It ' s time for terahertz

28 Scientists have spent the last century or so busily plundering the electromagnetic spectrum, adapting almost every wavelength possible for all manner of applications. We listen to music through radio waves , cook our dinners using microwaves, turn our televisions on with infrared lasers, find forged bank notes with ultraviolet light and identify broken bones with X-rays. Yet there is one region of the electromagnetic spectrum that has until recently remained relatively untouched. To astronomers who detect it from molecules in gas clouds in the farthest reaches of our galaxy, it 's known as submillimetre radiation. To the rest of the physics community, it 's better known by its frequency: terahertz. Sandwiched between microwaves and mid-infrared light, terahertz radiation runs from about 0.3 to lOTHz (where 1 THz = 10 Hz). Its potential is great: this kind of light could transform cancer screening, sniff out explosives and drugs, or communicate huge amounts of wireless data. However, terahertz radiation has been rarely exploited so far because terahertz generators do not come in a onesize-fits-all format. Synchrotrons can produce lots of terahertz radiation, but they are big, centralized facilities. While you can create pulses of terahertz radiation relatively easily by firing near-infrared titanium-sapphire lasers at a semiconductor, this technique of "time-domain spectroscopy" which can probe ceramics, plastics and other materials looking for hairline fractures or structural abnormalities is expensive. It also lacks the power required by o'ther applications. In 2002 a new way of creating terahertz radiation was invented that, researchers hoped, would revolutionize terahertz physics. Known as the terahertz quantum cascade laser (QCL), this device has a bigger power output and a better signal-to-noise ratio than all previous terahertz devices. Hopes for it were high, but progress in developing compact, room-temperature terahertz QCLs proved slower than expected. Several big challenges still remain so what will it take for terahertz QCLs to take the terahertz throne?