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UV Lasers Stop People in Their Tracks

Photonics Spectra
Jan 1999
Aaron J. Hand

Mork from Ork could freeze people in midaction with a simple point of his alien finger -- diminishing them to dancing, talking, running statues. Now researchers at HSV Technologies Inc. have come up with a device that could put this power into the hands of police, enabling them to freeze a suspect on the run.
Unlike the Taser, which works by shooting the target with two small darts connected to the gun by thin wires, the "tetanizer" does not have to make physical contact with the target, enabling use at greater distances and without causing pain. It uses ultraviolet laser beams to tetanize people or animals, temporarily immobilizing them from as far as 100 m away.
The UV radiation creates an ionized path in the air along which an electrical current runs to the target. The current imitates the neuroelectric impulses that control skeletal muscles, tetanizing muscle tissue -- or sustaining its contraction --without pain. The device uses a current that is too weak to affect smooth muscles such as the heart and diaphragm. Also, the laser beams are technically eye-safe because it would take several minutes to damage the retina at the UV wavelength.
Engineers do not yet have a working prototype, noted Jan Eric Herr, vice president at HSV Technologies and inventor of the tetanizing device, because they have not yet found the appropriate laser. The researchers have successfully tested the device using a Lumonics Hyper-X 400 excimer laser at the University of California at San Diego. About the size of a small refrigerator, the 193-nm ArF excimer certainly does not resemble the handheld weapon they are aiming for, however. Developers are now looking at a new 193-nm excimer laser. Lambda Physik's OPTex is about the size of a carry-on suitcase. "Nonetheless, it's nowhere near as small as we need it to be," Herr said.
Herr still thinks the chances of eventually being able to construct a handheld tetanizing weapon are very good. The laser it uses, however, will probably not be an excimer, which has sufficient power but presents a problem in that it's pulsed. Lambda Physik's laser offers a pulse rate of up to 200 Hz. Although this is an improvement over the 40-Hz rate of Lumonics' laser, it still may not be fast enough to compensate for the very fast rate at which electrons recombine with the air molecules from which they were dislodged, Herr said.
On the other hand, continuous-wave lasers tend to be much weaker. "We need a continuous-beam laser with the same power level as present-day excimers," Herr said. "And I know work is being done on them."
A different version -- one that disables cars -- could probably be made available in about two years, Herr said, because it would not face the same obstacles as a handheld version. "The engine-disabling variation would not require a significantly smaller laser than is now available because it could be carried in a police car rather than by hand," he said. "The current would have to be a little heavier, but not so refined."

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