As you are probably aware, in SI units, Power (in watts) is defined as energy (in Joules) over time (seconds). Similarly, watt per square meter or a joule per second per square meter is power per unit area (m2).
A beam of photons at 1250 watts per square meter will carry the same amount of power per unit area and hence energy per unit time and area irrespective of the wavelength, spatial or chromatic coherence....
Am I still coherent or has the red wine and late night got to me?
Well said Susan...as coherent as a He-Ne laser!
I see what you are saying with regard to power per unit area.....but I suspect there is also the rub...assuming a 100mw beam diverges to say 200mm after a kilometer or so (this approximates my pointer's performance) then the flux in our 1mm beam is being spread over pi*r**2 in area or about 31,000x the area....hence if a
person with say a 6mm pupil is "flashed" we'd have about 5000x less energy going into their eye than say over a few metres...about 0.02 of a milliwatt?
I hate that governments will go as far as to ban low output lasers.
Low output lasers have divergence that will cover an entire airplane in a green dot as powerful as your normal lightbulb at that distance. Surely not enough to blind a pilot even temporarily.
You can banter all you like with respect to retinal damage, joules and mw's but lets face it, has anyone actually tested it?
Well here goes, I have a 10Mw 532nm Green laser and I live opposite a large hill that has a lookout on it, according to my GPS this lookout is 3000 mtrs from my rear deck and certainly has line of site to it. No houses, roads or airports are near this lookout, green tree frogs can just close their eyes.
As I am convinced that my eyesight will not be harmed by this experiment, I am going to perform a test this weekend, I certainly would not look in to the laser under 10 mtrs, in fact under 50 mtrs, however, I would certainly risk looking at it from 3000 mtrs. I will drive to the lookout with a torch, shine the torch at my house and (via mobile phone) have my wife fire the laser at me (at the torch), I suspect I will see a vaguely annoying green halo around a moderately bright but not blinding green dot.
I will publish my findings here in the next few days.
I for one will not bother with licensing or any such ban, I am a responsible user and the authorities can go jump, our lives are already way to controlled by these morons. An old bumper sticker said "If you outlaw guns only outlaws will have guns", they outlawed guns and guess what? People are still being shot. Prohibition has NEVER worked and never will. It is impossible to police and therefore a storm in a teacup IMHO. These are valuable tools, I use mine on my ETX90 to guide my 12" DOB, I highly recommend this method of guiding as a cheap alternative to expensive pushto systems if you already own a goto scope or cube. It has the added benefit of naked eye pointing as well, good when trying to find exactly what your viewing.
Yet another report on the news last night where the Premier said that they have the capability to bring down a plane and that he want's a complete ban on all lasers. Astronomers and other professionals would be exempt.
Two thoughts come to mind.
1. If a laser is so effective, why do terrorists need to spend tens of thousands of dollars on ground to air missiles if all you need is a laser worth $100.
2. As amateur astronomers are not mentioned in the exemptions does anyone know where I can buy an online degree that says I am a professional astronomer.
When you shine a laser through a telescope, you get a collimated beam that goes MUCH further without diverging.
Take a look here. I shone my green laser through a 6 inch telescope and painted a design on a green water tank some kms away. Of course I knew what I was doing and made sure it only staye don the tank and not near any of the houses. The big concern is if idiots realise this abnd start shining more powerful home made lasers using 250 milliwatt laser diodes found in cheap DVD burners, through telescopes, they could impact airliners flying at 30 000 feet.
So what happens if someone uses a telescope and laser in such a manner against high flying aircraft, will they seek to ban telescopes too? I will be a double criminal then as I will not be handing in either my laser or telescopes even if they are declared illegal.
A .303 rifle has a range of up to 5 kms, so anything with long range has the potential to be mis used. What the govt must do is have tough penalties for the mis-users, not for everyone else possessing the equipment.
i only have a 5mw green laser, it was my second after one of those tiny red ones. I was interested in getting a extremyl powerful one. My 5mw cant shine a beam in the sky and pointing at stars. it can though go over 1km, 2 maybe.
So... where can i get a cheap ($0-$80) and powerful (50-200), also a nice colour(which includes green but excludes red. (maybe)).
i only have a 5mw green laser, it was my second after one of those tiny red ones. I was interested in getting a extremyl powerful one. My 5mw cant shine a beam in the sky and pointing at stars. it can though go over 1km, 2 maybe.
