naked eye, it could be detected with measuring devices.

Mechanism unclear

Although the different parts of the spring shimmered in different colors and therefore presumably differed in their microstructure, they emitted laser light of the same wavelength. “The results suggest a critical structure inside the feathers that persists across different color regions of the eyespot,” the authors write in the study. These are presumably not the same structures that are responsible for the iridescent colors in the peacock eye.

The team was unable to identify exactly what the macrostructures that act as laser resonators look like. Thus, a conclusive explanation for the observed effect is still missing. Nathan Dawson, co-author of the study, suggested to Science that protein granules or similar small structures inside the feathers could act as a laser cavity.

Matjaž Humar, a biophotonics researcher at the University of Ljubljana, also told Science that the experiment was “a fascinating and elegant example of how complex biological structures can support the generation of coherent light.”

Dawson and his colleague believe their work could one day lead to the development of biocompatible lasers that could be safely incorporated into the human body for sensing, imaging, and therapeutic purposes.

(spa)