Adv. Mater. http://dx.doi.org/10.1002/adma.201303122 (2013)

Credit: © 2013 WILEY

Random lasers have the beneficial properties of a high temporal coherence and a low spatial coherence, making them ideal light sources for imaging with a high photon radiance without the nuisance of coherent artefacts. To date, electrically pumped random lasers have only been realized in ZnO heterostructures; extension to the mid-infrared regime has proved challenging because of the lack of a suitable scattering gain medium and the high optical losses in this regime. Now, Hou Kun Liang and colleagues from Singapore claim to have made the first electrically pumped mid-infrared random lasers. They operate at a wavelength of 10 μm. The researchers fabricated the lasers by etching circular, 10-μm-deep air holes in computer-generated random patterns onto quantum cascade laser heterostructures, which offer high gain in the mid-infrared regime and are amenable to electrical pumping. When such a laser with a sufficiently high density of air holes was electrically excited, the team observed the rise of random lasing peaks caused by multiple scattering and interference clustered closely around the gain peak of the material. The laser's operation threshold was found to decrease with increasing scattering strength and fill factor of the air holes, which is typical for random lasing.