Fine-tuned
For more than 30 years, scientists have been trying to harness the power of terahertz radiation. Tucked between microwaves and infrared rays on the electromagnetic spectrum, terahertz rays can penetrate clothing, plastic, and human tissue, but they’re thought to be safer than x-rays. Since they’re absorbed to different degrees by different molecules, they can also tell chemicals apart: a terahertz scanner at an airport checkpoint, for example, could determine whether a vial in a closed suitcase contained aspirin, methamphetamines or an explosive.But practical ways to generate terahertz rays have been hard to find. Traditional gas lasers can operate in the right frequency band, but they’re big, expensive, and power-hungry. Semiconductor lasers — the kind you find in a DVD player — are small and cheap, but they’re hard to nudge out of a limited spectral range: consider how long it took to get from the infrared lasers of the first...