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Laser pulses lasting tiny fractions of a second have created superhighways in the air that are potentially capable of transporting megawatts of laser power. The advance should help scientists detect pollution in the atmosphere. It could also enable more exotic applications such as redirecting lightning and building practical laser weapons.

Lost in the hype surrounding President Reagan’s Strategic Defense Initiative and other laser-based weapon systems was the fact that it’s difficult to deliver large amounts of energy through the atmosphere via laser. Air absorbs laser energy, heats up and expands. That low-density air acts like a defocusing lens, causing the beam to spread apart and weaken.

To traverse meters or kilometers through the atmosphere intact, laser beams have to be released in short, intense pulses. But at about 50 quadrillionths of a second in duration, such pulses can’t deliver enough sustained energy to remotely power an aircraft or burn a hole through an incoming intercontinental ballistic missile.

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