Laser-emitting materials can be put onto nearly any surface through inkjet printers, which could lead to more-lifelike video displays, as well as unusual applications such as digital wallpaper, scientists say.
The lasers are made using liquid crystals, the same materials found in LCDs (liquid crystal displays) now common in laptop displays, flat-screen televisions and digital watches. Liquid crystals are a broad class of what are known as self-organized materials, whose ingredients naturally assemble themselves into orderly structures.
"Many biological materials — for example, DNA, cellular walls, soaps — exhibit self-organization and could be described as liquid crystals," said researcher Damian Gardiner at the University of Cambridge in England.
The researchers could print inks containing these liquid crystals as dots onto nearly any surface.
"We have looked at paper, plastic, metal, silicon, glass," Gardiner told TechNewsDaily.
To print these dots, the researchers used inkjet printers that heated ink to 203 degrees Fahrenheit (95 degrees Celsius), nearly the temperature of boiling water.
"Heating is used to reduce the viscosity of the material to allow printing; the viscosity is close to that of molasses at room temperature," Gardiner said. "We think using non-heated print heads would certainly be feasible with further work — for example, using a lower-viscosity liquid crystal. Hence, in principle at least, they could be deposited at home."
A laser commonly involves a chamber whose insides are lined with mirrors. Light is shined into this cavity and bounces back and forth off these mirrors. This space is also filled with a "gain medium," a substance that amplifies the amount of energy in this light. One of the mirrored sides in this chamber is partially transparent, allowing the laser beams inside to emerge.
The liquid crystal solution contains a fluorescent dye that behaves as the gain medium. It also possesses an additive that makes the crystals self-organize in a corkscrew-shaped manner. These spirals act as mirrors and determine the color of the lasers. By adding more additive, the emissions move to the blue; less additive shifts emissions to the red.
In experiments, researchers created lasers in dots just 10 microns thick and 300 microns wide. For comparison, a human hair is about 100 microns in diameter.
"Liquid crystal lasers have been around for the past decade or so, with significant amounts of research ongoing owing to their potential," Gardiner said. "However, our development — making them inkjet-printable — is a key step we feel in opening up completely new applications of lasers. For example, unlike existing technology, we could print arrays of lasers of different colors on the same, arbitrary surface."
Lasers are used in a huge, diverse range of applications, such as telecommunications and DVD players.
"In particular, many medical diagnostic tests use lasers," Gardiner said. "With our development, you could dramatically speed up such tests because analysis could be done very rapidly in a combinatorial type way — for example, arrays of 100 by 100 or more lasers on standard bio-assay arrays — but very inexpensively and possibly on a disposable basis if required."
Other applications could include video displays incorporating lasers, the team says.
"In some respects, lasers are ideal for displays," Gardiner said. "They can produce the best, most lifelike colors available, owing to their color purity … Our development could really help with the mass production of such systems."
One might even imagine creating wallpaper with these laser dots that broadcast data. "The wallpaper application is slightly wacky," Gardiner said.
The scientists detailed their findings online Aug. 24 in the journal Soft Matter.
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