For decades, scientists have been slowly working on a laser that never runs out of shots -- and can be "tuned" to blast through the air, at just the right wavelength. For most of that time, all they could get was a laser at lightbulb-strength. But in 2004, researchers at the Thomas Jefferson National Accelerator Facility finally managed to assemble a "Free Electron Laser," or FEL, that could generate 10,000 watts of power. The Navy has started an effort to design and build a new FEL, 10 times as strong. That would bring the laser up to 100 kilowatts -- what's considered the minimum threshold for weapons-grade. But it would also be just a stepping stone, on the way to an energy weapon as powerful as any produced.

If ray gun researchers can get the thing to work, that is. The Navy is interested in the FEL because most other lasers lose strength as they move through — and get absorbed by — the atmosphere. That's especially in moist environments; above the sea, for instance. But the FEL can pick particular slices of the spectrum where the absorption won't be nearly as bad. In other words on a cloudy day shooting a spy plane or an enemy missile was not possible by a laser until now.

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