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Anti-Laser Cockpit Screen

(Not) Blinded by the Light
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It seems that idiots shining laser pointers at airplanes is a significant problem for pilots these days, to the extent that the FAA is offering a significant reward for information leading to the arrest of any morons who are out there doing it. Apparently some of these lasers are so bright they can cause physical damage to the eyes of pilots—I heard a story this morning about a pilot who needed to have his cornea scraped as a result of such an attack.

Clearly, this needs to stop, or at the very least pilots need to be protected. To the latter end, you could use a video display that covers the cockpit windshield. But if the display were to fail, you'd have to be able to fly on instruments alone, so you'd need to be able to easily remove the display.

The display would thus consist of a retractable screen and an ultra short throw projector mounted above the screen. The screen slides across the windshield and latches in place with an electromagnetic latch. If the projector fails for some reason, the latch is automatically released and the screen retracts. Conversely, if the screen is retracted manually, the projector cuts out so as not to reflect on the windshield glass.

The display is fed from a camera mounted on the nose. At least if the camera is blinded, the pilot's eyes aren't damaged. Additionally, heads-up information can be added to to the display for the convenience of the pilot.

ytk, Feb 13 2014

Laser briefly blinds police helicopter pilots http://articles.gle...ser-glendale-police
“After being struck by the laser, Robertson was taken to a nearby hospital, where doctors scraped his corneas.” [ytk, Feb 13 2014]

Article with video of press conference http://ktla.com/201...against-aircraft-2/
About 15 seconds into the video [ytk, Feb 13 2014]

Localized Glare Control
[xaviergisz, Feb 18 2014]

[link]






       Before anyone brings it up, it turns out that depth perception is relatively unimportant in flying. Most objects that you see are so far away that it doesn't really apply. Simulators don't provide for depth perception and they're perfectly usable, and anyway there's nothing stopping a one-eyed person from becoming a pilot as long as he or she can demonstrate that such a disability doesn't interfere with the ability to fly.
ytk, Feb 13 2014
  

       //Given that laser pointers emit infrared laser light//   

       Uh, no they don't. That's why they're used as laser pointers. An IR laser pointer would only be good if you were lecturing to a bunch of pit-vipers.   

       In theory, you could give the pilots goggles that had filters specific for the fairly narrow bits of the spectra that red or green pointers fall in.   

       Or just get them to close one eye on approaches.   

       The risk of actual eye _damage_ from any common (ie, less than 1W) laser at distances over a few hundred feet is negligible - the beam won't be perfectly collimated, nor aimed at the pilot's pupil with any steadiness. The report of a pilot having to "have his cornea scraped" doesn't make sense.
MaxwellBuchanan, Feb 13 2014
  

       1 and even 2 watt laser pointers (well, handheld diode lasers) are getting more and more common. In the US, they're required to have a lock (the one source I found quickly had a code lock), but that doesn't prevent deliberate misuse. And collimation on the 2W is less than a tenth of a degree.   

       In that range you're talking about at least flash blindness from even momentary exposure up to a km or so.
MechE, Feb 13 2014
  

       //The risk of actual eye _damage_ from any common (ie, less than 1W) laser at distances over a few hundred feet is negligible - the beam won't be perfectly collimated, nor aimed at the pilot's pupil with any steadiness. The report of a pilot having to "have his cornea scraped" doesn't make sense.//   

       Well, that's what this article from 2010 says (link), and I have no particular reason to think it's inaccurate.
ytk, Feb 13 2014
  

       // // laser pointers emit infrared// no they don't // yes they do; they frequency double IR to get the colour then let the leftovers escape to avoid heat buildup.   

       So a coating on the cockpit glass which reflects the exact wavelengths. Assuming such coatings exist. Doesn't sound cheap.
FlyingToaster, Feb 13 2014
  

       Most laser pointers are not frequency doubled. They are usually direct diode lasers. And even if they were, the emission (meaning what actually comes out of the business end) isn't IR.   

       And the cost to coat an aircraft windscreen in a multi-point narrow band blocking filter would be in the thousands of dollars range. Maybe the low 10's, but not much more. This is based on the price of coating significantly smaller lenses, but they scale reasonably linearly. Given the number of different lasers out there, however, blocking all of them will significantly interfere with vision. Finally, finding a coating that will work and not degrade on a polycarbonate windscreen is going to be difficult.
MechE, Feb 13 2014
  

       //narrow band blocking filter// stacking a whole bunch of band pass filter on the windscreen would lead to really sucky transmittance...
bs0u0155, Feb 13 2014
  

       Re. the article, frankly I don't believe it. Seriously, if the guy was dazzled by a laser (i.e., it hit his pupil) which was also powerful enough to burn his cornea, his corneal burns would be the least of his problems - he would have permanent retinal damage.   

       I also don't believe that any laser less than several watts (which is a fairly serious laser, not a laser pointer or even a hacked BluRay laser) is going to burn a cornea at distances of hundreds of feet or more. The beam (which would have to be incredibly well collimated, by the way) is not going to remain fixed at one point on the target for more than milliseconds. Enough time to dazzle; possibly enough time to damage the retina (unlikely, to be honest) but not enough to "burn" a cornea.   

       So, I suspect that the Glendale News (trustworthy though it may be on optomedical matters) has made a mistake in this instance.   

       But, regardless, a regular laser pointer (even including the cheap Chinese ones which are often well over the stated milliwatts of power) is going to dazzle pilots, not cause permanent damage.
MaxwellBuchanan, Feb 13 2014
  

       //So, I suspect that the Glendale News (trustworthy though it may be on optomedical matters) has made a mistake in this instance.//   

       Direct quote from the pilot: “I was immediately taken to the hospital, where what they did was scrape off the top layers of my eyes, which I can assure you is extremely painful.”   

