For years, the U.S. military has explored a new kind of firepower that is instantaneous, precise and virtually inexhaustible: beams of electromagnetic energy. Directed-energy" pulses can be throttled up or down depending on the situation, much like the phasers on "Star Trek" could be set to kill or merely stun. Such weapons are now nearing fruition. The hallmark of all directed-energy weapons is that the target -- whether a human or a mechanical object -- has no chance to avoid the shot because it moves at the speed of light. At some frequencies, it can penetrate walls. "When you're dealing with people whose full intent is to die, you can't give people a choice of whether to comply," said George Gibbs, a systems engineer for the Marine Expeditionary Rifle Squad Program who oversees directed-energy projects. "What I'm looking for is a way to shoot everybody, and they're all OK." Among the simplest forms are inexpensive, handheld lasers that fill people's field of vision, inducing a temporary blindness to ensure they stop at a checkpoint, for example. Some of these already are used in Iraq. A separate branch of directed-energy research involves bigger, badder beams: lasers that could obliterate targets tens of miles away from ships or planes. Such a strike would be so surgical that, as some designers put it at a recent conference here, the military could plausibly deny responsibility. The directed-energy component in the project is the Active Denial System, developed by Air Force researchers and built by Raytheon Co. It produces a millimeter-wavelength burst of energy that penetrates 1/64 of an inch into a person's skin, agitating water molecules to produce heat. The sensation is certain to get people to halt whatever they are doing.

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