The First White Laser

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Image: Arizona State University/Nature Nanotechnology

Scientists and engineers at Arizona State University, in Tempe, have created the first lasers that can shine light over the full spectrum of visible colors. The device’s inventors suggest the laser could find use in video displays, solid-state lighting, and a laser-based version of Wi-Fi.

Although previous research has created red, blue, green and other lasers, each of these lasers usually only emitted one color of light. Creating a monolithic structure capable of emitting red, green, and blue all at once has proven difficult because it requires combining very different semiconductors. Growing such mismatched crystals right next to each other often results in fatal defects throughout each of these materials.

But now scientists say they’ve overcome that problem. The heart of the new device is a sheet only nanometers thick made of a semiconducting alloy of zinc, cadmium, sulfur, and selenium. The sheet is divided into different segments. When excited with a pulse of light, the segments rich in cadmium and selenium gave off red light; those rich in cadmium and sulfur emitted green light; and those rich in zinc and sulfur glowed blue.

The researchers grew this alloy in stages, carefully varying the temperature and other growth conditions over time. By controlling the interplay between the vapor, liquid, and solid phases of the different materials that made up this nano-sheet, they ensured that these different crystals could coexist.

The scientists can individually target each segment of the nano-sheet with a light pulse. Varying the power of the light pulses that each section received tuned how intensely they shone, allowing the laser to produce 70 percent more perceptible colors than the most commonly used light sources.

Lasers could be far more energy-efficient than LEDs: While LED-based lighting produces up to about 150 lumens per watt of electricity, lasers could produce more than 400 lumens per watt, says Cun-Zheng Ning, a physicist and electrical engineer at Arizona State University at Tempe who worked on the laser. In addition, he says that white lasers could also lead to video displays with more vivid colors and higher contrast than conventional displays.

Another important potential application could be "Li-Fi", the use of light to connect devices to the Internet. Li-Fi could be 10 times faster than today’s Wi-Fi, but "the Li-Fi currently under development is based on LEDs," Ning says. He suggests white-laser based Li-Fi could be 10 to 100 times faster than LED-based Li-Fi, because the lasers can encode data much faster than white LEDs.

In the future, the scientists plan to explore whether they can excite these lasers with electricity instead of with light pulses. They detailed their findings online 27 July in the journal Nature Nanotechnology.

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