Just as x-ray technology came along in the 1890s—allowing doctors to peer beneath flesh to see bones and organs—another promising imaging technology is now emerging from an underused chunk of the electromagnetic spectrum: the terahertz frequencies. These so-called t-rays can, like x-rays, see through most materials. But t-rays are believed to be less harmful than x-rays. And different compounds respond to terahertz radiation differently, meaning a terahertz-based imaging system can discern a hidden object’s chemical composition.

Thanks to this power, “terahertz imaging is getting hotter and hotter,” says Xi-Cheng Zhang, a terahertz pioneer at Rensselaer Polytechnic Institute. Potential applications range from detecting tumors to finding plastic explosives. And since t-rays penetrate paper and clothing, a terahertz camera could detect hidden weapons.

Terahertz frequencies are tough to produce and detect. They’re higher than microwaves but lower than infrared light.
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