Cao’s team drilled holes in a 190-nanometer-thin sheet of gallium arsenide, a special sort of semiconductor that transmits light efficiently and is commonly used in optics. The holes were spaced between 235 and 275 nanometers apart. The material included a layer of equally spaced quantum dots, which emit lots of light when struck with one photon. When light entered the material, the physicists reasoned, it should bounce around between the holes long enough to make the quantum dots produce enough photons to start lasing.
When the researchers lit up the tiny wafer, it produced laser light with wavelengths of about 1,000 nanometers, in the near-infrared range of the electromagnetic spectrum. It was much more efficient than random lasers. The researchers also found that they could change the wavelength of the laser light by changing the spacing between the holes.
“Just like the birds, who can tune their short-range order to get different color from their feathers. We can do the same thing,” Cao said. Cao doesn’t have any particular applications in mind for this tunable, efficient laser. But she points out that by giving up on long-range order, her laser is much cheaper and easier to build than previous models. “We can have control, and it doesn’t have to be perfect,” she said. “That’s what we learned from nature.”
Cao and colleagues are now trying to use actual bird feathers as a template. They hope to embed tiny semiconductors in the air holes and dissolve away the keratin that holds them together. This might be an easier way to make lasers with extremely short wavelengths, in the blue or ultraviolet range.
It might be even more interesting to figure out how the birds build their feathers in the first place, said biologist Matt Shawkey of the University of Akron in Ohio. “Birds seem to do it very cheaply. They have thousands of these feathers,” he said. “If you can get these things to build themselves, taking the painstaking process out, then you’d barely have to put any energy and time into it. It would be really cool to see which parameters the birds are changing to get these feathers to self-assemble.”
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