Lasers are everywhere -- in DVD players, fiber optic communications and even displays. They are so useful it would be great if they were flexible and easy to make, but that hasn't been the case, until now.
Researchers at the University of Cambridge in the U.K. have developed a way to print lasers on a variety of surfaces, using a printer not too far removed from the one on an average desktop.
The team, led by D.J. Gardiner of the Center for Molecular Materials for Photonics, used liquid crystals similar to those used in liquid crystal displays. With the right kind of stimulation, the molecules in liquid crystals emit laser light.
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The molecules are arranged in spiral patterns, which causes them to act as optical cavities. Optical cavities are one way to make laser light, because the cavity confines light in such a way that all the light waves are "in step," or coherent -- a laser beam. Because the liquid crystal molecules can change their arrangement, it's possible to change what wavelengths are reflected.
Ordinarily a lasing material has to be "pumped" with some external source of energy. In this case it's pumped with laser light. To get that final bit of "gain" a fluorescent dye is added to the liquid crystals, and it's that gain which produces the extra energy for the laser.
Gardiner told Discovery News that while it might seem odd to produce laser light with another laser, that can be more efficient than other methods. The ability to control what wavelength of laser light comes out by controlling the size of the spiral and the color of the dye is also a big plus, because there are some wavelengths for which lasers are expensive or harder to build.
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This technology isn't unusual; such lasers are often laid down between sheets of glass. Gardiner and his team found a way to print the liquid crystal on any surface using an ink jet-type system. The liquid crystals are printed as tiny dots on a wet polymer that covers a substrate. The polymer dries out and in the process aligns the liquid crystal molecules. Since it can work on any surface, the lasers can be flexible rather than rigid as on glass displays. Once laser light is shined on the printed dots, they emit laser light in either one or two directions. If the material they are printed on is opaque the laser light only goes one way, and if it is transparent it is emitted both front and back.
This kind of technology can be used in the display industry, but Grdiner said he sees more immediate applications in sensing and diagnostics. Currently, everal kinds of medical tests involve using a bio-marker that attaches to the molecule one is interested in and hitting it with laser light. Being able to print an array of hundreds of cheap test sites (each with its own combintion of test substances) would speed those processes tremendously.
The research was published in the Journal Soft Matter.
via University of Cambridge
Credit: University of Cambridge