One major question I have..
... unless I have totally misunderstood how lasers work (quite probable), how does the beam widen to six feet after a certain distance? I thought that the whole point of lasers and the the thing that made them unique was the fact that it was a coherent beam of light and basically that means a dead straight beam of light that does not fan out or decohere. How else do they measure the distance to the moon if the beam is six feet wide by 30,000ft or so, and how spread out would it be a quarter of a million miles later? Obviously they are talking about a beam from a pointer that would realistically at the most be a few hundred mW in power, and I would imagine that a super powerful laser would suffer less decoherence or fanning out.
Boy that , must be one powerful laser! Then again there is the pulsed laser versus continuous beam laser to consider as well. Even things like lasers are not straightforward, in fact they are damned complicated. I'll have to look up exactly how they do dat later.
Actually after looking up spatial and temporal coherence, I see that I am indeed wrong and things are not so simple.
The most monochromatic sources are usually lasers; such high monochromaticity implies long coherence lengths (up to hundreds of meters). For example, a stabilized helium-neon laser can produce light with coherence lengths in excess of 5 m
I suppose the coherence of the ray produced would be directly proportional to the power used to generate it.
Less power - less coherence. More power - more coherence (up to the point of hitting the moon and bouncing back - a half a million mile round trip - to get measurements of the accuracy that can tell us that the moon is is moving away from us a few inches or feet every year (can't remember which it is)). And if you are going to hit a tank from an aeroplane mounted laser weapon, I would imagine that beam or pulse of light would not fan out over equivalent distances. Air to ground as opposed to ground to air. The power would need to be directed at the target and not dispersed over a wide area. A close direct hit of a low power laser beam to the eye will cause blindness, a long range hit would obviously be dispersed quite a bit from the same said powered beam. I also question whether this could even cause the 'just like a photo-flash going off' theory. Mmmm. Not convinced either way. It wouldn't cause blindness and it wouldn't have the power to light the cockpit up either.
But that is just with a pointer type device of low mWs. If you had a 1000mW to play with and the plane was only yards away - I have been there - I had an air side pass when I worked at Heathrow - then yes you could quite easily blind a pilot. The question is, is he using autoland software or doing it old-school? If it is the latter and he doesn't expect to be zapped, then you have just scored a major point. And killed a few hundred people in the process. I've seen pointer devices that go up to 1500mW . Also, is he landing or taking off?
Lasers have always fascinated me, I even did a course when I was at uni to become certified as a laser safety officer. As you can imagine I was taught all about lasers and how they worked, the different designs etc. and obviously most important of all - how not to blind thousands of people at a rave when their pupils are like saucers from the ecstasy and acid - pupil dilation and response has a major effect on the harm that a laser can do - not only are the pupils more dilated hence causing more damage, but the response time is reduced to the fact that the autonomic nervous system does nor respond as it normally would. The blink, or even looking away reflex can save eyesight in the majority of cases where a direct hit has been scored. As stated, this is reduced by the effects of certain pharmaceuticals on the body's natural responses.
Learned the software to generate messages and text and pictures/patterns - pangolin I think it was called - pretty nifty - you could program in a big smiley face to be projected along with the text (i.e. - you are all a load of soap-dodging drug-taking cnuts ;-)).
At one point, after pissing about with pen lasers and learning basic safety - red lasers tend to be less harmful than green lasers, which are less harmful than blue lasers. But it is the wattage of the power source not the colour that is the main factor in when it comes to safety. An 800mW red laser can blind you better than a five mW blue laser.
This guy even brought in the BEAST. A BFO machine that generated some serious wattage. We put our goggles on and marveled at the spectacle. Guy even did the lasers for Jean Michele Jarre at his live events. But I am rambling and reminiscing now. Btw, I never got my safety officer licence - I dropped out, but it was fun...
Out of curiosity and a bit of nostalgia, I wondered what it would cost to actually buy a bona fide laser these days. I do not and have never owned one (apart from inside cd players of course ;-)). But they were a lot more expensive then, now you can get a 5mW one from the net for less than a fiver including delivery. Red ones are cheapest because they are the simplest to make, being able to construct them from a single diode I believe. Green ones are more complicated and hence more expensive, they also tend to be more powerful and dangerous. Blue, more of the same again for the same reasons.
In fact I saw lasers for sale that hit the 1000mW mark. WTF? One direct hit to your retina or a bounce of a mirror/shiny surface will leave you with permanent eye damage. Actually no, not eye damage, that can be achieved by 5mW. Blindness! Apparently it is illegal to buy anything with more than a mW of power in the UK, so even the 5mW ones are technically illegal, although there is no law against importing them - so in theory you could buy one from the states - 1500mW (quite common and not expensive) and have it legally imported. You just can't buy one here. Except that I saw a place advertising 200mW lasers to be bought UK side. Either I don't know what I am talking about (possible), or the law is an ass (likely), or there is some kind of loophole thing going on...
A 200mW laser will blind someone easily. Not sure how good it is for measuring the distance to the moon though.
Sorry for the ramble. Sometimes I'm just not very coherent.
Spatially, temporaly, or linguistically.
Or even logically.
Any physicists out there? Please put me over your metaphorical knee and spank some not so metaphorical sense into me. I love to be educated. I have always loved the subject of light. And don't get me started on the double-slit experiment! Did anyone think of trying that with pulse beamed lasers?