RESEARCHERS at Arizona State University have proven that semiconductor lasers can emit the full visible colour spectrum, using a novel nanosheet.
Light from a typical laser contains exactly one colour, a specific wavelength within the electromagnetic spectrum. But researchers have been looking into creating “white lasers”, which provide a complete mixture of all the wavelengths of the visible spectrum.
The researchers created the nanosheet, a thin layer of semiconductor, with three parallel segments. Each segment supports laser action in one of the three elementary colours: red, green, and blue. By collecting all three fields, the researchers say a true white colour laser beam is created.
The main reason for creating white lasers is to use it for illumination. Lasers could become a mainstream light source, replacing or acting as an alternative to LEDs. They are brighter, more efficient, and can provide more accurate and vivid colours for displays, like computer screens and televisions.
True white lasers could also allow light-based wireless communications, where visible light is used for both illumination and communication. Currently, LED-based light communication is under development, but white laser based communication could be 10 to 100 times faster than LED-based communications.
In 2011, Sandia National Labs used four separate large lasers to produce high quality white light. However, the laser could not be used for room lighting or in displays. Researchers needed to find a way for a single piece of semiconductor material to emit laser light in all colours or in white – an achievement the Arizona State University scientists say they have completed.
The main challenge for the researchers was lattice mismatch, where the lattice constant was too different for the various materials required. This was primarily because it was not possible to grow different semiconductor crystals together in high enough quality, using traditional techniques.
The researchers turned to nanotechnology, figuring 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.
The next step will be to create white lasers that can be driven by a battery.
