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Dave W.
Info Junkie
USA
26020 Posts |
 Posted - 01/03/2005 : 19:29:24 [Permalink]
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quote:
Originally posted by Siberia
But aren't lasers invisible, unless they're in a foggy background? Or are we speaking about different things? Or am I just mis/uninformed? [confused]
If you're looking right at them, they're plenty visible. If you're off to one side of the beam, you'll see less of its light, but not none of it because the beam spreads out just bouncing off air molecules (and more because of dust or moisture or other little tiny stuff).quote:
Either case, I don't doubt they can cause potential damage in long ranges... what I doubt it's that someone could actually pinpoint a person's eye inside a plane's cockpit, and even so, that it would crash a commercial plane. I understand what HH means, but my mind's not connecting it with lasers, only a very strong light [blink]
A powerful enough beam can be extremely bright even at long distances, meaning "pinpoint" accuracy isn't required. But for that high power, we'd be talking military and/or university lasers, and not something at all portable.
When I first heard of the lasers-in-the-cockpit deal, it was guessed that someone was farting around with one up in the mountains near one end of a runway (thus allowing a near-horizontal "shot" with low lateral speeds). But even then, I can't imagine a major airport with mountains less than five miles or so from the end of the runway(s). And five miles would be a lot to ask of any laser drivable up a mountain without bringing a lot of attention to yourself. |
- Dave W. (Private Msg, EMail)
Evidently, I rock!
Why not question something for a change?
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Ricky
SFN Die Hard
USA
4907 Posts |
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ktesibios
SFN Regular
USA
505 Posts |
Posted - 01/03/2005 : 23:01:04 [Permalink]
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quote:
Originally posted by Siberia
But aren't lasers invisible, unless they're in a foggy background? Or are we speaking about different things? Or am I just mis/uninformed? [confused]
Even if the laser emits light at a visible wavelngth, the beam will be invisible unless there's dust or haze in the air to scatter some light in your direction- assuming, of course, that you're not actually in the beam.
At the Floyd show I mentioned, the lighting people were working some smoke machines very hard to try to produce enough haziness to make the beams visible, but there was a breeze blowing much of it away. The irregular distribution of smoke did produce a neat looking sort of string of beads effect, and you could look up and see where the beams were hitting the clouds. |
"The Republican agenda is to turn the United States into a third-world shithole." -P.Z.Myers |
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Starman
SFN Regular
Sweden
1613 Posts |
Posted - 01/04/2005 : 01:50:37 [Permalink]
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It was several years since I played with lasers but here is my take.
Terrorists please do not read beyond this point!
If you want to use a laser to blind someone you should not use green light. Infra-red is much better as the victims eyelids offers very little protection in those frequencies.
Lasers with enough power, should not be to hard to get hold of. CO2 lasers (between 9 and 11µm) are available for cutting and drilling and could probably be available with enough power in car portable models.
If the laser beam is aimed into the cockpit, light will scatter when the beam hits something (windshield, instruments etc.).
This light will be collected by the eye and as it is monochrome, it has much power in a small frequency band, and the energy will be focused (by the eye) in small points on the retina and in the vitreous chamber where serious and most likely permanent damage will be done.
You don't have to focus your beam much(which can only be done to a limit as the beam will react with the air molecules) or hit the victims eyes to have an effect.
When you play(well work) with a laser you wear protective goggles all the time. Not because you might accidentally put your eye in the beam, but to protect you against the light reflected from what the beam hits.
This is why a laser is more dangerous than a flashlight with the same power.
It is of course possible to use lasers of high frequency but they are harder to manufacture (more spontaneous light emission at high frequencies, you want stimulated emission in a laser) and therefore more expensive.
A infra-red laser does the job better with an invisible beam, which should be hard to detect.
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"Any religion that makes a form of torture into an icon that they worship seems to me a pretty sick sort of religion quite honestly"
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Dr. Mabuse
Septic Fiend
Sweden
9687 Posts |
Posted - 01/04/2005 : 05:02:35 [Permalink]
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quote:
Originally posted by ktesibios
I kind of doubt that a telescope clock drive could be used to track a plane, at least without a lot of modification. The apparent motion of the stars due to the Earth's rotation is only 1/4 degree per minute while an airplane at a low enough altitude to make a laser a threat would be moving a lot faster than that. 
I'm not talking about a simple clock drive. I'm talking about a CCD-camera that is imaging what the telescope can see. A computer analyses the image to see if the fix-star has moved, then calculates where to point the telescope to keep it in focus.
The telescope itself have computerized servo drives for declination and rectascention, and you calibrate the telescope axis by pointing at three different stars to get get the bearing. The computer calculates offsets. Then all you have to do is enter the catalogue number of any of the thousands of objects in the database, and the servos points telescope in the right direction.
Then you can activate the CCD auto-tracking, and the telescope will track the star (or the navigation light of the plane) as it moves.
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Siberia
SFN Addict
Brazil
2322 Posts |
Posted - 01/04/2005 : 05:16:16 [Permalink]
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quote:
Originally posted by Dave W.
quote:
Originally posted by Siberia
But aren't lasers invisible, unless they're in a foggy background? Or are we speaking about different things? Or am I just mis/uninformed? [confused]
If you're looking right at them, they're plenty visible. If you're off to one side of the beam, you'll see less of its light, but not none of it because the beam spreads out just bouncing off air molecules (and more because of dust or moisture or other little tiny stuff).quote:
Either case, I don't doubt they can cause potential damage in long ranges... what I doubt it's that someone could actually pinpoint a person's eye inside a plane's cockpit, and even so, that it would crash a commercial plane. I understand what HH means, but my mind's not connecting it with lasers, only a very strong light [blink]
A powerful enough beam can be extremely bright even at long distances, meaning "pinpoint" accuracy isn't required. But for that high power, we'd be talking military and/or university lasers, and not something at all portable.
