Since being invented in 1960, lasers have been put to use in all sorts of applications, from computers and printers to fiber optics and surgery. But for this whole period there was one thing in particular that lasers simply could not do: produce white light. Now, a team of researchers has finally announced that they’ve managed just that, creating a device that can emit in any color across the visible spectrum, a requirement for white lasers.
Normally, lasers can only produce a single wavelength, meaning that they are restricted to one particular color of light. This color is dictated by the structure of the semiconductor, which is “usually a solid chemical element or compound arranged into crystals,” and is what produces the light when a voltage is applied to it.
Researchers have previously demonstrated that by combining four separate lasers of different colors, they can produce white light that the human brain can process as a single color. But until now, it’s not been possible to do this with a single laser. The team of researchers from Arizona State University have been able to create a semiconductor that has three different sections, which, when stimulated, emit red, green, and blue, and thus combine to form white.
“Our goal is to achieve a single semiconductor piece capable of laser operation in the three fundamental lasing colors. The piece should be small enough, so that people can perceive only one overall mixed color, instead of three individual colors,” said Fan Fan, one of the authors of the paper published in Nature Nanotechnology. “But it was not easy.”
To create the semiconductor, which is a nanosheet that is roughly one thousandth of the thickness of a human hair, the researchers had to work out a way to make it with a structure that emits multiple wavelengths. They were previously able to show that this was possible with red and green, but found it difficult to add blue to the mix.
“We have struggled for almost two years to [make] blue emitting materials in nanosheet form, which is required to demonstrate eventual white lasers,” said Sunay Turkdogan, another of the researchers. But eventually they cracked it by combining zinc, calcium, sulfur, and selenium to make an alloy that emitted the three separate wavelengths of red, green, and blue at the same time.
This milestone puts lasers closer to eventually becoming a mainstream light source. Brighter and more energy efficient, they could replace LEDs, and even be used to make more accurate and vivid colors on computer and television screens. In addition, technology is under development to create light-based wireless communication, known as Li-Fi, which could potentially be more than 10 times faster than Wi-Fi.
Center image: The separate colors red (R), green (G), and blue (B), shown in different combinations, and finally all together forming a white laser. Credit: ASU/Nature Nanotechnology.