Green Laser pointers: Can you see it >500M away?

[Dark Matter]

If one was using a 30Mw laser for instance under dark skies and moonlit nights, would anyone see that beam if they were more than 500M away or more?

Secondly, we hear that these lasers can reach X distance into the night skies.

When I'm under or near one, I see the beam as a straight narrow beam, but would at say, >1km altitude, would a pilot see that straight beam?

J

[Guest]

30Mw?  Jeezus isnt that illegal? 1mW is the UK limit for people in the street.  PLus Green lazers really screw up pilots. Dont point them at aircraft!!!

[Dark Matter]

I'm licensed to use a green laser >1Mw, as I run an astro tourism business and NO we do not point them at aircraft.. !!!!.

That is why I asked the question; Would anyone see the beam as we do at high altitude and at what land distance from the user, would you NOT see the beam ?

[Photosbykev]

mW = milliWatts : Mw = MegaWatts. There is 10^9 difference in power densities, one could temporarily dazzle/blind a pilot the other would put a hole through the aircraft.

[Dark Matter]

Yep,  I use a 30 megawatt laser this to blow holes in clouds and melt satellites .....LOL....  Ok, ok.. I stand corrected.. it's a 30mW laser.

[laser_jock99]

mW = milliWatts : Mw = MegaWatts. There is 10^9 difference in power densities, one could temporarily dazzle/blind a pilot the other would put a hole through the aircraft.

Beat me to it!

Now a 30Mw hand held laser would awesome....... 

EDIT- going back to OP's question, at 1km the divergence of typical laser pointers means the beam will be about 1m diameter......

[glowjet]

You can see the beam if you are directly behind it, and where it is pointing. Visibility from the side can taper off quite rapidly with low power units and depends on what I believe is called Rayleigh Scattering. You could run an experiment and check your 30mW to see the range it is visible from. There is some pointing data for units of 5mW which have a flash blindness hazard up to 260 feet, Glare disruption from 260 feet to 1,200 feet and a distraction hazard around 1.200 feet up to 11,700 feet, at this height, a fraction over 2 miles, nothing more can be seen. If the wattage of the unit is increased to say 125mW then the distraction hazard extends to something in the order of 11 miles. It is more than understandable that health& Safety have put a recommended power limit of 1mW ( class 2 ) for the general use of lasers in this country, this may be extended to 5mW with trained personnel. Medical information would suggest that no damage is caused to eyesight within these limits, but to extend beyond this range there is a positive danger to eyesight HTH 

[ollypenrice]

I've no idea how to calculate the visibility of a laser beam of x power at different distances but, like Jim, I run an astro tourism business and a few years ago was a bit dismayed to see a prodigious laser rising from some distance away in the south. Ironically this threat to my livelihood came from the Observatoire de Haute Provence! http://www.google.fr/imgres?imgurl=http%3A%2F%2Fobjets.echange.free.fr%2Ffiles%2Fohp%2Flaser.jpg&imgrefurl=http%3A%2F%2Fobjets.echange.free.fr%2F%3Fbrowse%3Dobjet(s)%2520d%27%25C3%25A9change%2520en%2520r%25C3%25A9sidence%2520%25C3%25A0%2520l%27observatoire%2520de%2520Haute%2520Provence&h=594&w=1056&tbnid=7VIMi0uu1v99iM%3A&zoom=1&docid=-60GDeINcc9vYM&ei=oI3OU5eLBMeY1AXp34CACg&tbm=isch&iact=rc&uact=3&dur=3429&page=1&start=0&ndsp=28&ved=0CCIQrQMwAA

It only made about three appearances and has since vanished entirely, which is a bit of a relief. The Observatory is a good hou's drive to our south.

Olly

[acey]

We see light when rays go into our eye and strike the retina. We can see light from a source directly (looking at the sun, light bulb, laser pointer - bad idea) or else we can see reflected light originating from the source (e.g. a wall illuminated by sun or light bulb). The line we see from a laser pointer is light reflected ("scattered") off particles (dust) or molecules (vapour) in the air. If a laser shines through a vacuum then no line will be visible. Scattering weakens the beam, sending some of the light off into different directions, hence limits the effective range.

How far away one would be able to see this scattered light would depend on atmospheric conditions, the precise details of the laser, the acuity and adaptation of the viewer, and their distance from the beam.

