This schematic illustrates the novel nanosheet with three parallel segments created by the researchers, each supporting laser action in one of three elementary colors. The device is capable of lasing in any visible color, completely tunable from red, green to blue, or any color in between. When the total field is collected, a white color emerges. Credit: ASU/Nature Nanotechnology
More luminous, energy efficient than LEDs, white lasers look to be the future in lighting and Li-Fi, light-based wireless communication. Arizona State Uni researchers proved semiconductor lasers can emit over the full visible color spectrum: necessary to produce a white laser.
They created a novel nanosheet – thin layer of semiconductor ~1/5 of the thickness of human hair in size -with 3 parallel segments, each supporting laser action in 1 of 3 elementary colors. The device is capable of lasing in any visible color, completely tunable from red, green to blue, or any color in between. When the total field is collected, a white color emerges.
The tech advance puts lasers one step closer to being a mainstream light source and potential replacement or alternative to LEDs. Lasers can potentially provide more accurate and vivid colors for displays like computer screens and televisions. Ning’s group showed their structures could cover as much as 70% more colors than current display standard.
>> Another important app is visible light communication in which the same room lighting systems could be used for both illumination and communication. Called Li-Fi, as opposed to Wi-Fi using radio waves. Li-Fi could be >10X faster than current Wi-Fi, and white laser Li-Fi could be 10 – 100X faster than LED based Li-Fi under development.
The main challenge, lay in how light emitting semiconductor materials are grown and emit light of different colors. Semiconductor usually emit light of a single color- blue, green or red- determined by a unique atomic structure and energy bandgap. The most desired solution is a single semiconductor structure that emits all needed colors. They turned to nanotechnology to achieve this. The key is that at nanometer scale larger mismatches can be better tolerated than in traditional growth techniques for bulk materials. High quality crystals can be grown even with large mismatch of different lattice constants.
Blue, necessary to produce white, proved to be a greater challenge with its wide energy bandgap and very different material properties . They created the required shape first, and then convert the materials into the right alloy contents to emit the blue color. “…our unique growth strategy is the first demonstration of an interesting growth process called dual ion exchange process that enabled the needed structure.”
>>Significant obstacles remain to make white lasers applicable for real-life lighting or display apps. A crucial next steps is to achieve the similar white lasers under the drive of a battery. In this study, they used a laser light to pump electrons to emit light. This demonstrates the key 1st material requirement and will lay the groundwork for the eventual white lasers under electrical operation.
http://fullcircle.asu.edu/research/asu-engineers-demonstrate-the-worlds-first-white-lasers/
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