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FBI Investigating Laser Beams Pointed at Aircraft
sakshale writes "In an earlier discussion about Laser Pistols, many people argued about the concept of using them to target pilots of airliners. Apparently the FBI is investigating incidents in Cleveland and Colorado Springs. They issued a warning on December 14th."
Given some time, and--right or wrong--somebody will attempt to pile on the regulations and we can forget about buying green lasers from ThinkGeek or anyplace else.
Sigs cause cancer.
You can easily find computer operated 60w lasers. And yes its beam is 5 inches wide.
That would hurt.
They didn't shine it at a plane directly overhead, the pointed it at a plane a few miles away. At that distance, even at an altitude of a few thousand feet, the pilots still have a clear line of site to the ground. The could be hit much closer if the incoming beam was slighly angled to come in from the front side and not straight ahead over the center of the nose.
Green appears the brightest on the human spectrum. Most of these small lasers are DPSS (Diode pumped solid state). If the beam is coherent it is *INDEED* a danger, and nothing scares me more than the thought of hoodlums running around with 600mw "laser pointers".
Lasers for display are regulated by the Center for Disease and Radiological Health. Your not supposed to direct a laser above 5mw up into the sky.
At a long distance, the beam definitly becomes incoherent. Gas lasers are considered better than solid state in regards to beam colimation, and without optics my 2.5' long argon tube beam ends up 1' or more wide at a distance of only 1000 feet or so.
Targeting, no... Someone might manage to cross the planes path, but in order to track a plane I'd iamgine you would need to build a box filled with dirt sitting on innertubes to isolate vibration, then come up with a servo mechanism. I don't think 16 bit DACs would give enough accuracy with glavos.
Weapons targeting systems do not use visible lasers AFAIK. It would be a giveaway if there was a bright green dot on the target and a green line tracing back to the source.
Also, laser light is different then searchlights because the light is polarized. So you can see the beam better from one way versus the other.
Southeastern Virginia REPRESENT!
One night I was on a CAP SAR flight and we were targeted by such a laser. They can be very bright when your eyes are accustomed to the dark! When we tried to locate the source and got closer, it stopped. It was coming from a residential area. I had spots in my vision like someone took flash photos and I looked into the strobe.
One note; there was mention in the news of a quote from an FBI agent who said it had to be a sophisticated laser to track a plane for severla seconds at 8500 feet. I disagree. I believe with a braced or tripod mounted unit in combination with the beam divergence holding on target for a few seconds is easy.
Ever look at a plane several miles away that is coming straight or almost straight in your direction? Sometimes it seems like they aren't moving at all. The number of arc seconds they will move in 10 seconds time relative to you is very small. I don't think a gyroscope/mechanical tracker would be necessary.
IAAP (I am a physicist). I do not work with lasers, but have taken a graduate level course in non-linear optics that primarily focused on lasers.
It is quite possible to damage a pilot's eyes at a range of a few miles, using only commercial laser systems. If done by competent individuals, it would probably involve a pulsed infrared laser (harder to detect, and the eye is more susceptible to near IR than to visible). A Nd:YAG laser (1064 nm) would be ideal.
Since a pulsed laser is used, there's no need for tracking the plane. A single 10-nanosecond pulse would be sufficient. At 10 - 20 pulses per second, you could just scan the sky in the area of the plane.
After reading the story, I did some rough calculations. For the above-mentioned laser, the laser beam would do damage (although likely not sufficient to totally blind the pilot) at ranges of up to two miles, and the beam would have a spot size several meters in diameter at that range. Obviously, with additional optics, range and spot size could be changed.
It seems to me that the laser could simply be mounted to a scope on a tripod (after some careful alignment), and that targetting by hand would work at least some of the time.
All this aside, I don't think the recent cases are anything to be worried about. More likely it's just a nutbar with a relatively weak visible laser (I assume the laser was in the visible range because the pilots reported it, and I doubt commercial planes are equipped to detect IR lasers). If it was someone serious, they'd be using IR lasers, and we wouldn't know until pilots started getting eye damage.
That said, the overall risk of plane crashes from this form of attack is low. If the airport and immediate area are kept secure (and they should be if only to guard against Stinger-style missile attacks), it's very unlikely someone with a commercial laser could get close enough to completely blind a pilot. Military or custom-built research lasers could blind from greater distances, but such systems are very finicky, and I can't see terrorists pulling that off.
Finally, I'd like to address a few points other people have brought up. If the polarization and angle of the beam are chosen correctly, virtually none will be reflected off the plane's window, and all will be transmitted (see Brewster's Angle). For modest laser powers, the damage to the retina will be localized to where the laser beam is imaged, leaving much of the pilot's vision intact. Bad for the pilot, but he could probably still land. For more intense beams, other damage mechanisms come into play (apparently for severe cases there is an actual popping sound perceived by the victim as the laser pulse creates a small shock wave inside the eye), and more of the victim's vision could be damaged.
Protective goggles aren't really an option, as they only protect against one wavelength. Attackers could then switch to a different type of laser (Ti:saph?). Combining goggles leads to virtually no light getting through.
References
Journal of Biomedical Optics 4(3), 337-344 (July 1999).
Big Sky Laser CFR-800 spec sheet