Jul 8, 2009 8:59 AM

Military Looks to Stop Drivers With Laser Blasts

Laser dazzlers — or “optical distraction devices,” as the military prefers to call them — have proven invaluable in Iraq as a way of warning drivers to stop at checkpoints. (A flash of bright light does tend to give people pause.) But as Danger Room reported, several U.S. troops have suffered serious eye injuries from […]

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Laser dazzlers -- or "optical distraction devices," as the military prefers to call them -- have proven invaluable in Iraq as a way of warning drivers to stop at checkpoints. (A flash of bright light does tend to give people pause.) But as Danger Room reported, several U.S. troops have suffered serious eye injuriesfrom laser "friendly fire" incidents. So the U.S. military's Joint Nonlethal Weapons Directorate is developing a new type of laser which aims to be both safer and more effective than existing dazzlers, I report in New Scientist. Whether it will work is still an open question.

Rather than a continuous beam, the Laser Windshield Obscuration project works by firing a short laser pulse, which is absorbed by the vehicle windscreen. That produces a brilliant white 're-radiation' flash (see photo, right), leading to cracking or hazing of the glass (photo, left).

Originally, the objective was to cause the maximum amount of the damage to the windscreen, making it impossible to see through. As the photograph shows, the laser is certainly capable of it. The concept is similar to the lens-destroying "laser crazer" project, proposed for knocking out cameras and other sensors. However, researchers found that the bright flash was enough to cause "optical incapacitation" or dazzling of the driver. Work is now concentrating on changing the output to produce a brilliant flash with minimum damage; ideally, the windscreen would not need to be repaired or replaced.

The laser flash should give a clear and unambiguous signal to stop. If the driver does not stop in spite of the warning, they may be assumed to be a suicide bomber and more lethal means will be used. (And a dazzled suicide bomber should be slightly less dangerous).

Existing laser dazzlers have the double problem of limited effectiveness in daylight and the potential to cause eye damage at short range. The JNLWD say that the Windshield Obscuration Laser will be equally effective in all lighting conditions. And, since the brilliant flash is generated at the windscreen, it should have the same effect at five meters or five hundred.

The concept is highly reminiscent of the more powerful Pulsed Energy Projectile. This fires a short laser pulse, which vaporizes a tiny spot on the surface of the target, producing a "flash bang" plasma explosion. It was intended as a non-lethal weapon, but after years of development was determined to be unsuitable for use against people and was taken up by an anti-drone program.

Laser Windshield Obscuration sounds fine if the laser pulse strikes a windshield. But what happens if someone gets it in the eye? The military knows a lot about this subject and have been exploring the effects of short laser pulses on eyeballs since 1998 with the specific aim of making sure their lasers are safe. "It is possible for the laser to generate the desired effects to be eye-safe," says Scott Griffiths of the JNLWD's Vehicle-Stopping Technology Office. "A human effects risk assessment is planned to characterize the potential hazards to humans."

Curiously enough, the effects may not be that bad. Unlike other lasers, which will go right through the eve and damage the retina, this laser will be stopped at the outer layers.

"Shorter wavelengths are not absorbed into the eye but can damage the surface - arc eye or snowblindness,” Bruce Allan, Consultant Ophthalmic Surgeon at Moorfields Eye Hospital in London tells Danger Room. “The corneal skin layer damaged in arc eye regenerates quickly, and although the condition is very painful, there should be no lasting damage."

So rather than causing retinal damage and blindness, the new laser should only cause temporary damage if it strikes someone in the eye. Of course this should not happen anyway; but, as we have seen with existing dazzlers, operators do not always follow the rules and accidents happen.

It's not yet known whether the Laser Windshield Obscuration system will be a handheld unit or a large vehicle-mounted system. The conceptual design will be completed by the end of 2009, and a prototype demonstrator will be built in 2010. Meanwhile the JNLWD are exploring other vehicle-stopping concepts, including a microwave device to stop engines.

Picture: Joint Nonlethal Weapons Directorate