Visibility of light directly from a laser, or reflected back from a target, is a far simpler problem, best tested by actual experiment. This website reports direct visibility of a 1mW beam at a range of 20km. If you had a sufficiently powerful telescope then you would presumably be able to see a 1mW laser from the Moon, or indeed from any distance.

http://kotaku.com/one-mans-quest-to-prove-how-far-laser-pointers-reach-1464275649

The following website has interesting information about laser hazard, particularly in relation to aircraft. It says that the main hazard is distraction rather than visual damage. For a 1W laser the eye injury hazard distance is 733 feet.

http://www.laserpointersafety.com/page52/laser-hazard_diagram/different-lasers-compared.html

This is also worth a look:

http://www.repairfaq.org/sam/lasersaf.htm#safavia

[Dark Matter]

I've no idea how to calculate the visibility of a laser beam of x power at different distances but, like Jim, I run an astro tourism business and a few years ago was a bit dismayed to see a prodigious laser rising from some distance away in the south. Ironically this threat to my livelihood came from the Observatoire de Haute Provence! http://www.google.fr/imgres?imgurl=http%3A%2F%2Fobjets.echange.free.fr%2Ffiles%2Fohp%2Flaser.jpg&imgrefurl=http%3A%2F%2Fobjets.echange.free.fr%2F%3Fbrowse%3Dobjet(s)%2520d%27%25C3%25A9change%2520en%2520r%25C3%25A9sidence%2520%25C3%25A0%2520l%27observatoire%2520de%2520Haute%2520Provence&h=594&w=1056&tbnid=7VIMi0uu1v99iM%3A&zoom=1&docid=-60GDeINcc9vYM&ei=oI3OU5eLBMeY1AXp34CACg&tbm=isch&iact=rc&uact=3&dur=3429&page=1&start=0&ndsp=28&ved=0CCIQrQMwAA

It only made about three appearances and has since vanished entirely, which is a bit of a relief. The Observatory is a good hou's drive to our south.

Olly

Maybe it was using one of the lasers to guide on a star? similar to what they use at the ESO facilities in the Andes.

What laser do you use, Olly?

Since I posted my first thread,have since been given permission from our Aviation authorities, the local Council and Police,to use my 30mW laser during our night shows, when we move the facility (see www.maidenwellobservatory.com) to some land adjacent to the rural airstrip at Kingaroy. We hope to be up and running by March 1 2015,  if not earlier.

[happy-kat]

Just a question but why do you need to have a 30 rated one?

Would a device power in a lower range not suffice?

[ollypenrice]

Maybe it was using one of the lasers to guide on a star? similar to what they use at the ESO facilities in the Andes.

What laser do you use, Olly?

Since I posted my first thread,have since been given permission from our Aviation authorities, the local Council and Police,to use my 30mW laser during our night shows, when we move the facility (see www.maidenwellobservatory.com) to some land adjacent to the rural airstrip at Kingaroy. We hope to be up and running by March 1 2015,  if not earlier.

No, it wasn't an adaptive optics device, thank heavens, or it would have been on forever. It is some sort of cloud researching device.

I just use a galaxy products laser, very reliable, with good battery life. I can no longer find them on the net. These things http://www.google.fr/imgres?imgurl=http%3A%2F%2Fwww.astronomylasers.com%2Fimages%2Fimg1.jpg&imgrefurl=http%3A%2F%2Fwww.astronomylasers.com%2F&h=533&w=800&tbnid=tyGGRZusv-wUJM%3A&zoom=1&docid=rSUjXd-s_lGuhM&ei=EFzRU6SVH8rD0QWu84DYCQ&tbm=isch&iact=rc&uact=3&dur=577&page=1&start=0&ndsp=27&ved=0CEwQrQMwDg  come up everywhere and are bright but tacky and pack up easily. They also eat batteries. I have a couple but use my old Galaxy Products one most of the time and dread the day when it pegs out. I've had it 7 years. It has a nice stainless steel body. If anyone knows where you can find them I'd love to know.

Olly

[Dark Matter]

Just a question but why do you need to have a 30 rated one?

Would a device power in a lower range not suffice?

I use a 30mW for all nights - moonless and moon.

In bright moonlight being out in the bush, less powerful laser beams are 'drowned out' in the strong moonlight and when you have 40 standing around you, unless you are under or very close to the beam, you can't really see it.

I've tried 5, 20 and 30 mW lasers and only the last one does the job.