World's first white laser demonstrated

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This schematic illustrates the novel nanosheet with three parallel segments created by the researchers, each supporting laser action in one of three elementary colors(Credit: ASU/Nature Nanotechnology)

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Incandescent bulbs, LEDs, and CFLs may soon have to budge up because a new lighting technology is in town – white lasers. Using nanotechnology to create a bespoke semiconducting material, a team of scientists at Arizona State University (ASU) has developed a laser that can produce white light that is brighter and more efficient than LEDs.

Lasers are an ironic technology. Invented in 1960, the laser was hailed as a solution in search of a problem with only two obvious areas of application – death rays and lighting. Today, lasers run everything from DVD players to the internet, while the death rays are only just coming on line and the lighting, which is also new on the scene, is largely restricted to headlamps. The latter, in the case of Audi's laser headlamps, don't use white lasers as such, instead combining lensed blue lasers with LEDs.

At first glance, lasers seem like a great idea for lighting. They're intensely bright, efficient, and can form a beam that can travel for millions of miles and only spread out a few meters. There's a problem though – lasers cannot generate white light.

In 2011, Sandia National Laboratory produced white light by combining four large lasers into a single beam, but this was only a proof of concept demonstration and not a practical system.

The breakthrough came from ASU's Ira A. Fulton Schools of Engineering, where scientists came up with a semiconductor laser that can operate across the entire visible color spectrum. Normally, semiconductors only produce a single wavelength of light, but the ASU team developed a sheet of nanoscale semiconductor based on a quaternary alloy of ZnCdSSe, which is formed into three segments. These generate red, green, and blue lasers that combine to create a pure white light.

The team achieved this by adjusting the lattice pattern of the material, so the “lattice constant” or distance between the atoms in the pattern is set to produced the desired area. According to team member Zhicheng Liu, the tricky bit was to make sure the semiconductor crystals were of high enough quality and the lattices uniform across a given area. Getting the material to shine blue was the most difficult challenge, which was overcome by using nanotechnology to create the desired lattice first, then prompting it into the right alloy composition. The result was a single material with three different lattices and compositions.

The ASU team sees several applications for the white laser once it becomes practical. The most obvious is in lighting. The new laser can not only generate white light, but is also completely tunable across the entire spectrum – allowing it to radiate any desired color – and is brighter and more efficient than LEDs. Another application is in televisions and computer monitors. According to the researchers, the laser has a 70 percent greater color range that is more accurate and vivid. In addition, it could be used for a light-based version of Wi-Fi (or Li-Fi). Such a system would be ten times faster than Wi-Fi and ten to 100 times faster than experimental LED systems.

The white laser is currently in proof of concept form and several hurdles need to be overcome before the technology is practical. According to the team, the biggest of these is making it run off a battery. In its present form, the material runs off a separate laser, which pumps electrons into the semiconductor.

The team's results were published in Nature Nanotechnology.

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