The United States Navy's laser weapon. It can be used to ablate, ignite or otherwise damage an air or sea target.

When the Navy announced last month that it was deploying a shipboard laser weapon in the Persian Gulf, it seemed that the future of warfare had arrived, in which the enemy could be blasted from the sky by a beam of light.

The beam of light part is basically accurate — that’s what a laser produces, although in this case the light is not in the visible part of the spectrum. But the Navy weapon does not blast anything; instead, it heats its target, bombarding it with light particles until it ablates, ignites or otherwise is damaged. It is death by a bazillion photons.

Peter A. Morrison, manager of the Navy program, said the weapon’s lasers use a crystal that has been doped with a rare-earth element. Light-emitting diodes are used to “pump” the crystal — transferring energy into it and stimulating the emission of photons, which all have the same energy and exit the crystal from one end in a tight beam. Multiple lasers are used, and the beams can be focused so they overlap on the target, concentrating the photons on a small area.

Since the weapon relies on gradual heating, accurate tracking of the target is crucial. The Navy system first relies on radar to supply a general range and heading, Mr. Morrison said, and then hands the tracking off to an optical system, lighting up the target with lower-energy laser pulses if necessary. Once the target is identified as a threat, the LEDs are switched on, activating the higher-power beams. Then it’s just a matter of time until the photons do their thing.

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