An advance in laser technology combines the broad spectral features of a random laser with the spectral stability and high directionality of a traditional laser. Such an advance could enable greater use of random lasers in applications where a broad spectrum illumination source would be of benefit. Researchers at the University of New Mexico, in collaboration with researchers at Clemson University and the University of California San Diego, demonstrated a directional random laser in a disordered glass optical fiber. The laser operates in the Anderson localization regime. To direct the laser, researchers fabricated a glass Anderson localizing optical fiber made of "satin glass," an extremely porous glass that, when pulled into long rods, forms microscopic air channels in each fiber. The research team fabricated a new type of optical fiber that is capable of controlling these random lasers. Courtesy of University of New Mexico. “The glass that we’re using for these fiber optics is actually material that we would typically throw away because it is very porous,” said researcher Behnam Abaie. “But, it’s those holes in the glass that are actually creating the channels that control the laser.” Disorder-induced localized states form channels across the transverse dimension of the Anderson localizing optical fiber made with glass (g-ALOF), which direct the output laser beam and stabilize its spectrum. Upon excitation of one of these channels by a narrow input pump, the device starts lasing. The strong transverse disorder and longitudinal invariance result in isolated lasing modes, traveling back and forth in a Fabry-Perot cavity formed by the air-fiber interfaces. Experiments showed that if a localized input pump was scanned across the disordered fiber input facet, the output laser signal would follow the transverse position of the pump. A point-to-point correspondence between the transverse position of pump and output laser was achieved. Further, a uniformly distributed pump across the input facet of the disordered fiber was shown to generate a laser signal with very low spatial coherence. This could be of practical importance in many optical platforms including image transport with fiber bundles. Researchers attributed the stability of the laser spectrum to the strong mode confinement provided by the localized states in g-ALOF. (l) to (r): University of New Mexico Ph.D. student Behnam Abaie and Associate Professor Arash Mafi observe computer measurements being taken during a test of their device. Courtesy of University of New Mexico. “Our device has all the great qualities of a random laser, plus spectral stability — and it is highly directional,” said professor Arash Mafi. Although a single random laser can produce a beam of light containing multiple spectra, random lasing so far has not been useful for most practical applications because it is difficult to reliably control. Previous demonstrations of random lasers have found limited applications because of their multi-directionality and chaotic fluctuations in the laser emission. Moving forward, Mafi says the researchers hope to broaden the spectrum of this new device and make it more efficient, creating a broad spectrum illumination source that could be utilized around the world. “Our success in being able to control these random lasers addresses decade-old issues that have prevented these lasers from becoming mainstream devices,” he said. “It's a very exciting contribution.” The research was published in Light Science & Applications (doi: 10.1038/lsa.2017.41).