A semiconductor laser chip measuring approximately 3mm x 1.5mm contains 10 lasers. A scanning electron microscopy magnification (right) shows one of the laser cavities. Periodic slits in the thin-film top metal layer provide the distributed feedback in the cavity. Credit: Sushil Kumar
Lasers have become indispensable to modern life since they were invented more than fifty years ago. The ability to generate and amplify light waves into a coherent, monochromatic and well-focused beam has yielded applications too numerous to count: laser scanners, laser printers, laser surgery, laser-based data storage, ultrafast data communications via laser light, and the list goes on.
Lasers are found in all shapes, sizes and colors. They can be made of gases (gas lasers) or based on solid materials (solid-state lasers). They can emit light of different colors (or wavelengths or frequencies), from X-rays (short wavelengths) to visible to far-infrared (long wavelengths). They can be as big as a building (free-electron lasers) or as small as a laser pointer (semiconductor diode lasers).
Terahertz QCLs, however, also emit highly divergent beams, which poses an obstacle to commercialization.
In this illustration of a terahertz plasmonic laser, the laser cavity is enclosed between two metal films (with periodic slits on the top film). The colors represent coherent SPP light waves. One wave is confined inside the 10-micron-thick cavity. The other, with a large spatial extent, is located on top of the cavity. Credit: Sushil Kumar
"A periodic structure can also enhance the quality of the laser beam by channeling light intensely into a tight spot. Such narrow beam lasers can deliver light energy to a location where it is needed most. They can shine for long distances, and are easier to manipulate and re-direct at a desired location using small optical components."