       There's even a video of him making this statement at a recent press conference, which is how the story came to my attention (link #2).   

       I obviously can't vouch for the veracity of his statement (or the medical necessity of the procedure in this instance), but his claim is definitely that he had to have his corneas scraped following a laser attack.
ytk, Feb 13 2014
  

       //stacking a whole bunch of band pass filter on the windscreen would lead to really sucky transmittance//   

       They can block more than one band per filter (the one we use at work has a secondary blocking range to keep out stray light from a distance sensor), but I'm not sure what the upper limit is, and you're talking about like 15 or so bands that need to be blocked.
MechE, Feb 13 2014
  

       //and you're talking about like 15 or so bands that need to be blocked//   

       Personally, I vote we start with The Black Eyed Peas and Tom Petty.
ytk, Feb 13 2014
  

       [ytk] Well, I'm sure he thought they were scraping his corneas. Both of them? And yet the laser that burned both his corneas did no permanent damage to his retina? Nah. Someone somewhere got something wrong. It happens.   

       But that is beside the point. My point was that the sort of lasers that the average moron is likely to have access to are not capable of doing damage to the eye of a pilot several hundred or more feet away. A regular laser pointer is even less capable of doing harm. Dazzling (which can last seconds or minutes), on the other hand, is a serious risk.
MaxwellBuchanan, Feb 13 2014
  

       See my above anno on what's available on the market. You're looking at a 2W beam with a diameter of about 3cm at 1km. Full, direct sunlight is .1 W/cm^2, that beam intensity is .28. You don't think that could present a serious distraction, and possibly real harm if it happened to stay on the eye for any length of time?
MechE, Feb 13 2014
  

       //You don't think that could present a serious distraction, and possibly real harm if it happened to stay on the eye for any length of time?//   

       A serious distraction, and dazzlement (lasting for seconds or minutes afterwards) yes, definitely.   

       Permanent damage - no. You can (though it's not advisable) look at the full sun for seconds; you'll be unable to see much for many seconds (up to a minute, maybe) thereafter, but your eyes will recover just fine, as long as you don't do it dozens or hundreds of times.   

       Your laser delivers three times the power, but natural blink and aversion reflexes mean you won't be exposed for more than about 1/20th of a second.   

       So yes, it will dazzle badly and impair vision for seconds or minutes thereafter, but it won't cause permanent damage.
MaxwellBuchanan, Feb 14 2014
  

       The maximum permissible exposure to laser radiation is apparently 2.5*10^-3 W/cm^2 for a duration of .25 seconds. Given the .28 figure provided by [MechE], the MPE would be exceeded after 1/448 second of exposure. Even a reaction time of 1/20 second would yield an exposure of over 22 times the MPE.   

       I don't honestly know how conservative these safety guidelines are, or how the likelihood of permanent damage scales as you exceed the MPE, but I do know that a laser with more than 5 milliwatts of power is capable of causing permanent eye damage, so I don't see how you can dismiss it as impossible that a laser with an effective power 280mW could do so as well.
ytk, Feb 14 2014
  

       The only simple solution I can think of would be mandate that all laser pointers emit right circularly polarised light. This would be relatively simple since most lasers emit linearly polarised light, so only a quarter-wave retarder would need to be added.   

       All cockpit windscreens would be coated in left circularly polarising filter; any laser light shining at the cockpit would be almost completely attenuated.   

       A similar proposal for headlights and car windscreen was also made (this problem has been mainly addressed with high-beam & low-beam headlights).
xaviergisz, Feb 14 2014
  

       // I don't honestly know how conservative these safety guidelines are,//   

       They are very conservative. Put it another way: they make looking at the sun for 1-2msec out of bounds. Certainly, it's not advisable to look directly at the sun, but if you do (with the naked eye), an exposure of a second (or even many seconds) will not cause permanent damage.
MaxwellBuchanan, Feb 14 2014
  

       I'm not sure how much this modifies the equation, but if a laser dazzlement attack occurred at night, it is likely that the pilot's pupils would be much more dialated than during the day when one might have a chance to look at the sun.   

       Of course pupil dialation wouldn't have any impact on cornea damage, but I agree completely with [Max] that cornea damage from a distant laser without retina damage sounds very unlikely.
scad mientist, Feb 14 2014
  

       I was told of someone who was sent to the cardiac unit after his finger was badly burned by a car battery shorting through his ring - on the grounds that the incident involved electricity.   

       Perhaps the doctors made a similar over-generalisation here. Exposure of the eyes to welding light damages the corneas; lasers are also light; therefore we need to treat the patient for corneal burns.
spidermother, Feb 16 2014
  

       I would suggest using something akin to the screen on an auto-darkening welding helmet - which would detect the bright light and very rapidly turn opaque.   

       At the same time, the system could switch over to a backup display by clever implementation of a projector which would switch on and display an image-enhanced, heavily filtered or even just infrared display from forwards pointing cameras would work well. The transition could be very rapid and the backup image would be nearly instantaneously put up.
Custardguts, Feb 18 2014
  

       Why can a simulated image not be projected on the windshield itself with any high intensity light source filtered out?
The dang things practically fly themselves now anyway, and auto-darkening could possibly be used to cause crashes if a pilot were landing using hand-eye coordination alone.
  

       Mount your own laser on the airplane and shoot it in the direction of the incoming laser to destructively interfere with it.
Cuit_au_Four, Feb 18 2014
  
      
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