At the airport, the next generation of body scanners may rely on terahertz radiation, or T-rays. Unlike X-rays, T-rays are not energetic enough to strip electrons from atoms, making them safer for humans. They are also exceptionally sensitive to chemical structure, easily able to distinguish over-the-counter drugs from illegal substances. Before T-ray cameras and scanners can become a reality, however, researchers need to learn to control the radiation more precisely. Electrical engineer Qing Hu at MIT demonstrated a method to tune a terahertz laser by changing the diameter of the cavity emitting the rays, allowing him to finesse the beam to specific frequencies. And researchers at Texas A&M and Rice University are learning to control the rays by adjusting the temperature of a semiconductor film they pass through.