Gotcha. It's because I remember an experiment in school that we were demonstrating with lasers and mirrors, and we had to pour baby powder all over the place so other people would actually see it. But I see that one strong enough would be that bright. |
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R.Wreck
SFN Regular
USA
1191 Posts |
Posted - 01/04/2005 : 16:27:37 [Permalink]
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| Man arrested for pointing lasers at aircraft. |
The foundation of morality is to . . . give up pretending to believe that for which there is no evidence, and repeating unintelligible propositions about things beyond the possibliities of knowledge.
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The Cattle Prod of Enlightened Compassion
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Ricky
SFN Die Hard
USA
4907 Posts |
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woolytoad
Skeptic Friend
313 Posts |
Posted - 01/05/2005 : 04:39:09 [Permalink]
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Having done laser experiments very recently ...
quote:
Originally posted by Starman
Lasers with enough power, should not be to hard to get hold of. CO2 lasers (between 9 and 11µm) are available for cutting and drilling and could probably be available with enough power in car portable models.
While CO2 lasers may be small enough to rig up something that will fit in a car, I don't see someone just ordering one. Operation of Class 4 lasers requires the facility to have an interlock system. You cannot be in the room with the laser and turn it on at the same time. If I remember my laser saftey rules correctly ...
quote:
When you play(well work) with a laser you wear protective goggles all the time. Not because you might accidentally put your eye in the beam, but to protect you against the light reflected from what the beam hits.
This is why a laser is more dangerous than a flashlight with the same power.
This is not very clear. A laser is more dangerous than the flash light because the intensity is much much higher. That is, all the power is focused in a thin beam.
quote:
If the laser beam is aimed into the cockpit, light will scatter when the beam hits something (windshield, instruments etc.).
This light will be collected by the eye and as it is monochrome, it has much power in a small frequency band, and the energy will be focused (by the eye) in small points on the retina and in the vitreous chamber where serious and most likely permanent damage will be done.
Monochomicity does not make light more dangerous. You can stare at a sodium lamp quite safely. Sodium lamps mostly emit yellow light of 2 wavelengths. In fact some of the most powerful lasers are hardly monochromatic. I've seen a 5W (this is very very powerful for a laser) Ti sapphire laser. Typical emission of such a laser would peak at 800nm with a spread of 400nm (emission from 600nm to 1000nm).
quote:
You don't have to focus your beam much(which can only be done to a limit as the beam will react with the air molecules) or hit the victims eyes to have an effect.
Depends on the laser. A simple green laser pointer would at most be Class 3A. Such lasers are only harmful if the light is focused and even then the blink reflex will save your eyes. Class 1s are quite safe. Of course pointing any laser in your eye is just bad practice Class 1 or not. You'd probably need a pretty powerful laser not to focus it at all.
BTW: Green is quite easy to make, all you need is a diode laser emitting in the red and an anisotropic crystal (a frequency multiplier if you will). $100.
This is all hysteria in my oppinion. The if its just some bozzo pointing laser pointers in the air then there is no chance of blinding the pilot in both eyes. If this is some weapon, let them spend all their money trying to get it to work. There are easier ways to blind people temporarily.
I wonder what happens if this is a real weapon: Enemy aircraft flying into your territory. You blind him. Aircraft is STILL flying into your territory, but with no pilot. Aircraft crashes into your stockpile of explosives.
Edit: Pointers go up to Class 3A. Classes are 1, 2, 3a, 3b and 4. |
| Edited by - woolytoad on 01/05/2005 18:57:53 |
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Ricky
SFN Die Hard
USA
4907 Posts |
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Dr. Mabuse
Septic Fiend
Sweden
9687 Posts |
Posted - 01/05/2005 : 14:06:59 [Permalink]
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quote:
Originally posted by Ricky
quote:
BTW: Green is quite easy to make, all you need is a diode laser emitting in the red and an anisotropic crystal (a frequency multiplier if you will). $100.
You call that easy? I just want to see your definition of hard...
You know, simple dilithium just won't cut it... |
Dr. Mabuse - "When the going gets tough, the tough get Duct-tape..."
Dr. Mabuse whisper.mp3
"Equivocation is not just a job, for a creationist it's a way of life..." Dr. Mabuse
Support American Troops in Iraq:
Send them unarmed civilians for target practice..
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Ricky
SFN Die Hard
USA
4907 Posts |
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woolytoad
Skeptic Friend
313 Posts |
Posted - 01/05/2005 : 21:59:54 [Permalink]
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quote:
Originally posted by Ricky
quote:
Such lasers are only harmful if the light is focused and even then the blink reflex will save your eyes.
What do you mean by "harmful"? As in cause physical damage to the eye? Because that is not required for a laser to cause a plane to crash, especially when landing. All that needs to be done is to divert the pilots attention away from landing for a few seconds.
Yeah, I was thinking physical damage as that was what I worried about most in the lab. |
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Ricky
SFN Die Hard
USA
4907 Posts |
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woolytoad
Skeptic Friend
313 Posts |
Posted - 01/05/2005 : 23:58:55 [Permalink]
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| Rereading my first post, the majority of it wasn't really trying to give reasons why lasers are bad for blinding pilots. Only that some of Starman's comments are wrong or vague. Only the last two paragraphs contained my oppinions on why people shouldn't worry about people painting planes with lasers. |
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