Claire Gmachl

Her lasers could serve as early-warning systems for terrorism.

When Claire Gmachl worked at Bell Labs, she had a parlor trick that never failed to delight visitors. She would place a lens a few inches from a laser and clamp a matchstick six inches in front of the lens. Then she'd use the lens to focus the laser's invisible infrared beam onto the matchtip, and voil! She could light a match without touching it. You might think a scientist would be glad to have an entertaining way to show off the power of her devices. But to tell the truth, Gmachl found the exercise a bit "dorky." She has little patience for distractions.

Gmachl, 37, has plenty to focus her laserlike intensity on these days. Once perfected, her tiny, ingenious devices--quantum-cascade lasers--could be used to detect biological and chemical weapons or to sniff airports for explosives. Bell Labs investigators invented quantum-cascade lasers before Gmachl arrived in 1996 from her native Austria, but theirs had a big shortcoming--one she figured out how to overcome.

Every gas molecule absorbs unique frequencies of light, creating a distinctive chemical fingerprint. Lasers are the classic tool for detecting these fingerprints, but until recently they consisted of bulky gas-powered ones or unstable solid-state ones. Quantum-cascade lasers, in contrast, are small, rugged semiconductor pastries whose layers form an
"energy staircase"--a series of progressively lower energy states. An excited electron cascades from layer to layer, shedding energy in the form of a photon with each jump. The beauty is that simply changing the thickness of the layers changes the laser's frequency. Initially, though, the Bell Labs quantum-cascade lasers emitted a messy, uneven spectrum of light, making them incapable of identifying the telltale absorption frequencies of various chemicals. Gmachl's feat was to etch a grating onto the laser that precisely amplifies one frequency and filters out the rest. She later designed lasers that emit multiple frequencies, making it possible for a single instrument to detect many different chemicals. Shining one of Gmachl's lasers across a highway to a sensor on the other side would create a detection system for noxious car emissions; installed in an airport walkway, such a laser could sense trace amounts of explosives. Gmachl, now at Princeton, is trying to make her lasers, which function best at -200