So... where can i get a cheap ($0-$80) and powerful (50-200), also a nice colour(which includes green but excludes red. (maybe)).
Cheap and powerful for $0-$80 - ebay
Not as cheap, powerful and dependable - dedicated laser pointer sellers such as http://www.laserpointerking.com/main.asp,mode,1,,.htm
Even less cheap, but local - MyAstro, Bintel
I see what you are saying with regard to power per unit area.....but I suspect there is also the rub...assuming a 100mw beam diverges to say 200mm after a kilometer or so (this approximates my pointer's performance) then the flux in our 1mm beam is being spread over pi*r**2 in area or about 31,000x the area....hence if a
person with say a 6mm pupil is "flashed" we'd have about 5000x less energy going into their eye than say over a few metres...about 0.02 of a milliwatt?
Hi Peter, and also Nightshift,
a few more rough calculations...
of course the power density (energy per square meter) will fall off hugely as the beam diverges. By the time it has spread out to 200 mm diameter from 1 mm diameter, the energy per unit area will have fallen by a factor of (100X100)/(0.5x0.5) = 40,000, so the 1 mW 1 mm beam will have fallen from an effective 1250 w/m2 to the equivalent of about 40 W/m2.
While will not enough to cause eyesight damage, it will still be very bright - remember that for a laser, the rated power is the radiant output power - not the electrical input power.
A 100 watt incandescent lightbulb is only about 3% efficient, so there is really only about 3 watts of light coming out, the rest is waste heat. So a laser with a diverged 200 mm beam will appear about as bright as a 1300 watt lightbulb at 1 metre...
If you are flying at 10 metres of the ground at 250 knots in a crosswind and in the dark and someone flashes a 1.3 kW lightbulb in your face, you may lose a little bit of concentration as well as some night vision...
Dennis I applaud your decision to go "hands on" with this, the scientist in me is bubbling with enthusiasm at this experiment. I'm keen to see what your opinion is after performing this test.
I got a very nice snail mail reply from Kay Hull to my email the next day. Assuring me that she agrees with our concerns re the legitimate use of lasers. No reply from the two ministers as yet.
Getting action out of canberra would not be too much different than dealing with a local council, all that would change would be the scale. I would imagine anything over $50k would get the ball rolling. Anything under would no doubt be taken as an insult. Especially by a federal minister.
Of course if your big enough you can offer a lifetime seat on the board of your company. @ around $150k/ annum.
too late, already more or less banned here in vic, its just a knee jerk reaction to a few idiots who will not be brought into line by these regulations.
we live in a society that has fear pushed at it all the time as though
everyone is a terrorist.
Funny thing though as someone who has been a bowhunter for over 30 years i own equipment that would easily kill anything that lives on land in this country, and i could use it and if you were standing 20 meters away you would hear virtually nothing. No licence required and your 10 year old son could buy all gear required no questions asked.
In what no doubt is seen as a futile experiment, recently I shone my 100 milliwatt green laser though the 10 inch scope at the biggest laser reflector Apollo crews left on the Moon, after looking up a map of its location, then, Id quickly take away the laser and look throuhg the scope in the hope of seeing a return 4 secs later. I saw nothing. The NAS's resident mirror maker George estimated that even properly focussed the spot might be several Kms across by the time it reaches the moon, and the reflector is only about a metre oor so across if that, so thats a tiny part of that 100 mw to be reflected back. later on I read that the lasers use to actually do this from Earth are around 4 watts or so, much more powerful than mine.
Still, it was interesting to try. Looking through my 6 inch scope along side, I could clearly see a bright green dot projected on high Currus clouds shining the laser through the 10 inch scope, as a 10 inch wide beam is much less divergent than a 2 mm wide beam.
Scott
Unfortunately it seems shining a bright coherent light at some of my fellow aviators is being perceived as some sort of hazard. I beg to differ.
Perhaps twits who do not dip their car's high-beam at night should be goaled for a couple of years as well.
Next to go will be the display of any "white pointers" particularly at Swanbourne beach (well known the military aviators in Perth!)...a true risk(ay) aviation hazard if there was one!
