快猫短视频

IT BEGINS without warning. You are driving fast on the highway and your vision starts to blur. As vehicles around you become hazy and the road ahead fades, you lose control. Even if you survive the impending crash, no one may ever find the cause, because you have been targeted by a weapon that leaves no trace.

Such a device already exists. Tagged by its developers as non-lethal, it is a laser designed for use by security services or on the battlefield. It sends out an invisible beam that temporarily blurs vision, apparently without damaging the eye. The hope is that it could be used to temporarily blind potential snipers or disable terrorists before they act.

Visible lasers have been aimed at the police during riots and public protests (Image: Todd Darling/Polaris/Getty)

But the story is not quite so clear-cut. Would such a laser be less dangerous than conventional alternatives, such as laser dazzlers or tasers? After all, with a driver or pilot in the firing line, it could cause fatalities. What鈥檚 more, there would be no evidence of the cause. Aviation authorities are already trying to prevent people from shining powerful laser pointers at aircraft, fearing they will blind pilots. Such pointers produce visible light, so at least there is a chance of deterring or catching the culprits. But it is a different story with this weapon. In the wrong hands, it would cause chaos.

Lasers concentrate energy into intense light beams, so it is hardly surprising that people have tried to turn them into weapons. In the 1980s, for example, the UK Royal Navy developed a system to blind attacking pilots, and the US created lasers to defend aircraft, helicopters and vehicles. Laser weapons capable of blinding people were in 1996, after a successful campaign.

Yet lasers that cause temporary vision loss are still permitted. Laser dazzlers or 鈥渙cular disrupters鈥� used to send signals or as dazzlers are widely used. The , for example, is a flashlight-sized device that was fielded by the US military in Iraq to signal to drivers as they approached checkpoints. And the US police and coastguard service received the go-ahead to use laser dazzlers in 2012.

Although designed to be safe, these devices can still damage eyes, particularly when used at close range. To help prevent this, dazzlers have a minimum safe distance at which they should be operated 鈥� and some even switch off automatically when a target is too close. Despite this, . It is not clear how many civilians have been affected.

So if lasers are going to be used in these ways, there鈥檚 a need to make improvements. Researchers have tested strobing lights, and combinations of light and sound that can disorientate, even at low light intensities. Then in 2009, researchers from defence technology company Northrop Grumman and the Air Force Research Laboratory at Brooks City Base in Texas came across a promising lead: they noted that mammal eyes are particularly resistant to damage by infrared laser light at a wavelength of 1320 nanometres. In tests it took at least at this wavelength to damage the retina than at shorter wavelengths.

Further studies revealed why: although our eyes can鈥檛 detect light at around 1300 nanometres, the infrared is absorbed by the structures of the eye 鈥� the lens, cornea and the fluid inside the eyeball 鈥� and they heat up. This changes the eye鈥檚 refractive index, altering the way light travels through it. The effect, known as thermal lensing, prevents the eye focusing the light onto the retina, so there is no tight pinpoint of light to cause damage.

Thermal lensing seems to open the door to all kinds of remarkable effects. In tests with low-power infrared beams, the air force team, working with researchers at the University of Texas at Austin, found they could blur the eyesight of volunteers, making it appear that they were gazing through a heat haze. In another , published in 2014, the team reported reducing the eye鈥檚 ability to focus by 2 dioptres, equivalent to inducing moderate short-sightedness. With more powerful beams, they found they could entirely block out parts of their volunteers鈥� vision. All these effects disappeared as soon as the laser was turned off and didn鈥檛 heat the eye enough to cause damage, says Benjamin Rockwell, one of the team at the Air Force Research Lab. With much the same range as a conventional laser, it seems to offer a less-dangerous alternative to visible-light dazzlers, he says: 鈥渁 unique way to temporarily challenge someone鈥檚 vision鈥�.

Any device that manipulates eyesight could make a powerful weapon. It could certainly stop a sniper, or disable a driver approaching a checkpoint. But there are still possible problems, says J眉rgen Altmann, a physicist at the Technical University of Dortmund in Germany. 鈥淲henever one manipulates the human eye, there are obvious safety issues,鈥� he says. We don鈥檛 fully understand thermal lensing yet, he says, so more research is needed on the effect and its implications. There is a big difference between controlled tests in a lab and the much broader beams used during actual operations, he says.

Stephen Coleman from the University of New South Wales in Canberra, Australia, who studies military ethics, warns that using any kind of invisible light is inherently more dangerous: 鈥淲ith visible dazzlers, exposure is limited because people look away.鈥� But with an infrared laser, there鈥檚 no such limitation 鈥� people might blink more, but not turn away. Those using such devices may also ignore limits because they can鈥檛 see their targets react. 鈥淪afety limits might be exceeded because there鈥檚 no visible effect for the user: 鈥業鈥檝e been using it for 5 seconds and nothing is happening, I鈥檒l keep using it鈥�,鈥� says Coleman. And anyway, he adds, the device is simply not suitable for police use. 鈥淲eapons like pepper spray, tasers, and even firearms, disable suspects so they can be taken into custody. This blurs vision. The range of circumstances in which it could be used is very limited.鈥�

Combining the infrared beam with a visible laser could get around some of these problems, Rockwell believes. This pairing could disrupt vision more effectively in daylight, at lower energy levels, he suggests. 鈥淭here may be an optimal configuration which allows higher exposures before a dangerous level is reached.鈥�

On the other hand, this combination could also increase the potential for blinding in some people, Rockwell and his colleagues say. The eyes of people who are long- or short-sighted are unable to focus light on the retina, and thermal lensing might provide exactly the change their eyes need for perfect focusing. The device could temporarily improve their vision and so cause serious eye damage.

Close to market

It might be some time before the military turns infrared lasers into practical weapons, but others may not take so long. Last year, security equipment provider Shield Defense Systems of Reno, Nevada, announced a called Z-RO. The company鈥檚 website claims it blocks vision for 10 to 15 minutes, but will not damage the retina or cornea 鈥渁s these are not targeted to achieve the visual obfuscation effect鈥�. Although the company won鈥檛 discuss this technology, its details appear to match the US air force鈥檚 thermal lensing laser. Shield claims Z-RO is in the manufacturing stage, and should be available soon.

Whatever happens, lasers operating at a wavelength of 1320 nanometres are already used in research labs, for medical treatments such as scar removal and in optical communications systems. Shrinking these lasers to weapon-size portability remains a challenge, but laser technology is advancing rapidly, so this may not take long. And that鈥檚 when the real problems could begin.

Some of the challenges arising from small, portable lasers are already evident. According to the US Federal Aviation Authority, in the US alone there are 11 incidents every day in which pilots are targeted with small but powerful laser pointers (see chart). This has caused eye injuries, but no crashes so far. Bus, truck and train drivers have also been targeted. Some incidents have led to accidents.FIG-mg30110801.jpg

Authorities have a chance of tracing people who use visible lasers. That would be much more difficult if they were wielding a thermal laser. 鈥淭here would be much potential for misuse by criminals and irresponsible people, against car drivers, pilots or for robbery,鈥� says Altmann. Even the victim might be unaware of what was happening. 鈥淥nly a small percentage of those exposed have reported any sensation of heating,鈥� says Rockwell. 鈥淓xcept for the visual effect, most are unaware of the exposure.鈥�

It鈥檚 a sobering thought. The truth is, if there鈥檚 one thing worse than knowing you鈥檙e the target, it鈥檚 not knowing.

This article appeared in print under the headline 鈥淏linded by the heat鈥